chemistry · 2 which one of the following amino acids is optically active and produces a neutral...

TIME

1 hour 15 minutes.

INSTRUCTIONS TO CANDIDATES

Write your Centre Number and Candidate Number in the spaces provided at the top of this page.Answer all sixteen questions.Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering.Answer all six questions in Section B. Write your answers in thespaces provided in this question paper.

INFORMATION FOR CANDIDATES

The total mark for this paper is 90.Quality of written communication will be assessed in question 14(c).In Section A all questions carry equal marks, i.e. two-marks for each question.In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question.A Periodic Table of Elements (including some data) is provided.

ADVANCEDGeneral Certificate of Education

2006

Chemistry

Assessment Unit A2 2assessing

Module 5: Analytical, Transition Metals and Further

Organic Chemistry

[A2C21]

FRIDAY 2 JUNE, MORNING

A2.2: 2006 - 2012006-09: Old Old SpecJune 2010-1 : Old Spec

245 pages in total here.

6

6

www.franklychemistry.co.uk

http://code-industry.net/







Section A

For each of the questions only one of the lettered responses (A – D) is correct.

Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet.

1 Which one of the following is the electronic structure for the titantium ion, Ti2+, in the ground state?

A 1s22s22p63s23p64s2

B 1s22s22p63s23p63d2

C 1s22s22p63s23p63d14s1

D 1s22s22p63s23p43d24s2

2 Which one of the following amino acids is optically active and produces a neutral solution when dissolved in water?

A NH2CH2COOH B NH2CHCOOH | CH3

C NH2CHCOOH | (CH2)4 | NH2

D NH2CHCOOH | CH2 | COOH

3 Which one of the following statements about benzene is incorrect?

A A total of six electrons per molecule are delocalised. B All of the carbon-carbon bonds are the same length. C The bond angles are all 120°. D The empirical formula is C6H6.






4 Which one of the following analytical techniques depends upon electronic transitions between energy levels?

A infra-red spectroscopy B mass spectrometry C n.m.r. spectroscopy D visible spectroscopy

5 1.06 g of hydrated sodium carbonate, Na2CO3.10H2O, were neutralised by 12.5 cm3 of dilute hydrochloric acid. What is the concentration of the acid in g dm–3?

A 10.8 (1:1) B 21.6 (correct) C 29.2 (anhydrous, 1:1) D 58.4 (anhydrous, 1:2)

6 Which one of the following graphs represents the absorbance against volume in a colorimetry experiment for the solutions of copper(II) sulphate and ammonia given?

absorbance

0 5 1010 5 0 0.1M NH3(aq)

0.05M CuSO4(aq) 0 5 1010 5 0 0.1M NH3(aq)

0.05M CuSO4(aq)6.663.33

3.336.66

absorbance

0 5 1010 5 0 0.05M NH3(aq)

0.1M CuSO4(aq)6.663.33

3.336.66

absorbance

0 5 1010 5 0 0.05M NH3(aq)

0.1M CuSO4(aq)

A

absorbance

DC

B






7 In which one of the following complex ions is the metal ion in the oxidation state +2?

A [Cr(H2O)5OH]2+

B [CuCl4]2–

C [Fe(SCN)(H2O)5]2+

D [TiCl6]2–

8 The order of increasing basic strength for ammonia, phenylamine and propylamine is

A ammonia, phenylamine, propylamine B phenylamine, propylamine, ammonia C phenylamine, ammonia, propylamine D propylamine, ammonia, phenylamine

9 Methylamine reacts with excess ethanoyl chloride according to the equation:

CH3COCl + CH3NH2 → CH3NHCOCH3 + HCl

6.00 g of N-methyl ethanamide were produced from 4.24 g of methylamine. What is the percentage yield?

A 60.0% (correct) B 66.0% (use ethanoyl chloride etc) C 70.6% (use mass) D 78.6%

10 26.65 g of [Cr(H2O)5]3+.2Cl–.H2O were dissolved in water. The solution was treated with excess silver nitrate solution. What mass of silver chloride precipitate was formed?

A 7.17 g (2:1 ratio) B 14.35 g (only 1 Cl) C 28.70 g (correct) D 43.05 g (3 Cl)






Section B

Answer all six questions in the spaces provided.

11 Platinum finds extensive use in medicine, for example in cisplatin, and as a catalyst in industry.

(a) (i) Draw the structure of cisplatin.

[2]

(ii) State one use of cisplatin in medicine.

__________________________________________________ [1]

(b) A mixture of ammonia and oxygen is both kinetically and thermodynamically stable. The reaction between ammonia and oxygen is catalysed by platinum.

(i) State the effect of platinum on the thermodynamic and kinetic stability of this mixture.

thermodynamic stability _________________________________

__________________________________________________ [1]

kinetic stability ________________________________________

__________________________________________________ [1]

(ii) The reaction produces nitrogen(II) oxide and steam. Write the equation for this reaction.

__________________________________________________ [2]






12 Toluene (methylbenzene), C6H5CH3, is used to make artificial sweeteners, pharmaceuticals and explosives.

(a) Monobromination of the aromatic ring in toluene results in three possible structural isomers.

(i) Draw two of the structural isomers.

[2]

(ii) Name a suitable catalyst for this reaction.

__________________________________________________ [1]

(iii) Explain why toluene undergoes substitution rather than addition with bromine.

_____________________________________________________

_____________________________________________________

__________________________________________________ [2]

(b) The explosive trinitrotoluene (TNT) is prepared by refluxing toluene with a nitrating mixture containing the NO2

+ ion.

(i) Name the NO2+ ion.

__________________________________________________ [1]

(ii) Name the two reagents used in the nitrating mixture.

_____________________________________________________

__________________________________________________ [2]

(iii) Draw a flow scheme for the mechanism of the mononitration of toluene.

[3]






13 Proteins are synthesised from 20 essential amino acids. Recent research has shown that some organisms also use another amino acid called selenocysteine, which is shown below.

H | NH2 — C — COOH | CH2SeH

(a) (i) Explain why selenocysteine, like other amino acids, has a high melting point.

_____________________________________________________

__________________________________________________ [2]

(ii) State and explain if selenocsyteine is optically active.

_____________________________________________________

__________________________________________________ [2]

(b) Selenocysteine reacts with sodium carbonate solution. Write an equation for the reaction.

______________________________________________________ [2]

(c) Some E. coli bacteria contain selenoproteins which are enzymes.

(i) Draw the structure of the dimer formed between two selenocysteine molecules and circle the peptide link.

[3]






(ii) Explain the mechanism by which an enzyme acts.

_____________________________________________________

_____________________________________________________

__________________________________________________ [2]

(iii) On the axes below sketch how the enzyme activity is affected by altering the pH.

[1]pH

activity






14 Industrial wastewater often contains dissolved metals, such as copper, which must be reduced to low, non-toxic levels before discharge into rivers.

(a) State how you could detect the presence of aqueous copper(II) ions in the untreated wastewater.

_________________________________________________________

______________________________________________________ [2]

(b) Suggest how copper(II) ions may be removed from industrial wastewater.

______________________________________________________ [1]

(c) Describe how you could use a titrimetric technique to determine the concentration of copper(II) ions in the effluent water.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

______________________________________________________ [5]

Quality of written communication [2]






15 The homologous series of alcohols can be ascended using a suitable synthetic route e.g. ethanol is converted to propan-1-ol as follows:

HBr A CH3CH2OH → CH3CH2Br → CH3CH2CN

↓ B

CH3CH2CH2NH2

↓ C

CH3CH2CH2OH

(a) State the name, or formula, of the reagents required for steps A, B and C.

A _______________________________________________________

B _______________________________________________________

C ____________________________________________________ [3]

(b) A mass spectrometer can be used to distinguish between ethanol and propan-1-ol.

(i) Identify the ion which would give rise to a peak at m/e = 17 for both ethanol and propan-1-ol.

__________________________________________________ [1]

(ii) Suggest one ion which may be detected in the mass spectrum of propan-1-ol but not for ethanol.

__________________________________________________ [1]






(c) The first step involves conversion of ethanol to bromoethane. The n.m.r. spectra of these compounds are shown below.

Source: http://www.steve.gb.com/images/science/ethanol_nmr_spectrum.png

Source: http://www.brynmawr.edu/Acads/Chem/mnerzsto/Image16.gif

9 8 7 6 5 4 3 2 1 0δ

ethanol

5.0 4.0 3.0 2.0 1.0 0 ppm

bromoethane

“a”

“b”Br-CH2CH3

“a” “b”






Compare and contrast these two spectra with particular reference to chemical shift, peak integration and spin-spin splitting.

chemical shift

_________________________________________________________

_________________________________________________________

_________________________________________________________

______________________________________________________ [2]

peak integration

_________________________________________________________

_________________________________________________________

_________________________________________________________

______________________________________________________ [2]

spin-spin splitting

_________________________________________________________

_________________________________________________________

_________________________________________________________

______________________________________________________ [2]






[Turn over

16 Colour plays an important part in chemistry whether to perform analytical tests or to manipulate molecular structures to achieve desired shades.

(a) State a chemical test for iron(II) ions in solution.

_________________________________________________________

______________________________________________________ [2]

(b) The colour of a transition metal complex is affected by the ligands attached to the metal ion. This is illustrated by the following equilibrium:

[Cu(H3O)6]2+(aq) + 4Cl–(aq) [CuCl4]2–(aq) + 6H2O(l)

(i) State the colour of the two copper complexes.

[Cu(H3O)6]2+(aq) ______________________________________

[CuCl4]2–(aq) _______________________________________ [2]

(ii) State the shape of the hexaaquacopper(II) ion.

__________________________________________________ [1]

(iii) Name a suitable reagent which could be added to the equilibrium to shift it to the right.

__________________________________________________ [1]

(c) 1,2-diaminoethane is a bidentate ligand which complexes with aqueous nickel(II) ions.

(i) Draw the structure of 1,2-diaminoethane.

[1]









(ii) Suggest what is meant by the term bidentate ligand.

_____________________________________________________

_____________________________________________________

__________________________________________________ [2]

(iii) State the colour and formula of the complex formed when excess 1,2-diaminoethane (represented as ‘en’) is added to aqueous nickel(II) ions.

colour _______________________________________________

formula ___________________________________________ [2]

(d) Chrysoidine was the first commercially useful azo dye. It was produced by the reaction of 1,3,5-triaminobenzene and benzene diazonium chloride.

(i) Draw the structure of Chrysoidine, circling the azo group.

[3]

(ii) Explain why Chrysoidine is coloured.

_____________________________________________________

_____________________________________________________

__________________________________________________ [2]

(iii) Other functional groups may be incorporated onto the benzene ring. Suggest one reason why altering the attached functional group may be useful in the dyestuffs industry.

__________________________________________________ [1]






(e) Benzenediazonium chloride reacts with aqueous sodium sulphite to produce phenylhydrazine.

C6H5N2Cl + 2Na2SO3 + 2H2O → C6H5NHNH2 + 2Na2SO4 + HCl

(i) State the role of sodium sulphite in this reaction.

__________________________________________________ [1]

(ii) In an experiment the yield of phenylhydrazine was 45.36 g. Calculate the volume of 2 M sodium sulphite solution required to produce this amount assuming an 80% yield.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

__________________________________________________ [4]






ADVANCEDGeneral Certifi cate of Education

2006

MARKSCHEME

ChemistryAssessment Unit A2 2

assessing

Module 5: Analytical, Transition Metals and Further Organic Chemistry

[A2C21]

FRIDAY 2 JUNE, MORNING






Section A

1 B

2 B

3 D

4 D

5 B

6 B

7 B

8 C

9 C

10 A

[2] for each correct answer [20] 20

Section A 20






Section B

11 (a) (i) H3N

[2]

(ii) Anti-tumour/anti-cancer [1]

(b) (i) None [1] decreases [1] [2]

(ii) 4NH3 + 5O2 → 4NO + 6H2O [2] 7 unbalanced = [–1]

12 (a) (i)

All three [2] two [1] [2]

(ii) Iron/iron(III) bromide or aluminium/aluminium bromide [1]

(iii) Stability of benzene ring [1] addition – no delocalisation [1] [2]

(b) (i) Nitronium ion/nitryl cation [1]

(ii) Concentrated sulphuric acid [1] concentrated nitric acid [1] [2]

(iii)

each error [–1] Any position of nitro group accepted [3] 11

ClPt

Cl

CH3Br

CH3

Br

CH3

Br

H3N

CH3

+ NO2 →

CH3

NO2

CH3

NO2

→ + H++

H






13 (a) Dipolar ions/zwitterion [1] strong attractions (between opposite charges) [1] [2]

(b)

unbalanced = [–1] [2]

(c) (i)

structure [2] circle [1] [3]

(ii) lock and key mechanism [1] weakens bonds/lowers activation energy/active site [1] Maximum of [2] [2]

(iii) Bell curve [1] 10

14 (a) Add sodium/potassium hydroxide/carbonate ions/ion exchange [1]

(b) Titrate against standard [1] edta4– [1] indicator – murexide [1] (buffered to) pH of 8/ammonia + ammonium chloride [1] colour change from green/yellow [1] to purple/mauve/blue/violet [1] Maximum of [5] [5]

Quality of written communication [2] 8

15 (a) A = NaCN/KCN [1] B = LiAlH4/Na and C2H5OH [1] C = HNO2/NaNO2 and HCl [1] [3]

(b) Extra peak due to OH [1] at high chemical shift [1] two (superimposed) spectra [1] 2 quartets [1] 2 triplets [1] to maximum of [2] [2]

2NH2 — C — COOH + Na2CO3 → 2NH2 — C — COONa + H2O + CO2

——

CH3

CH2SeH

—

CH2SeH

— CH3

NH2 — C — C — N — C — COOH

——

H

CH2SeH

—

CH2SeH

H— — —O H —








(c) (i) OH+ [1]

(ii) CH3CH2CH2+/CH3CH2CH2OH+ etc. [1]

(d) (i) Time/retention time [1]

(ii) (Comparison of) area under each curve [1]

(e) 12 g propan-l-ol = 0.2 mole reacts with 0.2 × 4.5 mole oxygen = 0.9 mole volume of oxygen = 0.9 × 24 = 21.6 dm3

volume of oxygen in 120 dm3 of air = 0.2 × 120 = 24 dm3

excess oxygen = 24 – 21.6 = 2.4 dm3

volume of nitrogen etc. left = 120 –24 = 96 dm3 [1] volume of carbon dioxide formed = 0.2 × 3 = 0.6 mole = 14.4 dm3 [1] total volume of gas = 2.4 + 96 + 14.4 = 112.8 dm3 [1] award [4] directly for correct answer each error [–1] [4] 13

16 (a) Add (aqueous) sodium hydroxide [1] green ppt [1] [2]

(b) (i) Blue [1] Green/yellow [1] [2]

(ii) Octahedral [1]

(iii) Hydrochloric acid/sodium chloride/any soluble chloride [1]

(c) (i) or NH2(CH2)2NH2 [1]

(ii) Two [1] co-ordinate bonds/points of attachment/lone pairs donated [1] [2]

(iii) violet/purple/mauve [Ni(en)3]

2+ [1] [2]

(d) (i)

structure [2] Each error [–1] azo group [1] [3]

N — CH2 — CH2 — N—H

H ——

H

H—

N

NOH









15A2C2S6P

(ii) Conjugated/delocalised electrons/chromophore [1] absorbs visible radiation [1] to promote electrons (to higher energy level) [1] Any two [2]

(e) (i) Oxidation number of sulphur goes from +4 to +6 ∴ reducing agent [1]

(ii) RMM phenylhydrazine = 108 moles = 45.36/108 = 0.42 moles sodium sulphite = 2 × 0.42 = 0.84 volume = 0.84 × 1000/2 = 420 cm3

80% = 420/0.8 = 525 cm3

each error [–1], carry error through [4] 21

Section B 70

Total 90









TIME

1 hour 30 minutes.


Write your Centre Number and Candidate Number in the spaces

provided at the top of this page.

Answer all fifteen questions.

Answer all ten questions in Section A. Record your answers by

marking the appropriate letter on the answer sheet provided. Use only

the spaces numbered 1 to 10. Keep in sequence when answering.

Answer all five questions in Section B. Write your answers in the

spaces provided in this question paper.


The total mark for this paper is 90.

Quality of written communication will be assessed in

question 13(a)(v).In Section A all questions carry equal marks, i.e. two marks for each

question.

In Section B the figures in brackets printed down the right-hand side

of pages indicate the marks awarded to each question or part question.

A Periodic Table of Elements (including some data) is provided.


2007

Chemistry

Assessment Unit A2 2

assessing


Organic Chemistry

[A2C21]

WEDNESDAY 30 MAY, AFTERNOON









[Turn over

Section A



1 Which one of the following formulae represents the complex formed when excess ammonia

solution is added to cobalt(II) sulphate solution?

A [Co(NH3)4(H

2O)

2]2+

B [Co(NH3)4]2+

C [Co(NH3)6]2+

D [Co(NH3)2(H

2O)

4]2+

2 Which one of the following organic compounds gives rise to the largest number of peaks in a

high resolution n.m.r. spectrum?

A CH3CH

2COCH

2CH

3

B CH3COOH

C CH3CH

2Br

D CH3CH

2COOCH

3

3 In which one of the following complexes does the transition metal present have an oxidation

state of +2?

A [Co(NH3)4Cl

2]Cl

B [Cu(CN)4]3–

C K3[Fe(CN)

6]

D [Ni(en)3]Cl

2

4 What is the total number of isomers of dichlorobenzene, C6H

4Cl

2?

A 2

B 3

C 4

D 5









5 The magnesium content of a sample of water may be determined by titration with edta using

a suitable indicator. Which one of the following statements is incorrect?

A One mole of edta reacts with one mole of magnesium ions.

B The solution must be buffered at a pH of approximately 10.

C The complex formed between edta and magnesium ions is coloured.

D The magnesium ions forms a stable complex with the indicator.

6 Sulphur dichloride dioxide, SO2Cl

2, reacts with water to form a mixture of only hydrochloric

acid and sulphuric acid. Calculate the hydrogen ion concentration of the solution formed

when 0.02 mole of SO2Cl

2 is dissolved to make 250 cm3 of solution.

A 0.08 mol dm–3

B 0.16 mol dm–3

C 0.24 mol dm–3

D 0.32 mol dm–3

7 In the reaction

which species attacks the benzene ring?

A HNO3

B NO2

C NO2

+

D H2NO

3+

NO2O2N

NO2

CH3

HNO3/H2SO4⎯⎯⎯⎯→

CH3






8 A mixture of two amino acids was subjected to “two-way” chromatography. After elution

with solvent 1 the paper was removed, dried and rotated through 90° and eluted with

solvent 2. The resultant chromatogram is shown below.

The Rf values for some amino acids are given.

amino acid Rf (solvent 1) Rf (solvent 2)

alanine 0.30 0.65

aspartic acid 0.14 0.37

glycine 0.29 0.42

lysine 0.21 0.52

valine 0.54 0.65

Which two amino acids does the mixture contain?

A alanine and aspartic acid

B alanine and valine

C glycine and lysine

D glycine and valine

solvent front 1

solv

ent fro

nt 2

originalspot






9 50 cm3 of a gaseous hydrocarbon requires exactly 250 cm3 of oxygen for complete

combustion and produces 150 cm3 of carbon dioxide. What is the formula of the

hydrocarbon?

A C3H

4

B C3H

8

C C5H

10

D C5H

12

10 Each of the copper compounds below can be reduced to the metal. Which one of the

compounds would produce the greatest mass of copper metal if 5.0 g of each compound were

reduced?

A CuO

B Cu2O

C CuS

D CuF2






Section B

Answer all five questions in the spaces provided.

11 Instrumental analysis is commonly used to deduce the identity and structure

of unknown organic compounds. An organic compound of molecular

formula C5H

10O was subjected to a series of tests.

(a) The compound produced the following mass spectrum:

Suggest the formulae of two ions which would give rise to the peak at

m/e 43.

__________________________________________________________

_______________________________________________________ [2]

43100

%abundance

m/e






(b) The infra-red spectrum for the compound is shown below:

Identify the functional group which has the largest absorbance.

_______________________________________________________ [1]

(c) Use your answers to parts (a) and (b) to deduce the structural formula

of the compound.

_______________________________________________________ [1]

4000 3000 2000 1500 1000

0

100

Absorbance

C

Bond Absorption Bond Wavenumber/cm–1

C––H 2850–3300

C––O 1000–1300

O––H 2500–3500

C––O 1680–1750






12 Para red is a dye which was detected in cayenne pepper sourced from

Uzbekistan. The discovery of this banned dye in foodstuffs led to

withdrawal of many products from supermarket shelves. The dye can be

prepared as follows:

(a) (i) Name the reagents used in step A.

______________________________________________________

____________________________________________________ [2]

(ii) Explain why a low temperature must be used in step A.

______________________________________________________

____________________________________________________ [1]

(b) (i) Deduce a possible structure for Para red.

[2]

(ii) Explain why Para red is coloured.

______________________________________________________

____________________________________________________ [2]

NO2

N2 Cl–

A⎯→

NH2

NO2

⎯⎯⎯⎯→

OH

Para red

+






13 Transition metal chemistry is characterised by redox reactions, colour

changes and catalytic activity.

(a) The most common oxidation states in iron compounds are +2 and +3.

Iron(II) ions are readily oxidised to iron(III).

(i) Define the term oxidation in terms of electron transfer.

____________________________________________________ [1]

(ii) Iron(II) ions may be oxidised by bubbling chlorine gas through an

aqueous solution of the ions. State the colour change observed and

write an equation for the reaction.

______________________________________________________

____________________________________________________ [3]

(iii) State the electron structure of an iron(II) ion and an iron(III) ion

using spd notation.

iron(II) __________________________

iron(III) __________________________ [2]

(iv) Use the above electron structures to explain the relative stabilities

of the two ions.

______________________________________________________

____________________________________________________ [1]






(v) Describe how the percentage of iron in aluminium foil may be

determined using colorimetry. Your account should include how

you would:

● dissolve the foil

● oxidise the iron to the +3 oxidation state

● use a named reagent to produce a strongly coloured complex

● use a calibration curve to determine the concentration of iron in

solution

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

____________________________________________________ [4]






(b) Trinitrotriammine cobalt(III), [Co(NO2)3(NH

3)3], is a yellow crystalline

substance which may be prepared by the following method.

Dissolve 12.2 g of cobalt(II) ethanoate tetrahydrate in 100 cm3 of hot water. Cool the solution in an ice-bath and add 10.4 g of sodium nitrite dissolved in 50 cm3 of “0.88” ammonia. Cool to 10 °C and carefully add 14 cm3 of 20 volume hydrogen peroxide solution followed by 2 g of activated charcoal. After stirring, the mixture is left for 10 minutes before boiling for 30 minutes. Filter the hot solution to remove the activated charcoal and cool the filtrate in an ice-bath. Filter off the crystals, wash with cold ethanol and dry.

(i) Deduce the formula of cobalt(II) ethanoate tetrahydrate.

____________________________________________________ [2]

(ii) State and explain the role of hydrogen peroxide in this preparation.

______________________________________________________

____________________________________________________ [2]

(iii) Suggest the shape of the trinitrotriammine cobalt(III) complex.

____________________________________________________ [1]

(iv) Deduce the coordination number of cobalt in the trinitrotriammine

cobalt(III) complex.

____________________________________________________ [1]

(v) 20 volume hydrogen peroxide is so named because one volume of

the solution produces 20 times this volume of gaseous oxygen on

complete decomposition at 20 °C and one atmosphere pressure i.e.

1 cm3 of solution will produce 20 cm3 of oxygen gas.

2H2O

2(aq) → 2H

2O(l) + O

2(g)

Calculate the concentration of 20 volume hydrogen peroxide in

mol dm–3.

______________________________________________________

______________________________________________________

____________________________________________________ [3]





(c) Aqueous cobalt(II) ions catalyse the decomposition of chlorate(I) ions,

ClO–, to form oxygen gas.

(i) Use three equations to show the three steps involved in this

catalytic decomposition.

______________________________________________________

______________________________________________________

____________________________________________________ [3]

(ii) Explain whether this catalysis is homogeneous or heterogeneous.

______________________________________________________

____________________________________________________ [1]





[Turn over

14 Cyanides are salts of hydrocyanic acid (hydrogen cyanide). Organic

cyanides have the formula RCN and are called nitriles.

(a) Potassium cyanide is used to extract gold from its ore according to the

following reaction:

4Au(s) + 8CN–(aq) + 2H2O(l) + O

2(g) → 4[Au(CN

2)]–(aq) + 4OH–(aq)

(i) Name the type of bond formed between the gold ions and the

cyanide ions.

____________________________________________________ [1]

(ii) This process was simulated in the laboratory. Calculate the volume

of 2 M potassium cyanide solution needed to extract 1 kg of gold

from its ore.

______________________________________________________

______________________________________________________

____________________________________________________ [3]

(b) Cyanogen, C2N

2, is a colourless gas with the characteristic smell of

bitter almonds.

(i) Draw a dot and cross diagram to show the bonding in cyanogen.

[2]

(ii) State and explain the shape of the cyanogen molecule.

______________________________________________________

______________________________________________________

____________________________________________________ [2]

(iii) Cyanogen may be prepared by warming potassium cyanide

solution with copper(II) sulphate to form copper(II) cyanide.

Decomposition of copper(II) cyanide yields copper(I) cyanide and

cyanogen.

Write the equation for the decomposition of copper(II) cyanide.

____________________________________________________ [2]









(c) Ethanenitrile may be prepared by boiling an alcoholic solution of

potassium cyanide with iodomethane.

(i) Write the equation for the formation of ethanenitrile.

____________________________________________________ [1]

(ii) Assuming this occurs as a single step nucleophilic substitution

reaction, suggest the structure of the transition state formed.

[1]

(iii) Name the reagents required to bring about the following changes.

A __________________________

B __________________________

C __________________________ [3]

CH3CH2NH2

A←⎯ CH3CN

←⎯

⎯

←⎯

⎯

CH3COOH

CH3COONa

B

C





[Turn over

(d) Potassium thiocyanate is prepared by boiling potassium cyanide

solution with sulphur. It is extremely soluble in water and reacts readily

with silver nitrate solution to form a precipitate of silver thiocyanate.

This reaction may be used, as follows, to determine the chloride content

in cheese.

Weigh out accurately approximately 1.5 g of cheese into a conical flask. Add 10 cm3 of water, 25.0 cm3 of 0.05 M silver nitrate solution (an excess) and 10 cm3 of concentrated nitric acid. Boil for 10 minutes. Cool and add a further 50 cm3 of water. The excess silver nitrate is determined by titration with standard potassium thiocyanate solution using an iron(III) indicator. At the end-point the aqueous iron(III) ions react with excess thiocyanate ions.

(i) Explain the term standard solution.

____________________________________________________ [1]

(ii) State the colour observed at the end-point.

____________________________________________________ [1]

(iii) State the formula of the iron(III) complex formed at the end-point.

____________________________________________________ [1]

(iv) Write the equation for the reaction between aqueous solutions

of silver nitrate and potassium thiocyanate to form the silver

thiocyanate precipitate.

____________________________________________________ [1]





(v) In an experiment 1.48 g of cheese was analysed as above. The

excess silver nitrate required 14.3 cm3 of 0.05 M potassium

thiocyanate solution for complete reaction. Calculate the chloride

content, in grams, per gram of cheese.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

____________________________________________________ [4]





15 Patients suffering from Parkinson’s disease have a deficiency of the brain

neurones that produce the neurotransmitter dopamine.

(a) Explain why dopamine should be very soluble in water.

__________________________________________________________

_______________________________________________________ [2]

(b) Dopamine is a base which behaves as a primary amine.

(i) Compare and suggest an explanation for the relative basic strengths

of dopamine, ammonia and phenylamine.

______________________________________________________

______________________________________________________

______________________________________________________

____________________________________________________ [3]

(ii) Write an equation for the reaction of dopamine with hydrochloric

acid.

____________________________________________________ [1]

CH2HO

dopamineHO

CH2

NH2





(c) Treatment of Parkinson’s disease often involves the use of L-dopa

which is the natural precursor of dopamine.

L-dopa

(i) Deduce the molecular formula of L-dopa.

____________________________________________________ [1]

(ii) Explain why L-dopa is optically active.

______________________________________________________

____________________________________________________ [2]

(iii) Draw the structure of the dipolar ion (zwitterion) formed when

L-dopa is dissolved in water.

[1]

CH2HO

HO

CH

COOH

NH2





ADVANCEDGeneral Certifi cate of Education

2007

MARKSCHEME


assessing

Module 5: Analytical, Transition Metals andFurther Organic Chemistry

[A2C21]






Quality of Written Communication:

2 marks The candidate expresses ideas clearly and fl uently through well-linked sentences and paragraphs. Arguments are generally relevant and well-structured. There are few errors of grammar, punctuation and spelling.

1 mark The candidate expresses ideas clearly, if not always fl uently. Arguments may sometimes stray from the point. There may be some errors of grammar, punctuation and spelling, but not such as to suggest a weakness in these areas.

0 marks The candidate expresses ideas satisfactorily, but without precision. Arguments may be of doubtful relevance or obscurely presented. Errors in grammar, punctuation and spelling are suffi ciently intrusive to disrupt the understanding of the passage.





Section A

1 C

2 D

3 D

4 B

5 C

6 D

7 C

8 B

9 B

10 B


Section A 20





Section B

11 (a) C3H7+ [1]/CH2CHO+ [1]

CH3CO+ [1] [2]

(b) C O/carbonyl [1]

(c) CH3CH2CH2COCH3 /CH3CH2CH2CH2CHO [1] 4

12 (a) (i) sodium nitrite [1] hydrochloric acid [1] [2]

(ii) diazonium ion formed is unstable/prevent decomposition [1]

(b) (i)

��

�

��

each error [–1] [2]

(ii) conjugated system/delocalised electrons/chromophore [1] absorbs visible radiation/light/energy levels close together/ to promote electrons (to a higher level) [1] Penalise inclusion of emission [–1] [2] 7

13 (a) (i) loss of electrons [1]

(ii) green [1] to red-brown/yellow/violet [1] 2Fe2+ + Cl2 → 2Fe3+ + 2Cl– [1] [3]

(iii) 1s22s22p63s23p63d6 [1] 1s22s22p63s23p63d5 [1] [2]

(iv) iron(III) more stable due to half-fi lled d (sub)shell [1]

(v) dissolve in conc. hydrochloric acid [1] add H2O2/conc. nitric acid to oxidise iron(II)/Fe [1] add (excess) potassium thiocyanate solution [1] obtain concentration from absorbance/transmission (using calibration curve) [1] [4]






(b) (i) [Co(CH3COO)2(H2O)4] [2]

(ii) oxidising agent/to oxidise [1] cobalt(II) to cobalt(III) [1] [2]

(iii) octahedral [1]

(iv) six/6 [1]

(v) 1 dm3 of peroxide produces 20 dm3 of oxygen gas = 20/24 mole oxygen = 0.833 mole = 0.833 mol dm–3

2:1 ratio ∴ 1.67 mol dm–3 [3]

(c) (i) Co2+ → Co3+ + e– or reversible equation [1] ClO– + H2O + 2e– → Cl– + 2OH– [1] 4OH– → 2H2O + O2 + 4e– [1] [3]

(ii) (homogeneous) catalyst and chlorate ions each in solution/same phase [1] 26

14 (a) (i) coordinate/dative [1]

(ii) 1 mole Au ≡ 2 moles cyanide 1000 g Au = 5.076 moles 5.076 moles Au ≡ 10.152 moles cyanide volume of 2M potassium cyanide = 10.152 × 1000/2 = 5076 cm3 or 5.076 dm3 [3]

(b) (i)

each error [–1], e.g. using all crosses [2]

(ii) linear [1] electrons move as far apart as possible [1] [2]

(iii) 2Cu(CN)2 → 2CuCN + C2N2 Unbalanced = [1] [2]

(c) (i) CH3I + KCN → CH3CN + KI [1]

(ii)

[1]









(iii) A = lithium aluminium hydride/lithium tetrahydridoaluminate [1] B = hydrochloric acid [1] C = sodium hydroxide (solution) [1] [3]

(d) (i) known concentration [1]

(ii) (blood) red [1]

(iii) [Fe(SCN)(H2O)5]2+ [1]

(iv) AgNO3 + KSCN → AgSCN + KNO3 [1]

(v) moles of excess thiocyanate = 14.3 × 0.05/1000 = 0.000715 moles of excess silver nitrate = 0.000715 moles of silver nitrate at start = 25.0 × 0.05/1000 = 0.00125 moles of silver nitrate reacting with chloride = 0.00125 – 0.000715 = 0.000535 mass of chloride in cheese = 0.000535 × 35.5 = 0.019 g mass in 1 g = 0.019/1.48 = 0.01284 g

or

volume of silver nitrate solution required to react with chloride = 25 – 14.3 = 10.7 cm3

moles = 10.7 × 0.05/1000 = 0.000535 mass of chloride in cheese = 0.000535 = 0.000535 × 35.5 = 0.019 g mass in 1 g = 0.019/1.48 = 0.01284 g

Award [4] directly for correct answer Each error [–1], carry error through [4] 23

15 (a) forms hydrogen bonds [1] between NH2 group and water [1] [2]

(b) (i) strongest: dopamine weakest: phenylamine [1] dopamine – electrons pushed towards nitrogen/lone pair more available [1] phenylamine – electrons withdrawn by aromatic ring/less available [1] [3]

(ii)

��

��

��

��

��

� ��

��

��

��

��

[1]

(c) (i) C9H11O4N [1]

(ii) carbon atom joined to 4 different [1] atoms or groups [1] [2] or (two) non superimposable [1] mirror images [1]





(iii)

��

��

��

�

�

��

[1] 10

Section B 70

Total 90





TIME

1 hour 30 minutes.




Answer all sixteen questions.




Answer all six questions in Section B. Write your answers in the





question 14(a)(iii).In Section A all questions carry equal marks, i.e. two marks for each

question.





2008

Chemistry


assessing


Organic Chemistry

[A2C21]










Section A



1 Which one of the following is the electronic structure for the iron(III) ion in the ground state?

A 1s22s22p63s23p63d5

B 1s22s22p63s23p64s13d4

C 1s22s22p63s23p64s13d5

D 1s22s22p63s23p64s23d3

2 Which one of the following is the spin-spin splitting pattern in the n.m.r. spectrum of ethyl

ethanoate?

A singlet, doublet, triplet

B singlet, quartet, triplet

C triplet, doublet, triplet

D triplet, quartet, triplet

3 Which one of the following peaks in the mass spectrum of pentane is the base peak?

10 20 30

A

B

CD

40 50 60 70 m/e

relative

abundance





[Turn over

4 Which one of the following is the strongest base?

A NH3

B NH4

+

C CH3NH

2

D CH3NH

3+

5 Which one of the following molecules contains a chromophore?

6 Which one of the following analytical techniques depends upon vibrational frequencies of

bonds?

A infra-red spectroscopy

B n.m.r. spectroscopy

C u.v. spectroscopy

D visible spectroscopy

7 In the complex ion, [MCl2(NH

3)4]+, which one of the following is the identity of M and its

associated oxidation state?

A Ag +1

B Cu +2

C Cr +3

D Mn +7

O

C HA

O

C OB

NH2C

N ND





[Turn over

8 The mechanism for the conversion of benzene to nitrobenzene is described as

A electrophilic addition.

B electrophilic substitution.

C free radical substitution.

D nucleophilic addition.

9 A sample of sodium chlorate(V) on heating produced 120 cm3 of oxygen, measured at 20 °C

and one atmosphere pressure.

2NaClO3(s) ➝ 2NaCl(s) + 3O

2(g)

How many moles of sodium chlorate(V) decomposed?

A 0.167 × 10–3 mol

B 0.250 × 10–3 mol

C 1.67 × 10–3 mol

D 3.33 × 10–3 mol

10 Using the infra-red absorption frequencies,

C–H broad 2853 – 2962 cm–1

C=O strong 1680 – 1750 cm–1

O–H strong 2500 – 3300 cm–1

C–O strong 1200 – 1400 cm–1

it is possible to identify the following spectrum:

as that of

A ethanoic acid.

B ethanol.

C propan-1-ol.

D propanone.

4000 3000 2000 5001000

wave-number (cm–1)

1500

100

0

transmittance (%)

C









[Turn over

Section B


11 A mixture of concentrated nitric and sulphuric acids forms a nitrating

mixture, which is used to nitrate benzene.

(a) Write the equation for the reaction between nitric acid and sulphuric

acid to form a nitronium ion.

______________________________________________________ [2]

(b) Explain how nitric acid is acting as a Brønsted base in this reaction.

______________________________________________________ [1]

(c) Explain why sulphuric acid may be regarded as a catalyst in this

reaction.

_________________________________________________________

______________________________________________________ [1]

⎯⎯⎯→+ HNO3 NO2 + H2OH2SO4





12 The chelating ligand edta has the following structure:

(a) Explain the term chelating and state the shape of the complex which

edta forms with magnesium ions.

_________________________________________________________

______________________________________________________ [2]

(b) Explain how standard edta solution may be used to determine the

concentration of magnesium ions in solution, naming the indicator and

stating the colour change.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

______________________________________________________ [4]

OH

OH

C

C

CN

O

OH2C

CH2

O

O

CH2

HO CH2 CH2

CH2

N

HO C









A2C2S8 3539 8 [Turn over

13 The determination of iron in its ores is an example of the application of

manganate(VII) titrations. Before titration with manganate(VII) ions any

iron(III) must be reduced to iron(II). This reduction can be carried out with

zinc amalgam (a mixture of zinc and mercury).

(a) (i) Write the equation for the reaction between zinc and iron(III) ions.

__________________________________________________ [1]

(ii) The use of the zinc amalgam prevents the further reduction of

iron(II) to iron. Use the electrode potentials above to explain why,

in theory, zinc would also reduce iron(II) to iron.

_____________________________________________________

__________________________________________________ [1]

(b) A mixture of iron(II) and iron(III) sulphates was analysed as described

above. The mixture was dissolved in water and made up to 1.0 dm3.

It was found that 25.0 cm3 of this solution needed 21. 6 cm3 of 0.1 M

acidified potassium manganate(VII) solution to reach the end point.

After reduction of a separate 25.0 cm3 of the solution by zinc amalgam,

22.8 cm3 of the 0.1 M acidified potassium manganate(VII) solution

were required.

(i) What colour change is observed at the end point?

__________________________________________________ [2]

(ii) Write the equation for the reaction between iron(II) ions and

acidified manganate(VII) ions.

__________________________________________________ [2]

Zn2+(aq) + 2e– Zn(s) E = –0.76 V

Fe3+(aq) + e– Fe2+(aq) E = +0.77 V

Fe2+(aq) + 2e– Fe(s) E = –0.44 V









(iii) Using the first titration figure, calculate the number of moles of

iron(II) ions present in the 1.0 dm3 solution.

_____________________________________________________

__________________________________________________ [1]

(iv) What mass of iron(II) sulphate was present in the mixture?

__________________________________________________ [1]

(v) Using the second titration figure, calculate the total mass of

iron(III) sulphate present in the mixture.

_____________________________________________________

_____________________________________________________

_____________________________________________________

__________________________________________________ [3]





[Turn over

14 The transport of some proteins through the body may be assisted by

cobalt(II) ions.

(a) (i) Protein structure is described as primary, secondary or tertiary.

Explain these terms.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

__________________________________________________ [3]

(ii) Name two functional groups in a protein which allow it to bond to

metal ions such as cobalt(II).

_____________________________________________________

__________________________________________________ [2]

(iii) Hydrolysis of proteins yields amino acids which can be

separated by two-way chromatography. Explain how two-way

chromatography could be used to separate a mixture of the four

amino acids glycine, alanine, threonine and leucine.

Describe how the presence of leucine in the mixture could be

confirmed.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

__________________________________________________ [4]










(b) Threonine has a zwitterion (dipolar ion) structure.

(i) Explain the term chiral and mark any chiral centres in threonine

with an asterisk (*).

_____________________________________________________

__________________________________________________ [3]

(ii) Explain how the zwitterion (dipolar ion) is formed.

__________________________________________________ [1]

(iii) Explain why threonine has a high melting point.

_____________________________________________________

__________________________________________________ [2]

(iv) Write an equation for the reaction between threonine and nitrous

acid.

__________________________________________________ [2]

(v) Suggest what will be observed if a solution of threonine is added to

nitrous acid.

__________________________________________________ [1]

CH3

CH

CH C

O

O–+H3N

OH









15 Amines may be prepared by the reduction of nitriles or by the reaction of

ammonia with alkyl halides.

(a) 1-bromobutane reacts with ammonia (by a similar mechanism to that of

the alkaline hydrolysis of haloalkanes) to form 1-aminobutane.

(i) Name the mechanism.

__________________________________________________ [1]

(ii) Write an equation for the reaction.

__________________________________________________ [1]

(iii) Describe the mechanism for the reaction.

_____________________________________________________

_____________________________________________________

__________________________________________________ [3]

(b) 1-aminobutane may also be prepared by the reduction of butanenitrile.

(i) Name a suitable reducing agent.

__________________________________________________ [1]

(ii) Using [H] to represent the reducing agent write an equation for the

reduction of butanenitrile.

__________________________________________________ [2]

[Turn overwww.franklychemistry.co.uk




(c) Nitriles may undergo acid or base catalysed hydrolysis.

(i) Explain the term hydrolysis.

_____________________________________________________

__________________________________________________ [1]

(ii) Draw a labelled enthalpy level diagram, using the axes below,

to illustrate the uncatalysed and the acid catalysed hydrolysis of

butanenitrile. Assume the reaction is exothermic.

[3]

(iii) Write the equation for the reaction of butanenitrile with aqueous

sodium hydroxide.

__________________________________________________ [2]





16 Malachite has the formula CuCO3.Cu(OH)

2, and can be readily converted to

copper(II) oxide by heating. The oxide can be reduced to copper by heating

strongly with carbon.

(a) (i) What is the percentage of copper in malachite?

_____________________________________________________

_____________________________________________________

__________________________________________________ [3]

(ii) Write an equation for the action of heat on malachite.

__________________________________________________ [2]

(iii) Write an equation for the reduction of copper(II) oxide by carbon.

__________________________________________________ [1]

(b) Malachite dissolves in nitric acid to form copper(II) nitrate solution.

The dropwise addition of excess ammonia solution produces colour

changes.

(i) State and explain the observations on adding ammonia solution,

giving the formulae of the copper compounds or complex(es)

formed.

_____________________________________________________

_____________________________________________________

_____________________________________________________

__________________________________________________ [4]

[Turn overwww.franklychemistry.co.uk




(ii) State and explain the colour change observed on adding

concentrated hydrochloric acid to the final solution in part (i), giving the formula of the copper complex formed.

_____________________________________________________

__________________________________________________ [2]

(iii) Explain these ligand replacement reactions in terms of the overall

stability constants.

_____________________________________________________

_____________________________________________________

__________________________________________________ [3]






2008

MARKSCHEME


assessing


[A2C21]






Section A

1 A

2 B

3 B

4 C

5 D

6 A

7 C

8 B

9 D

10 D [20] 20

Section A 20





Section B

11 (a) HNO3 + 2H2SO4 → NO2+ + H3O

+ + 2HSO4– [2]

(b) removes protons from H2SO4 [1]

(c) regenerated [1] 4

12 (a) binding or complexation of a multidentate ligand [1] donates more than one pair of electrons/more than one coordination bond [1] octahedral [1] (any two from three) [2]

(b) titrate known volume of Mg2+ solution [1] Buffer to pH 10 [1] indicator [1] eriochrome black solachrome black Colour change [1] (eriochrome) red to blue (solachrome) red to blue ratio (edta to Mg2+) is 1:1 [1] (any four from five) [4] 6

13 (a) (i) Zn + 2Fe3+ → + 2Fe2+ + Zn2+ [1]

(ii) DE

φ

= +0.32 (so reaction should proceed) [1]

(b) (i) colourless to pink [2]

(ii) 5Fe2+ + MnO4– + 8H+ → Mn2+ + 5Fe3+ + 4H2O [2]

(iii) mole of manganate(VII) solution 21.6 × 0.1 × 10–3

= 2.16 × 10–3

= 0.00216 in 25 cm3 moles of Fe2+ = 0.00216 × 5 = 0.0108 in 1 dm3 moles of Fe2+ = 40 × 0.0108 = 0.432 mol [1]

(iv) FeSO4 = 56 + 32 + 64 = 152 mass iron(II) sulphate = 0.432 × 152 g = 65.66 g [1]

(v) volume of manganate(VII) solution ≡ iron(III) ions = 22.8 – 21.6 = 1.2 cm3 moles of manganate(VII) = 1.2 × 0.1 × 10–3

= 1.2 × 10–4

moles of Fe2+ = 5 × 1.2 × 10–4

= 6 × 10–4 mol

moles of Fe2+ in 1 dm3

= 40 × 6 × 10–4 mol = 2.4 × 10–2 mol









Fe2(SO4)3 = 2 × 56 + 3 × 32 + 12 × 16 = 112 + 96 + 192 = 400

2Fe3+ ≡ 1 Fe2(SO4)3 ∴ 1.2 × 10–2 = 0.012 mol Fe2(SO4)3

Mass of iron(III) sulphate = 0.012 × 400 = 4.8 g [3] 11

14 (a) (i) Primary structure is the order of its amino acids [1] secondary structures: alpha-helix or beta-pleated sheet [1] tertiary structure is the (full 3-dimensional) folded structure of the polypeptide chain [1] [3]

(ii) COOH/COO– [1] NH2 [1] [2]

(iii) place mixture at origin of chromatographic paper or plate develop using solvent 1 [1] turn paper of plate through 90˚ and develop using solvent 2 [1] locate spots using (ninhydrin) [1] Comparison of Rf values for leucine [1] [4]


(b) (i)

Four different groups attached to a carbon atom [1] [3]

(ii) Transfer of H+ from COOH to NH2 [1]

(iii) Strong attraction between + and – charges [2]

(iv)

[2]

(v) bubbles (of nitrogen) [1] 20

CH3

* CH — OH

+H3N — CH — C — O–

* O [2]

CH3

CHOH

NH2 — CH — COOH + HNO2 →

CH3

CHOH

HO — CH — COOH + N2 + H2O





15 (a) (i) nucleophilic substitution [1]

(ii) C4H9Br + NH3 → C4H9NH2 + HBr or C4H9NH3+ Br– [1]

(iii) δ+ δ– C —Br polarised

lone pair on • •N/

• •N H3 attracted to

δ+C

bond formed C—N, bond broken C—Br [3]

(b) (i) lithal [1]

(ii) C3H7CN + 4 [H] → C3H7CH2NH2 [2]

(c) (i) reaction with water to split the molecule [1]

(ii)

(reaction coordinate) [3]

(iii) C3H7CN + NaOH + H2O → C3H7CO2Na + NH3 [2] 14

16 (a) (i) CuCO3.Cu(OH)2 = 222 % Cu = 128/222 × 102 = 57.7% [3]

(ii) CuCO3.Cu(OH)2 → 2CuO + H2O + CO2 [2]

(iii) CuO + C → Cu + CO [1] or 2CuO + C → 2 Cu + CO2

(b) (i) Cu(OH)2, [Cu(NH3)4(H2O)2] 2+ [2]

blue → deep blue [2] [4] ppt (solution)

(ii) [CuCl4]2– [1]

blue → green/yellow [1] [2]

enthalpy

products

reactants

uncatalysed

catalysed





(iii) The overall stability constant is simply the equilibrium constant for the total reaction:

[Cu(H2O)6]2+ + 4NH3 [Cu(H2O)2(NH3)4]2+ + 2H2O [1]

is given by this expression:

overall Kstab = [Cu(NH3)4(H2O)2

2+][Cu(H2O)6

2+][NH3]4 [1]

which is large, so the formation of the product is favoured.

It is generally true that the higher the stability constant of a complex, the more readily the product (in this case [Cu(H2O)2(NH3)2]2+), forms [1]

The second reaction,

[Cu(H2O)2(NH3)4]2+ + 4Cl– [CuCl4]2- + 2H2O + 4NH3 [1]

…has an overall Kstab which again is large therefore yellow [CuCl4]2– forms readily [1]

To a maximum of [3] [3] 15

Section B 70

Total 90









TIME

1 hour 30 minutes.




Answer all sixteen questions.




Answer all six questions in Section B. Write your answers in the





question 15(f)(vi).In Section A all questions carry equal marks, i.e. two marks for each

question.





2009

Chemistry


assessing


Organic Chemistry

[A2C21]










Section A



1 Which one of the following is the electronic structure of the Co2+ ion in the ground state?

3d 4s

A [Ar]

B [Ar]

C [Ar]

D [Ar]

2 Which one of the following gives the order of increasing basic strength for ammonia, ethylamine and phenylamine?

A ammonia, phenylamine, ethylamine B ethylamine, ammonia, phenylamine C phenylamine, ammonia, ethylamine D phenylamine, ethylamine, ammonia

3 Which one of the following statements describes the primary structure of a protein?

A The folding of the α-helix. B The formation of a β-pleated sheet. C The sequence of amino acids. D The coiling of the chains.

4 The mechanism for the bromination of benzene is described as

A electrophilic addition. B electrophilic substitution. C nucleophilic addition. D nucleophilic substitution.





5 20 cm3 of a hydrocarbon CxHy were exploded in excess oxygen. The total volume of gases

after reaction was found to be 50 cm3 lower than at the start. On bubbling through sodium

hydroxide solution a further contraction of 80 cm3 occurred, all measurements were at 20 °C

and one atmosphere pressure. The formula of the hydrocarbon was

A C2H

4

B C2H

6

C C4H

6

D C4H

8

6 Iodoethane may be converted to propylamine by reaction with

A ammonia.

B ammonia followed by lithal, LiAlH4.

C potassium cyanide followed by ammonia.

D potassium cyanide followed by lithal, LiAlH4.

7 The fertiliser ammonium sulphate is manufactured according to the equation:

H2SO

4(aq) + 2NH

3(g) → (NH

4)2SO

4(aq)

Which one of the following mixtures will produce the greatest mass of ammonium sulphate?

(1 tonne = 1000 kg)

mass of sulphuric acid/tonne mass of ammonia/tonne

A 4 6

B 5 5

C 8 2

D 9 1

8 Which one of the following nickel complexes is the most stable?

A [Ni(H2O)

6]2+

B [Ni(NH3)6]2+

C [Ni(en)3]2+

D [Ni(edta)]2–





9 Which one of the following reagents will not produce a precipitate when a few drops are

added to separate samples of iron(III) sulphate solution?

A ammonia solution

B barium chloride solution

C potassium thiocyanate solution

D sodium hydroxide solution

10 Which one of the following processes does not involve any redox reactions?

A Decomposition of OCl– ions using Co2+ ions.

B Determination of magnesium ions in solution using edta.

C Determination of the percentage of iron in aluminium foil.

D Preparation of potassium dichromate from chromium(III) ions.





Section B


11 (a) Complete the flow scheme below by writing the formulae of the three

compounds formed.

[3]

(b) Copper(II) sulphate solution reacts with aqueous barium nitrate to form

a white precipitate. Write the equation for this reaction.

_______________________________________________________[1]

12 The mass spectrum of 2-chloropropane, CH3CHClCH

3, is shown below.

(a) (i) Suggest why two molecular ion peaks are present in the spectrum.

_____________________________________________________

___________________________________________________[1]

Cu2+(aq)conc. HCl

excess NH3(aq)

NaOH(aq)

m/z

Rel

ativ

e In

tensi

ty

10

0

20

40

60

80

100

20 30 40 50 60 70 80





(ii) State the formula for the species giving rise to the peak at

m/e = 63.

___________________________________________________[1]

(b) The n.m.r. spectrum of 2-chloropropane contains two sets of peaks as

shown below.

(i) Explain the peak integration.

_____________________________________________________

___________________________________________________[2]

(ii) Explain the chemical shifts.

_____________________________________________________

___________________________________________________[1]

(iii) Explain the splitting pattern a.

_____________________________________________________

_____________________________________________________

___________________________________________________[1]

(iv) Explain why b is a doublet.

_____________________________________________________

_____________________________________________________

___________________________________________________[1]

5 4 3 2 1 0

b

a

a









13 Vanadium is a characteristic transition metal showing variable oxidation states and catalytic action.

(a) The following change occurs when a solution containing VO2+ ions is

shaken with zinc amalgam.

VO2+(aq) → VO2+(aq)

Deduce the oxidation state of vanadium in each of the two species and hence state the role of the zinc amalgam in the reaction.

VO2+ ________________

VO2+ ________________

_______________________________________________________[3]

(b) Vanadium pentoxide is used as a solid heterogeneous catalyst in the Contact process, catalysing the conversion of sulphur dioxide to sulphur trioxide.

2SO2(g) + O2(g) 2SO3(g)

(i) Explain the term heterogeneous.

___________________________________________________[1]

(ii) Explain in terms of surface chemistry how the vanadium pentoxide catalyses the above reaction.

_____________________________________________________

_____________________________________________________

___________________________________________________[2]





(c) Vanadium(III) sulphate dissolves in water to form a green solution.

(i) State the formula of vanadium(III) sulphate.

___________________________________________________[1]

(ii) Suggest the formula of hydrated vanadium(III) ions in aqueous

solution and state the shape of this complex ion.

_____________________________________________________

___________________________________________________[2]





14 In the 19th century, used tea leaves were often recycled by boiling with

iron(II) sulphate and sheep dung before being coloured with compounds

such as Prussian Blue.

(a) Prussian Blue, KFe[Fe(CN)6], may be prepared by adding potassium

ferrocyanide solution, K4[Fe(CN)

6], to a suitable aqueous iron salt.

(i) Identify the ions present in potassium ferrocyanide solution.

___________________________________________________[2]

(ii) Suggest a suitable iron salt to react with potassium ferrocyanide in

the preparation of Prussian Blue.

___________________________________________________[1]

(b) Drinks made with this “recycled” tea contained aqueous iron(II) ions.

The concentration of iron(II) ions in solution can be determined by

titration with standard potassium manganate(VII) solution.

MnO4

–(aq) + 5Fe2+(aq) + 8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)

(i) State the colour change noted at the end point of the titration.

___________________________________________________[2]

(ii) Calculate the volume of 0.1 M potassium manganate(VII) solution

required to react with 25.0 cm3 of a solution which contains 7.84 g

of iron(II) ions per litre.

_____________________________________________________

_____________________________________________________

_____________________________________________________

___________________________________________________[3]





(c) Iron(II) sulphate and ammonium sulphate combine to form the double

salt iron(II) ammonium sulphate, FeSO4.(NH

4)2SO

4.6H

2O.

(i) Describe how a back titration may be used to determine the

percentage of ammonia in a sample of ammonium sulphate (details

of calculations are not required). You may assume all apparatus

used is clean and dry.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

___________________________________________________[4]

(ii) Suggest why this method would be unsuitable for determining the

percentage of ammonia in the double salt.

_____________________________________________________

___________________________________________________[2]

(iii) Calculate the mass of iron(II) sulphate required to make 20.0 g of

the double salt.

_____________________________________________________

_____________________________________________________

___________________________________________________[3]





[Turn over

15 Aromatic chemistry is a branch of organic chemistry which includes those compounds with 6-membered ring structures such as benzene and methylbenzene (toluene), C6H5CH3.

(a) Name the industrial source of benzene.

_______________________________________________________[1]

(b) State the empirical formula of benzene.

_______________________________________________________[1]

(c) Describe the bonding present in benzene.

_________________________________________________________

_________________________________________________________

_______________________________________________________[3]

(d) Benzene may be converted to methylbenzene (toluene) by reaction with chloromethane in the presence of aluminium chloride.

C6H6 + CH3Cl → C6H5CH3 + HCl

The mechanism is similar to that for the nitration of benzene.

(i) Suggest the function of the aluminium chloride.

___________________________________________________[1]

(ii) Suggest the formula of the species which attacks the benzene ring.

___________________________________________________[1]









(e) Nitration of benzene forms nitrobenzene, C6H

5NO

2.

(i) Name the reagents used for the nitration of benzene.

_____________________________________________________

___________________________________________________[2]

(ii) Further nitration results in the formation of dinitrobenzene. Draw

and name the structure of one of the three possible isomers of

dinitrobenzene.

[2]

(iii) State the reagents and conditions for the reduction of nitrobenzene

to phenylamine.

_____________________________________________________

_____________________________________________________

___________________________________________________[3]





(f) Phenylamine reacts with a mixture of sodium nitrite and hydrochloric acid to form benzene diazonium chloride. The benzene diazonium ion forms a scarlet precipitate of azo-2-naphthol when added to an alkaline solution of 2-naphthol.

(i) Sodium nitrite and hydrochloric acid react to form nitrous acid in situ. Write the equation for this reaction.

___________________________________________________[1]

(ii) Draw the structure of the benzene diazonium ion.

[2]

(iii) Explain why ethylamine does not form such a diazonium ion.

_____________________________________________________

___________________________________________________[1]

(iv) Name the type of reaction between benzene diazonium chloride and 2-naphthol to form the azo-2-naphthol.

___________________________________________________[1]

(v) Deduce the molecular formula of azo-2-naphthol.

___________________________________________________[1]

OH

2-naphthol





(vi) Explain, in terms of electron transitions, why azo dyes are coloured.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

___________________________________________________[3]






16 Kevlar is used to make bullet-proof vests. The first step in its production is

the polymerisation of the two monomers shown below:

(a) State how infra-red spectroscopy could be used to distinguish between

the two monomers.

_________________________________________________________

_______________________________________________________[2]

(b) Write an equation for the reaction between benzene-1,4-dicarboxylic

acid and excess sodium carbonate solution.

_______________________________________________________[2]

(c) (i) Draw the structure of the dimer formed between the two

monomers.

[1]

(ii) Name the link formed between the two monomers.

___________________________________________________[1]

(iii) Kevlar is a very strong and rigid material. Suggest why this

polymer exhibits such properties.

_____________________________________________________

___________________________________________________[2]

HOOCNH2H2N COOH

benzene -1,4-diamine benzene -1,4-dicarboxylic acid






2009

Chemistry



[A2C21]

WEDNESDAY 27 MAY, MORNING

MARKSCHEME





Section A

1 A

2 C

3 C

4 B

5 C

6 D

7 C

8 D

9 C

10 B


Section A 20









[Turn over

Section B

11 (a) [Cu(NH3)4(H2O)2]2+

[CuCl4]2– Cu(OH)2 [1] each [3]

(b) CuSO4 + Ba(NO3)2 → Cu (NO3)2 + BaSO4 [1] 4

12 (a) (i) (Two) isotopes of chlorine [1]

(ii) CH3CH35Cl+ [1]

(b) (i) Peak integration

1:6 ratio [1] reference to hydrogens (in each environment) [1] [2]

(ii) Chemical shift

peak A shifted downfield due to (electronegative) chlorine [1]

(iii) Spin-spin splitting Signal at a split (into 7) due to 6 (equivalent) neighbouring H [1]

(iv) Signal at b is a (doublet) due to 1 neighbouring H [1] 7

13 (a) VO2+ = +5 [1]

VO2+ = +4 [1] reducing agent/provide electrons [1] [3]

(b) (i) (catalyst and reactants in) different phases [1]

(ii) gas molecules adsorb/bond to surface [1] weakens bonds/lowers activation energy/d-orbitals/orientation [1] [2]

(c) (i) V2(SO4)3 [1]

(ii) [V(H2O)6]3+ [1] Octahedral [1] [2] 9





14 (a) (i) K+ [1] [Fe(CN)6]4– [1] [2]

(ii) Any soluble iron(III) salt, e.g. sulphate, chloride, nitrate [1]

(b) (i) colourless to pink/purple [1] [2]

(ii) moles of iron per litre = 7.84/56 = 0.14 moles of iron in 25 cm3 = 0.14/40 = 3.5 × 10–3

moles MnO4– = 3.5 × 10–3/5 = 7 × 10–4

volume = 7 × 10–4 × 1000/0.1 = 7 cm3

[–1] for each error, carry error through [3]

(c) (i) use known mass of sample (and dissolve to make 250 cm3 solution) [1] known excess [1] of NaOH [1] titrate (25 cm3) portions of above with (standard) hydrochloric acid [1] [4]

(ii) iron(II) ions [1] would form a precipitate (of iron(II) hydroxide)/react with NaOH [1] [2]

(iii) RFM FeSO4 = 152 RFM FeSO4.(NH4)2SO4.6H2O = 392 moles double salt = 20/392 = 0.051 moles of iron(II) sulphate = 0.051 mass of iron(II) sulphate = 0.051 × 152 = 7.75 g each error [–1], carry error through [3] 17

15 (a) petroleum [1]

(b) CH [1]

(c) single/sigma (covalent) bonds( carbon – carbon and carbon – hydrogen) [1] delocalised electrons (above and below plane of ring [1], form pi-bond/overlapping P orbitals [1] bond order of 1.5 between carbon atoms/C–C bond length all equal [1] Any three from four [3]

(d) (i) catalyst [1]

(ii) CH3+ [1]





[Turn over

(e) (i) concentrated sulphuric acid [1] concentrated nitric acid [1] [2]

(ii) structure = [1] name = [1] 1,2– or 1,3– or 1,4–dinitrobenzene [2]

(iii) tin [1] concentrated hydrochloric acid [1] sodium hydroxide [1]

reflux [1] [3]

(f) (i) NaNO2 + HCl → HNO2 + NaCl [1]

(ii)

each error [–1], e.g. missing charge/double bond, etc. [2]

(iii) too unstable [1]

(iv) coupling [1]

(v) C16H12N2O [1]

(vi) conjugated/delocalised electrons/chromophore [1] absorb visible light/radiation [1] to promote electrons (to higher energy level) [1] mention of emission = [–1] [3] Quality of written communication [2] 25

16 (a) look for N–H or C–N (stretch/bend) peaks [1]– benzene–1,4–diammine [1] or C–O/C=O/O–H stretch/bend peaks [1]– benzene–1,4–dicarboxylic acid [1] or one has N–H/peak and the other a C–O/C=O/O–H peak [1] [2]

(b)

[2]

(c) (i) [1]

(ii) peptide [1]

(iii) (strong) hydrogen bonds [1] between different chains [1] [2] 8

Section B 70

Total 90

N+ N

HOOC COOH + Na2CO

3 → NaOOC COONa + H

2O + CO

2

COOHH2N N

H

C

O

2 from 3






2010


assessing

Analytical, Transition Metals, Electrochemistryand Further Organic Chemistry

[AC222]

TUESDAY 1 JUNE, AFTERNOON

TIME

2 hours.


Write your Centre Number and Candidate Number in the spaces provided at the top of this page.Answer all seventeen questions.Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering.Answer all seven questions in Section B. Write your answers in the spaces provided in this question paper.


The total mark for this paper is 120.Quality of written communication will be assessed in question 16(b).In Section A all questions carry equal marks, i.e. two marks for each question.In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question.A Periodic Table of Elements (including some data) is provided.

New

Specifi

catio

n









Section A

For each of the following questions only one of the lettered responses (A–D) is correct.


1 The mass spectrum of methanol is shown below. Which one of the following is the base peak?

2 Which one of the following represents the electronic configuration for the Fe3+ ion?

A 1s2 2s2 2p6 3s2 3p6 3d5

B 1s2 2s2 2p6 3s2 3p6 3d3 4s2

C 1s2 2s2 2p6 3s2 3p6 3d4 4s1

D 1s2 2s2 2p6 3s2 3p6 3d6 4s2

3 Which one of the following formulae cannot be determined by colorimetry?

A [Cu(NH3)4(H2O)2]2+

B [Fe(SCN)(H2O)5]2+

C [Ni(NH3)4(H2O)2]2+

D [Zn(NH3)4(H2O)2]2+

100%

Relativeintensity

25 30

m/e

35

A

B

C

D





4 The standard electrode potentials for a series of redox equations are listed below.

E /V

Mn2+(aq) + 2e– Mn(s) –1.19

Fe2+(aq) + 2e– Fe(s) –0.44

Ni2+(aq) + 2e– Ni(s) –0.25

I2(s) + 2e– 2I–(aq) +0.54

Fe3+(aq) + e– Fe2+(aq) +0.77

Ag+(aq) + e– Ag(s) +0.80

Which one of the elements listed will reduce Fe3+(aq) to Fe2+(aq), but not to Fe(s)?

A Iodine B Manganese C Nickel D Silver

5 Which one of the following represents the structure of cisplatin?

Pt

Cl

NH3

NH3

Cl

A

Pt

Cl

NH3

NH3

H2O

H2O

D

Cl

Cl

NH3

NH3

B

Pt

Cl

NH3

NH3

C

Pt





6 The nmr spectrum of a compound X is shown below.

Which one of the following is X?

A CH3CH2CH2COOH B CH3CH2COOCH2CH3 C CH3COOCH2CH3 D CH3CH2COOH

7 A green solid was dissolved in water and the resulting solution divided into two portions. Sodium hydroxide solution was added to one of the portions and ammonia solution to the

other. The results are summarised in the table below.

Solution added Few drops of solution Excess solution

Sodium hydroxide solution Green precipitate No effect

Ammonia solution Green precipitate Dissolves to form a blue solution

Which one of the following ions was present in the green solid?

A Cr3+

B Cu2+

C Fe2+

D Ni2+

8 Which one of the following is the colour of chrome alum crystals?

A Black B Green C Orange D Violet

5 4 3 2 1 0Chemical shift, d





9 25.0 cm3 of hydrogen peroxide solution were added to excess acidified potassium iodide solution and the resulting solution made up to 500 cm3.

25.0 cm3 of the diluted solution reacted with 36.4 cm3 of sodium thiosulphate solution of concentration 0.10 mol dm–3.

Which one of the following is the concentration of the undiluted hydrogen peroxide?

A 0.07 mol dm–3

B 0.15 mol dm–3

C 1.46 mol dm–3

D 2.91 mol dm–3

10 Which one of the following pairs of monomers will not combine to form a polymer?

A HOOC(CH2)4COOH and H2N(CH2)6NH2 B H2N(CH2)6NH2 and H2N(CH2)6NH2 C CH2CH2 and CH2CH2 D HOOC(CH2)4COOH and HO(CH2)2OH




[Turn over

Section B

Answer all seven questions in this section

11 (a) Complete the table below by giving the name of the indicator and the colour change at the end point.

Titration IndicatorColour change

from to

Edta added to magnesium ions

Thiosulphate ionsadded to iodine

[6]

(b) Some iron tablets, used to treat anaemia, contain iron(II) fumarate (FeC4H2O4).

Five of these iron tablets were dissolved in dilute sulphuric acid and the solution made up to 250 cm3 with distilled water. On titration

25.0 cm3 of this solution reacted with 18.7 cm3 of 0.01 mol dm–3 acidified potassium manganate(VII) solution.

(i) Write the equation for the reaction of iron(II) ions with acidified manganate(VII) ions.

__________________________________________________ [2]

(ii) What is the colour change at the end point of the titration?

From _________________ to __________________ [2]

(iii) Calculate the mass of iron(II) fumarate in each tablet.

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

__________________________________________________ [4]









12 (a) Polythene is a typical addition polymer.

(i) State the conditions necessary for the formation of HD polythene.

Temperature: ________________________________________

Pressure: ___________________________________________

Catalyst: __________________________________________ [3]

(ii) Making reference to their structures, explain the difference in flexibility between HD and LD polythene.

___________________________________________________

___________________________________________________

_________________________________________________ [2]

(b) Polyethylene terephthalate is a polyester.

(i) Draw the repeating unit for polyethylene terephthalate.

[2]

(ii) Give one use for polyethylene terephthalate.

_________________________________________________ [1]




13 Transition metals form complex ions with ligands.

(a) Explain what is meant by the term polydentate ligand.

_______________________________________________________

_____________________________________________________ [2]

(b) The complex below is formed when dimethylglyoxime is added to a solution of hydrated nickel(II) ions.

(i) What is the co-ordination number of the nickel(II) ion?

_________________________________________________ [1]

(ii) Suggest the shape around the central nickel(II) ion.

_________________________________________________ [1]

(iii) What type of bonds in the complex are represented by each of the following?

________________________________________________

----- ________________________________________________

______________________________________________ [3]

H3C

C N N

N NC

H3C

CH3

CH3

C

C

Ni2+

O O

O O

H

H




(c) Explain in terms of entropy why dimethylglyoxime displaces the water ligands in the hydrated nickel(II) ion to form the nickel(II) dimethylglyoxime complex.

_______________________________________________________

_______________________________________________________

_____________________________________________________ [2]




[Turn over

14 The explosive trinitrotoluene (TNT) is prepared by the nitration of methylbenzene (toluene).

(a) Suggest a systematic name for TNT.

_____________________________________________________ [1]

(b) TNT burns to form a mixture of carbon dioxide, nitrogen and water.

Write an equation for the complete combustion of TNT.

_____________________________________________________ [2]

(c) TNT is prepared from toluene by using the same nitrating mixture as is used to nitrate benzene.

(i) Name the acids present in the nitrating mixture.

_________________________________________________ [2]

(ii) Write an equation for the formation of the nitrating species.

_________________________________________________ [2]

(iii) What name is given to the nitrating species?

_________________________________________________ [1]

NO2 NO2

NO2

CH3

TNT

CH3

Toluene




(d) The mechanism for nitrating toluene is similar to that for nitrating benzene.

(i) What name is given to this mechanism?

_________________________________________________ [2]

(ii) Draw the mechanism for the mononitration of toluene.

[2]

(e) 4-nitrotoluene can be converted to toluidine.

(i) Name the reagents which could be used to convert 4-nitrotoluene to toluidine.

____________________________________________________

__________________________________________________ [2]

(ii) A salt of toluidine is formed during the reduction. How can toluidine be liberated from this salt?

__________________________________________________ [1]

CH3

NH2

Toluidine




[Turn over

(f) Toluidine is used in the manufacture of dyes. The first step in the process is to convert the toluidine to its diazonium

ion using nitrous acid.

(i) Write an equation for the formation of nitrous acid from sodium nitrite.

__________________________________________________ [1]

(ii) What conditions are necessary for the reaction between toluidine and nitrous acid to form the diazonium ion?

__________________________________________________ [1]

(iii) Write an equation for the conversion of toluidine to its diazonium ion.

__________________________________________________ [2]

(g) One dye is made by reacting the toluidine diazonium ion with phenol.

(i) What name is given to this type of reaction?

__________________________________________________ [1]

(ii) Draw the structure of the dye formed.

[2]

(iii) Explain why this dye is coloured.

____________________________________________________

____________________________________________________ ____________________________________________________

_________________________________________________ [3]









[Turn over

15 Vanadium and chromium are typical transition metals.

(a) Explain, in terms of electronic structure, what is meant by a transition metal.

_______________________________________________________

_____________________________________________________ [1]

(b) Vanadium(V) oxide acts as a heterogeneous catalyst in the conversion of sulphur dioxide to sulphur trioxide in the manufacture of sulphuric acid.

(i) Write the equation for the conversion of sulphur dioxide to sulphur trioxide.

_________________________________________________ [1]

(ii) What is meant by a heterogeneous catalyst?

_________________________________________________ [1]

(iii) Explain, in terms of chemisorption, how vanadium(V) oxide acts as a catalyst in this reaction.

___________________________________________________

___________________________________________________

___________________________________________________

_________________________________________________ [3]




(c) An acidified solution of ammonium vanadate(V) undergoes a series of reductions when it is stirred with zinc.

(i) Complete the table below, giving the colour of VO2+(aq) and V3+(aq) formed at the different stages of the reduction.

Ion Colour

VO2(aq) Yellow

VO2+(aq)

V3+(aq)

V2+(aq) Violet

[2]

(ii) Chromium will also reduce ammonium vanadate(V).

E /VCr3+(aq) + 3e– Cr(s) –0.74

VO2(aq) + 2H+(aq) + e– VO2+(aq) + H2O(l) +1.00

Write an equation for the reaction between chromium and VO2(aq) ions and calculate the e.m.f. of the reaction.

___________________________________________________

e.m.f. ____________________________________________ [3]

+

+

+




(d) Potassium chromate(VI), K2CrO4 can be prepared by oxidising a solution of chromium(III) ions.

(i) Name a suitable oxidising agent.

_________________________________________________ [1]

(ii) Give the colour change on oxidising the chromium(III) ions to chromate(VI) ions.

from: _______________________________________________

to: _______________________________________________ [2]

(iii) Chromate(VI) and dichromate ions are involved in the following equilibrium:

2CrO42– (aq) + 2H+(aq) Cr2O7

2–(aq) + H2O(l)

State and explain the colour change when sodium hydroxide solution is added to this equilibrium.

___________________________________________________

___________________________________________________

_________________________________________________ [3]




16 The burning sensation felt when eating chilli peppers is caused by capsaicin.

(a) Capsaicin is used in pepper sprays at a concentration of 5% by mass per volume (5 g in 100 cm3).

(i) What is the molecular formula of capsaicin?

_________________________________________________ [1]

(ii) Calculate the concentration of capsaicin in mol dm–3 of the pepper spray.

___________________________________________________

___________________________________________________

_________________________________________________ [3]

(b) A sample of capsaicin extracted from chilli peppers will contain a large number of organic impurities.

Describe how you would use two-way paper chromatography to show that the sample contained capsaicin.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_____________________________________________________ [4]


CH2 CH2

CH2 CH2H3C N

HHO

O C

O

CH2

CH

CH3

CH3

CH

CH

Capsaicin




17 Proteins are formed from amino acids.

(a) (i) Describe the primary, secondary and tertiary structure of proteins.

Primary: ____________________________________________

_________________________________________________ [1]

Secondary: __________________________________________

_________________________________________________ [2]

Tertiary: ____________________________________________

_________________________________________________ [2]

(ii) Explain why some proteins can act as enzymes.

___________________________________________________

___________________________________________________

_________________________________________________ [2]

(iii) Explain why the efficiency of most enzymes is lowered at 60 °C.

___________________________________________________

_________________________________________________ [2]

(b) Aspartic acid and asparagine are amino acids.

COOH COOH

H

H2NOC C

H

NH2 NH2

HOOC C

Aspartic acid Asparagine

(i) Suggest how aspartic acid could be converted to asparagine.

_________________________________________________ [1]







(ii) Write an equation for the reaction between aspartic acid and asparagine to form a dipeptide.

_________________________________________________ [2]

(iii) Amino acids dissolve in water to form a dipolar ion (zwitterion).

Draw the structure of the dipolar ion formed by asparagine.

[1]

(iv) Complete the following flow diagram to show the structure of the organic product formed.

[4]

COOH

H

NH2

H2NOC CHCl Na2CO3

C2H5OH

SOCl2





2010

MARKSCHEME

New

Specifi

catio

n


assessing

Analytical, Transition Metals, Electrochemistry and Further Organic Chemistry

[AC222]TUESDAY 1 JUNE, AFTERNOON




Section A

1 C

2 A

3 D

4 C

5 B

6 C

7 D

8 D

9 C

10 B


Section A 20




Section B

11 (a)

[1] for the correct indicator [1] for the correct colour change [6]

(b) (i) MnO4– + 8H+ + 5Fe2+ → Mn2+ + 4H2O + 5Fe3+

Formulae [1], balancing [1] [2]

(ii) Colourless [1] to pink [1] [2]

(iii) Moles of MnO4– = (18.7 × 0.01)/1000 = 1.87 × 10–4

Moles of FeC4H2O4 in 25 cm3 = (1.87 × 10–4) × 5 = 9.35 × 10–4

Moles of FeC4H2O4 in 250 cm3 = 9.35 × 10–3

Mass of FeC4H2O4 = (9.35 × 10–3) × 170 = 1.59 g

Mass of FeC4H2O4 in 1 tablet = 1.59/5 = 0.318 g

(4 marks, [–1] for each mistake) [4] 14

12 (a) (i) Temperature: 20–75 °C [1] Pressure: 1–25 atmospheres [1] Catalyst: Ziegler/titanium(IV) chloride and triethylaluminium [1] [3]

(ii) High density: (little branching/high crystallinity)/low flexibility or Low density: (high branching/low crystallinity)/high flexibility [2]

(b) (i)

2 marks ([–1] for each mistake) [2]

(ii) e.g. clothing/plastic bottles [1] 8

Titration IndicatorColour change

from to

Magnesium/Edta Eriochrome black T Red Blue

Iodine/Thiosulphate Starch Blue/Black Colourless

OCH2CH2OOC CO




13 (a) Polydentate ligand: a ligand with more than one lone pair of electrons which forms more than one central bond (with a coordinate/dative metal) [2]

(b) (i) 4 [1]

(ii) Square planar [1]

(iii) : Covalent bond [1] ----- : Hydrogen bond [1] : Dative/Co-ordinate bond [1] [3]

(c) (dimethylglyoxime) replaces 6 water molecules/ or 3 molecules → 7 molecules. [1] This increases the overall entropy [1] [2] 9

14 (a) methyl –2, 4, 6 – trinitrobenzene [1]

(b) 2C7H5N3O6 + 10 or O2 → 14CO2 + 3N2 + 5H2O


(c) (i) Concentrated nitric acid [1] and concentrated sulphuric acid [1] [2]

(ii) HNO3 + 2H2SO4 → NO2+ + 2HSO4

– + H3O+


(iii) Nitronium ion [1]

(d) (i) Electrophilic [1] substitution [1] [2]

(ii)

([–1] for each mistake) [2]

(e) (i) Tin [1] in (concentrated) hydrochloric acid [1] [2]

(ii) Addition of alkali to the salt [1]

([–1] for each mistake)

CH3 CH3 CH3

+ NO2+

NO2

H

NO2

+ H+

212

12




(f) (i) NaNO2 + HCl → HNO2 + HCl (ii) Below 10°C [1]

(iii)


(g) (i) Coupling [1] (ii)


(iii) Conjugated (double bonds)/Delocalised/Energy levels close together [1] Hence electron excited/move to higher energy level [1] Removes a colour from light [1] [3] 25

15 (a) Transition metal atoms/ions have an incomplete d-subshell. [1]

(b) (i) 2SO2 + O2 → 2SO3 [1]

(ii) It is in a different physical state from the reactants. [1]

(iii) Reactants adsorb onto the surface [1] Bonds weakened in the reactants [1] Bonds form in products and products are desorbed from the surface [1] Orientation/closer together/lower activation energy [1] Any 3 from 4 [3]

(c) (i)

([1] each) [2]

Ion Colour

VO2+ (aq)

VO2+ (aq) Blue

V3+ (aq) Green

V2+ (aq)

H3C N N OH

H3C NH2 + HNO2 → H3C N N + OH– + H2O+




(ii) 3VO2+(aq) + 6H+(aq) + Cr(s) → 3VO2+(aq)

+ 3H2O (l) + Cr3+ (aq)

Formulae [1], balancing [1]

e.m.f. +1.74 V [1] [3]

(d) (i) Hydrogen peroxide [1]

(ii) Green [1] to yellow [1] [2]

(iii) Colour change from orange to yellow [1] H+ ions will be removed [1] Equilibrium moves to the left [1] [3] 17

16 (a) (i) C18H27O3N [1]

(ii) 100 cm3 contain 5 g 1000 cm3 contain 50 g

= 0.164 mol dm–3 [3]

(b) Place sample at the corner of a chromatogram [1] Run the chromatogram in a suitable solvent [1] (Dry chromatogram and) run at right angles in a different solvent [1] Development + Compare Rf values or chromatogram run with capsaicin [1] Quality of written communication [2] [6] 10

17 (a) (i) Primary: sequence of amino acids [1] Secondary: alpha helix/beta pleated sheet [1] due to the formation of a hydrogen bond between the nitrogen of one peptide bond and the oxygen of another further along the chain [1] Tertiary: cross links between amino acids [1] due to H-bonds between amino acids/electrostatic attractions between polar groups/ dipole–dipole interactions/Van der Waals forces between non-polar groups/disulphide bridges [1] [5]

(ii) The enzyme provides an active site [1]/lock and key mechanism [1] [2]

(iii) High temperature denatures the enzyme [1] the structure and the active site is no longer functional [1] (disrupts the secondary and tertiary structures by breaking bonds [1]) Any two [2]

50305




(b) (i) React with ammonia and heat the ammonium salt [1]

(ii)


(iii)

[1]

NH2

C

H

CONH2

C

H

HOOC COOH + H2N COOH

NH2

H

O||

H CONH2

H

HOOC C C N C COOH + H2O

NH3+

C

H

H2NOC COO–




(iv)

or

([1] each) [4] 17

Section B 100

Total 120

NH2

C

H

H2NOC COCl–

NH2

C

H

HOOC COOH

NH2

C

H

H2NOC COO–Na+

NH2

C

H

H2NOC COOC2H5

NH3+Cl–

C

H

H2NOC COOH





2011

Chemistry



[AC222]

FRIDAY 27 MAY, AFTERNOON

TIME

2 hours.


Write your Centre Number and Candidate Number in the spaces provided at the top of this page.Answer all fifteen questions.Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering.Answer all five questions in Section B. Write your answers in the spaces provided in this question paper.


The total mark for this paper is 120.Quality of written communication will be assessed in question 13(d)(iii).

In Section A all questions carry equal marks, i.e. two marks for each question.In Section B the figures printed down the right-hand side of pages indicate the marks awarded to each question or part question.A Periodic Table of Elements (including some data) is provided.

111319









[Turn over

Section A

For each of the questions only one of the lettered responses (A–d) is correct.


1 Chlorine has two isotopes, chlorine-35 and chlorine-37. Which one of the following is the number of peaks found in the mass

spectrum of chlorine gas?

A 2 B 3 C 4 d 5

2 The mechanism for the nitration of benzene is described as

A electrophilic addition. B electrophilic substitution. C nucleophilic addition. d nucleophilic substitution.

3 Copper(II) ions form a coloured complex with the ligand L. The following absorbances were recorded on mixing different volumes of 0.05 M copper(II) sulfate and 0.1 M ligand L.

volume of 0.05 M CuSO4(aq)/cm3

volume of 0.1 M L(aq)/cm3 absorbance

3.0 7.0 0.412

4.0 6.0 0.457

5.0 5.0 0.406

6.0 4.0 0.335

7.0 3.0 0.251

Which one of the following is the cation to ligand ratio in this complex?

A 1:2 B 1:3 C 2:3 d 3:2









4 In which one of the following is a metal in the +2 state?

A [Ag(nH3)2]

B [Co(nH3)5Br]2

C K4Fe(Cn)6 d K2Cr2O7

5 An organic compound X contains carbon, hydrogen and oxygen only. When 1.29 g of X is burnt completely, 3.30 g of carbon dioxide and 1.35 g of water are formed. Which one of the following is the empirical formula of X?

A CH2O B C2H6O C C4H8O d C5H10O

6 Which one of the following is the relative molecular mass of 2,4-dichloro-3,5-dimethylphenol?

A 190 B 191 C 192 d 196

7 Given the following standard electrode potentials:

E

φ

/V V3(aq) e V2(aq) 0.26 SO4

2(aq) 2H(aq) 2e SO32(aq) H2O(l) 0.17

VO2(aq) 2H(aq) e V3(aq) H2O(l) 0.34 Fe3(aq) e Fe2(aq) 0.77 VO2

(aq) 2H(aq) e VO2(aq) H2O(l) 1.00

Which one of the following reagents will convert V3+(aq) to VO2+(aq)?

A Aqueous iron(II) ions B Aqueous iron(III) ions C Aqueous sulfate ions in acidic solution d Aqueous sulfite ions




8 Which one of the following is the volume of water which must be added to 30.0 cm3 of 0.25 mol dm3 sulfuric acid to produce 0.05 mol dm3 sulfuric acid?

A 30 cm3

B 120 cm3

C 150 cm3

d 270 cm3

9 Which one of the following is the total number of electrons involved in bonding in benzene?

A 12 B 18 C 24 d 30

10 The concentration of aqueous magnesium ions may be determined by titration with standard edta using Eriochrome Black T as indicator. Which one of the following is the colour change at the end point?

A Blue to green B Blue to red C Red to blue d Red to green




Section B

Answer all five questions in the spaces provided.

11 Lysine (2,6-diaminohexanoic acid) has the formula

H2n(CH2)4CH(nH2)COOH

The molecule is optically active and may undergo polymerisation.

(a) (i) Explain the term optically active.

�� [2]

(ii) draw the 3d structure of lysine labelling the asymmetric carbon with an asterisk (*).

[2]

(b) Explain why lysine has a relatively high melting point.

��

��

�� [2]

(c) Write the formula of the organic ion present when lysine is dissolved in an alkaline solution.

�� [1]




[Turn over

(d) draw the structure of a dimer formed when two molecules of lysine react.

[2]

(e) A mixture of amino acids may be separated using paper chromatography.

(i) Explain the term Rf value as applied to paper chromatography.

�� [1]

(ii) Explain, in terms of partition, what a low Rf value indicates about a particular amino acid.

��

�� [2]

(f) An amino acid was found to have the following composition by mass:

element % composition

n 10.5

C 36.1

H 5.3

O 48.1

deduce the empirical formula for this amino acid.

��

��

��

�� [3]









12 Chromium is a transition metal which was discovered by Louis Vauquelin in 1797. He was able to detect traces of chromium in precious gems, such as ruby and emerald.

(a) State the electronic structure of a chromium atom and explain why the arrangement is stable.

��

�� [2]

(b) Chromium(III) oxide, Cr2O3, can be reduced to the metal by heating with aluminium powder according to the equation:

2Al(s) Cr2O3(s) 2Cr(s) Al2O3(s)

Calculate the percentage yield when 42.5 g of chromium are obtained from a reaction between 25 g of aluminium and 100 g of chromium(III) oxide.

��

��

��

��

�� [3]

(c) Chromium trioxide, CrO3, is formed by the reaction between excess concentrated sulfuric acid and a concentrated solution of potassium dichromate. Potassium sulfate and water are formed as by-products.

Write the equation for this reaction.

�� [2]




(d) A data book lists the following standard electrode potentials:

Cr3(aq) e Cr2(aq) 0.41 V Ag(aq) e Ag(s) 0.80 V

(i) Cr2 can reduce silver ions to silver atoms. Write the equation for this reduction.

�� [1]

(ii) Deduce the electrode potential for this change.

�� [1]

(e) Chrome alum is a double salt prepared by the reduction of potassium dichromate, K2Cr2O7, using a suitable reducing agent.

(i) Name a suitable reducing agent.

�� [1]

(ii) State the colour and formula of crystalline chrome alum.

��

�� [2]

(f) Chrome alum may be used as a mordant in dyeing, binding the dye molecules to the fibre. The dye Prontosil is prepared by the following sequence:

H2NSO

2NH

2

AH

2NSO

2N

2� Cl�

NH2

NH2

Prontosil

4-aminobenzenesulfonamide

(i) Deduce the empirical formula for 4-aminobenzenesulfonamide.

�� [1]




(ii) name the reagents required for step A.

�� [1]

(iii) State and explain the condition necessary for the first step.

��

�� [2]

(iv) Suggest a structure of the dye Prontosil which is formed by a coupling reaction.

[2]

(v) Explain why Prontosil is coloured.

��

��

��

�� [3]




13 The first person to extract ethanoic acid from vinegar was the alchemist Jabir ibn Hayyan Geber (c. 721–815 AD). However the pure compound was not produced for another ten centuries.

(a) The mass spectrum of ethanoic acid shows a distinct peak at m/e 59. State the formula of the species giving rise to this peak.

�� [1]

(b) Ethanoic acid reacts with ethanol to form the ester ethyl ethanoate, CH3COOC2H5. The n.m.r. spectrum of ethyl ethanoate consists of three sets of peaks as shown below.

10 9 8 7 6 5 4 3 2 1 0

d (ppm)

a b

(i) Explain the peak integrations.

��

��

�� [2]

(ii) Explain the chemical shifts.

��

��

�� [2]




(iii) Explain the splitting pattern a.

��

�� [1]

(iv) Explain why b is a singlet.

��

�� [1]

(c) Ethanoic acid can be converted to ethanamide via the thermal decomposition of the ammonium salt.

(i) Write the equation for the reaction of ethanoic acid with ammonia.

�� [1]

(ii) Write the equation for the thermal decomposition.

�� [1]

(iii) Ethanamide is hydrolysed by either hydrochloric acid or sodium hydroxide to form different organic products. State the formula of the organic product in each case.

hydrochloric acid ��

sodium hydroxide �� [2]




(d) Ethanamide can be converted to an amine in the following sequence.

A BCH3CONH2 CH3CN CH3CH2NH2

(i) Give the formula of reagents A and B.

A ��

B �� [2]

(ii) Write the equation for the reaction of an unknown amine, RNH2, with ethanoyl chloride.

�� [1]

(iii) Describe how you would identify the unknown amine using the pure N-substituted amide. Include relevant practical steps.

��

��

��

��

��

��

�� [4]

Quality of written communication. [2]

(e) 1,2-diaminoethane (en) is a bidentate ligand forming stable complex ions with transition metal ions.

(i) Explain the term bidentate.

��

�� [2]




(ii) Hexaaquanickel(II) ions react with en in solution. Write the equation for this reaction in which all the water ligands are replaced.

�� [2]

(iii) Explain why this ligand replacement takes place.

��

�� [2]




14 Iron is a transition metal which fulfils vital biological, industrial and chemical roles.

(a) The most common oxidation states of iron in its compounds are 2 and 3. State the electronic structures of the Fe2 and Fe3 ions.

Fe2 ��

Fe3 �� [2]

(b) Metallic iron is used as a heterogeneous catalyst in the Haber Process to make ammonia.

N2(g) 3H2(g) 2NH3(g)

Explain in terms of chemisorption how the reaction takes place.

��

��

�� [3]

(c) Iron filings are used to catalyse the monohalogenation of aromatic compounds such as methylbenzene, C6H5CH3.

(i) Draw a flow scheme for the mechanism of the monobromination of methylbenzene to form 4-bromomethylbenzene.

[3]

(ii) Suggest the name of the product formed in the monobromination of 1,4-dimethylbenzene.

�� [2]




(d) (i) Explain the role of iron(II) in haemoglobin.

��

�� [2]

(ii) Explain the effect of the inhalation of carbon monoxide on haemoglobin.

�� [1]

(e) Aqueous iron(III) ions form a stable complex with the bidentate ligand ethanedioate, C2O4

2. The iron(III) ions combine with three ethanedioate ions. deduce the

formula of the complex formed.

�� [1]

(f) Potassium manganate(VII) oxidises iron(II) ions and ethanedioate ions according to the equations:

MnO 4– (aq) 5Fe2(aq) 8H(aq) 5Fe3(aq) Mn2(aq) 4H2O(l)

2MnO 4– (aq) 5C2O4

2(aq) 16H(aq) 2Mn2(aq) 10CO2(g) 8H2O(l)

(i) describe, with observations, how you could confirm the presence of aqueous iron(III) ions, following the oxidation of iron(II) ions, without interference from manganese(II) ions.

��

��

�� [3]

(ii) 25.0 cm3 of an acidified iron(II) ethanedioate solution required 32.2 cm3 of 0.025 mol dm3 of potassium manganate(VII) solution for complete reaction. Calculate the concentration, in mol dm3, of the iron(II) ethanedioate solution.

��

��

��

��

�� [4]









[Turn over

15 Polymers have become invaluable materials with many familiar names e.g. polythene, Perspex, and nylon.

(a) The manufacture of High Density (HD) polythene was first developed by Ziegler in the 1950s.

(i) State the conditions used to manufacture HD polythene.

��

��

�� [3]

(ii) State and explain the flexibility and softening temperature of HD polythene.

��

��

��

�� [3]

(b) Perspex is an addition polymer made by polymerisation of methyl 2-methylpropenoate monomer shown below.

CH2 � C — COOCH3

CH3

Draw a section of the Perspex polymer showing at least two repeating units.

[2]




[Turn over

(c) Nylon is a condensation polymer made from the two monomers 1,6-diaminohexane and hexanedioic acid.

H2N(CH2)6NH2 HOOC(CH2)4COOH

1,6-diaminohexane hexanedioic acid

(i) Explain the term condensation polymer.

��

�� [1]

(ii) Draw the repeat unit in nylon circling the peptide link in the structure.

[3]

(d) Explain why the disposal of polyesters in landfill sites is more environmentally acceptable than the similar disposal of polythene.

��

�� [2]

(e) Proteins are natural polymers which act as structural materials.

(i) State what is meant by the primary structure of a protein.

�� [1]

(ii) Proteins hydrolyse slowly in acid conditions. Suggest how enzymes work to allow the process to occur more quickly.

��

��

�� [2]










2011


assessingAnalytical, Transition Metals, Electrochemistry

and Further Organic Chemistry

[AC222]

FRIDAY 27 MAY, AFTERNOON

MARKSCHEME




[Turn over

Section A

1 D

2 B

3 B

4 C

5 D

6 B

7 B

8 B

9 D

10 C


Section A 20









Section B

11 (a) (i) ability to rotate plane [1] of plane polarised light [1] [2]

(ii)

COOH �C

NH2

(CH2)

4NH

2

*

H

correct structure (3D) [1] asymmetric carbon labelled correctly [1] [2]

(b) zwitterion/ionic [1] strong attractions between oppositely charged ions/molecules [1] [2]

(c) H2N(CH2)4CH(NH2)COO2 [1]

(d) H2N(CH2)4CH(NH2)CONH(CH2)4CH(NH2)COOH/ H2N(CH2)4CH(NH2)CONHCH(CH2)4NH2 | COOH [2]

(e) (i) distance travelled by solute divided by distance travelled by solvent (front) [1]

(ii) more soluble in water/stationary phase [1] than mobile phase/solvent [1] [2]

(f) N C H O

10.5 36.1 5.3 48.1

4RAM 0.75 3.01 5.3 3.01

40.75 1 4 7 4

empirical formula 5 C4H7O4N (each error [21], cet) [3] 15



12 (a) 1s22s22p63s23p63d54s1 [1] half-filled d subshell stable [1] [2]

(b) moles Al 5 25/27 5 0.926 moles Cr2O3 5 100/152 5 0.658 2 moles Al 5 1 mole Cr2O3 therefore Cr2O3 in excess 1 mole Al 5 1 mole Cr 0.926 mole Al 5 0.926 mole Cr mass Cr 5 0.926 3 52 5 48.15 g % yield 5 42.5 3 100/48.15 5 88.3% Award [3] for correct answer. Each error [21], carry error through [3]

(c) K2Cr2O7 1 H2SO4 K2SO4 1 2CrO3 1 H2O [2] unbalanced [21]

(d) (i) Cr21 1 Ag1 Cr31 1 Ag [1]

(ii) 0.8 2(20.41) 5 (1)1.21 (V) [1]

(e) (i) ethanol/alcohol [1]

(ii) purple/violet [1] K2SO4.Cr2(SO4)3.24H2O [1] [2]

(f) (i) C6SN2H8O2 [1]

(ii) sodium nitrite and hydrochloric acid [1]

(iii) #10 ºC [1] diazonium ion decomposes above this [1] [2]

(iv) H2NSO2 N 5 N NH

2

NH2

structure [2], each error [21] [2]

(v) highly conjugated/delocalised [1] electronic energy levels close together [1] (electron transitions) absorb visible light [1] [3] 21



13 (a) CH3COO1 [1]

(b) (i) 5 ratio 2 : 3 : 3 or 3 : 2 : 3 [1] CH3 : CH2 : CH3/no. of Hs in each environment [1] [2]

(ii) high value quartet near electronegative O lowest CH3 from CH2CH3 intermediate singlet proximity to COO all three [2] errors [21] [2]

(iii) (quartet) due to split by three chemically equivalent H (n 1 1) [1]

(iv) no H on adjacent atom (to split signal) [1]

(c) (i) CH3COOH 1 NH3 CH3COONH4 [1]

(ii) CH3COONH4 CH3CONH2 1 H2O [1]

(iii) acid: CH3COOH [1] alkaline: CH3COONa [1] [2]

(d) (i) A: P4O10 [1] B: LiAlH4 [1] [2]

(ii) RNH2 1 CH3COCl CH3CONHR 1 HCl [1]

(iii) determine melting point/description of apparatus heat slowly record temperature when melting starts and stops/range compare to tables Any four [4]

Quality of written communication [2] (e) (i) two coordinate (dative) bonds

formed by lone pairs [2]

(ii) [Ni(H2O)6]21 1 3en [Ni(en)3]21 1 6H2O [2] unbalanced [1]

(iii) increase in entropy [1] 4 particles to 7 particles [1] [2] 26



14 (a) Fe21: 1s22s22p63s23p63d6 [1] Fe31: 1s22s22p63s23p63d5 [1] [2]

(b) molecules adsorbed/attached to surface [1] weakens bonds/alignment/bonds formed with surface [1] lowers activation energy [1] [3]

(c) (i)

CH3

� � Br�

CH3

BrH

CH3

Br

� H�

Each error [21] [3]

(ii) 2-bromo-1,4-dimethylbenzene [2] Each error [21]

(d) (i) oxygen forms bond with Fe21 [1] carried around the body [1] [2]

(ii) CO combines irreversibly [1]

(e) [Fe(C2O4)3]32 [1]

(f) (i) thiocyanate ions/hydroxide ions/NH3(aq) [1] blood red/rust/brown [1] solution/ppt [1] [3]

(ii) 1 mole MnO42 5 5 moles Fe21

2 moles MnO42 5 5 moles C2O4

22

3 moles MnO42 5 5 moles FeC2O4

Number of moles iron(II) ethanedioate 5 32.2 3 0.025 1000 5 8.05 3 1024

Number of moles MnO42 5 8.05 3 1024 3

53

5 1.34 3 1023 in 25.0 cm3

Concentration MnO42 5 1.34 3 1023 3 40 5 0.0536

5 0.054 mol dm23

Award [4] directly for correct answer Each error [21], carry error through [4] 21



15 (a) (i) Ziegler Philips 50–75º 150–180º [1] 1–10 atms./low 30–40 atms. [1] TiCl4/aluminium Cr2O3 [1] (Ziegler catalyst) [3]

(ii) rigid and high softening temperature [1] little branching [1] pack close together/crystalline/strong intermolecular forces [1] [3]

(b) H CH3 H CH3 z z z z —– C —– C —– C —– C —– z z z z H COOCH3 H COOCH3

Structure [2]

(c) (i) (polymerisation involves) loss of water/small molecule [1]

(ii) H H O O z z z z z z 3—– N —– (CH2)6 —– N –— C –— (CH2)4 –— C —–4 structure [2] peptide link [1] [3]

(d) polyesters are biodegradable [1] as they can be hydrolysed [1] [2]

(e) (i) sequence of amino acids [1]

(ii) lock and key/active site [1] lowers activation energy/lower energy pathway [1] [2]

Section B

Total

17

100

120




2012

Chemistry



[AC222]


TIME

2 hours.


Write your Centre Number and Candidate Number in the spaces provided at the top of this page.Answer all seventeen questions.Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering.Answer all seven questions in Section B. Write your answers in the spaces provided in this question paper.


The total mark for this paper is 120.Quality of written communication will be assessed in question 16(c)(i).

In Section A all questions carry equal marks, i.e. two marks for each question.In Section B the figures printed down the right-hand side of pages indicate the marks awarded to each question or part question.A Periodic Table of Elements (including some data) is provided.









[Turn over

Section A

For each of the following questions only one of the lettered responses (A-D) is correct.


1 Which one of the following applies to the ligand substitution reaction shown?

[Ni(H2O)6]21 1 3en [Ni(en)3]21 1 6H2O

Change in Coordination Number �S º

A 6 to 3 negative B 6 to 3 positive C none negative D none positive

2 Which one of the following lists the compounds in order of increasing base strength?

A ethanamide, methylamine, phenylamine B ethanamide, phenylamine, methylamine C methylamine, ethanamide, phenylamine D phenylamine, ethanamide, methylamine

3 The reaction of 4-hydroxyphenylamine to produce paracetamol is shown below.

CH3COCI � � HCI

NH2

OH

N CH3C

O

OH

H

If the reaction has an 80% yield, 10.9 g of 4-hydroxyphenylamine produces

A 12.1 g of paracetamol. B 13.6 g of paracetamol. C 15.1 g of paracetamol. D 18.9 g of paracetamol.









4 Which one of the following methods may be used to separate a mixture of amino acids obtained from protein hydrolysis?

A distillation B recrystallisation C solvent extraction D thin-layer chromatography

5 Which one of the following is a correct statement about the stereochemistry of the complex [Pt(NH3)2Cl2]?

A It is square planar and has cis/trans isomers. B It is square planar and has two optical isomers. C It is tetrahedral and has cis/trans isomers. D It is tetrahedral and has two optical isomers.

6 25.0 cm3 of potassium iodate(V) solution were added to excess potassium iodide solution dissolved in sulfuric acid. The iodine liberated required 30.0 cm3 of 0.05 mol dm3 Na2S2O3 solution. Which one of the following is the concentration of the potassium iodate(V) solution?

A 0.01 mol dm3

B 0.02 mol dm3

C 0.04 mol dm3

D 0.05 mol dm3

7 Which one of the following gives the ground state electronic configuration for the copper atom and the copper(II) ion?

copper atom copper(II) ion

A 1s2 2s2 2p6 3s2 3p6 3d9 4s2 1s2 2s2 2p6 3s2 3p6 3d9 B 1s2 2s2 2p6 3s2 3p6 3d9 4s2 1s2 2s2 2p6 3s2 3p6 3d7 4s2

C 1s2 2s2 2p6 3s2 3p6 3d10 4s1 1s2 2s2 2p6 3s2 3p6 3d8 4s1

D 1s2 2s2 2p6 3s2 3p6 3d10 4s1 1s2 2s2 2p6 3s2 3p6 3d9



[Turn over

8 The diagram below shows the titration of a solution of magnesium ions with edta using Eriochrome Black T as indicator.

edta solution

magnesium ions� indicator

What is the colour change at the end point?

A blue to red B green to blue C red to green D red to blue

9 Which one of the following statements about glycine is not correct?

A It has a relatively high melting point. B It contains 32% carbon by mass. C It exists as optical isomers. D It is soluble in water.

10 Which one of the following statements about propanamide is not correct?

A It produces an M11 peak at 73 in its mass spectrum. B It can be dehydrated to form propanenitrile. C It has the molecular formula C3H7NO. D It is a weaker base than ammonia.









[Turn over

Section B

Answer all seven questions in the spaces provided.

11 The amino group is found in amines. Phenylamine is used in the synthesis of azo compounds. Consider the following sequence of steps:

N � N Cl�

NO2

A

NH3 CI�

B

NH2

C

phenol

azo compound

�

�

(a) (i) Give the names of the reagents used in the following steps.

A [2]

B [1]

C [2]

(ii) Give the conditions used in step C and name the product.

[2]

(iii) Draw the structure of the azo compound. Describe its appearance and name the compound.

[3]



(b) Amino acids, such as lysine and valine, also contain the amino group.

H2N — C — COOH

H

CH2(CH2)2NH2

Iysine

H2N — C — COOH

H

CH(CH3)2

valine

(i) Draw the zwitterion of valine.

[1]

(ii) Draw the structure of lysine when it is dissolved in an excess of a strong acid.

[2]

(iii) Draw the structures of the two dipeptides which can be formed from one molecule of glycine and one molecule of alanine. Circle the peptide link in each structure.

[3]









[Turn over

12 Standard electrode potentials can be used to predict the feasibility of reactions.

Na�(aq) � e� � Na(s) �2.71Mg2�(aq) � 2 e� � Mg(s) �2.37Al3�(aq) � 3 e� � Al(s) �1.66Zn2�(aq) � 2 e� � Zn(s) �0.76Cr3�(aq) � e� � Cr2�(aq) �0.412H�(aq) � 2 e� � H2(g) 0.00Fe3�(aq) � e� � Fe2�(aq) �0.77

E º /V

(a) Define the term standard electrode potential.

[3]

(b) From the table, select the species which is the most powerful reducing agent.

[1]

(c) Write the equation for the reaction of aluminium with aqueous zinc ions and calculate the e.m.f.

[3]



(d) Under standard conditions, the e.m.f. of the cell shown below is 10.32 V.

Zn2�(aq)

ZincSalt

bridge Iron

Fe2�(aq)

V

Calculate the standard electrode potential for the iron half-cell.

[1]



13 Nuclear magnetic resonance spectroscopy (nmr) is an important analytical technique.

(a) In the question below, draw one possible structure for each of the compounds A, B, C and D.

(i) Compounds A and B are isomers with the molecular formula C4H8O2. Both have a triplet, a singlet and a quartet in their nmr spectrum.

A B

[2]

(ii) Compound C has the molecular formula C6H12 and has only one peak in its nmr spectrum.

[1]

(iii) Compound D has the molecular formula C5H13N. It is a tertiary amine with three types of chemically equivalent hydrogen atom which exist in the ratio of 6:6:1 and produce a doublet in the nmr spectrum.

[1]



(b) Mass spectrometry is another important analytical technique.

2-chloropropanoic acid produces molecular ion peaks at 108 and 110. It also produces a significant fragment peak at 91.

(i) Suggest why there are two molecular ion peaks.

[2]

(ii) Identify the fragment ion.

[2]

(iii) Complete the table giving the integration values and the splitting of each peak in the nmr spectrum of 2-chloropropanoic acid:

Peak 1 Peak 2 Peak 3

Integration 3

Splitting singlet

[4]



[Turn over

14 Iron(II) ions are part of the structure of haemoglobin. Many people supplement their diet by taking “iron tablets” which contain hydrated iron(II) sulfate, FeSO4.7H2O.

(a) “Iron tablets” with a total mass of 8.00 g were dissolved in dilute sulfuric acid and the solution was made up to 250 cm3 in a volumetric flask. 25.0 cm3 portions of this solution were titrated with 0.02 mol dm3 acidified potassium manganate(VII). The average titre was found to be 24.0 cm3.

(i) Write the equation for the reaction of acidified manganate(VII) ions with iron(II) ions.

[2]

(ii) What is the colour change at the end point of this titration?

[2]

(iii) Calculate the percentage of hydrated iron(II) sulfate in the tablets.

[5]



(b) The [Fe(H2O)6]31 ion behaves as a Brønsted acid by the loss of one hydrogen ion.

(i) Write an equation to show [Fe(H2O)6]31 behaving as a Brønsted acid.

[2]

(ii) Write the expression for the acid dissociation constant of the [Fe(H2O)6]31 ion.

[1]

(iii) What is observed when sodium hydroxide solution is added to a solution containing [Fe(H2O)6]31 ions?

[2]

(iv) Describe a different chemical test, including observations, which can be used to detect the presence of low concentrations of [Fe(H2O)6]31 ions. Give the formula of any new complex formed.

[4]

(c) With reference to the iron(II) ions in haemoglobin, explain why breathing carbon monoxide can result in death.

[2]



[Turn over

15 Benzene is toxic and carcinogenic, however, the reactions of aromatic compounds can be studied in the laboratory using other substances such as methyl benzoate.

(a) The electrons in the bonds in benzene are delocalised. Draw two structures for benzene to show the p-orbitals before and after delocalisation.

before after

[2]

(b) Nitration of methyl benzoate can be achieved using a “nitrating mixture” of concentrated nitric and sulfuric acids.

(i) Write an equation to show how these two acids react when mixed.

[2]

(ii) Name the ion, produced in this reaction, which attacks the methyl benzoate molecule.

[1]

(iii) Draw a flow scheme to show the mechanism of the mononitration of methyl benzoate and name the mechanism.

Name of mechanism [4]



(iv) Name the organic product of this reaction.

[1]

(v) Describe the appearance of this organic product.

[2]



[Turn over

16 Transition metals form coloured complex ions and exist in a range of oxidation states.

(a) In terms of electron structures, explain why zinc is not a transition metal.

_____________________________________________________________

_____________________________________________________________

___________________________________________________________ [2]

(b) The VO21 ion can be reduced to V21 using zinc in the presence of an

acid. Zinc is oxidised to form Zn21 ions.

(i) Write a half-equation for the reduction of VO21 to V21.

[2]

(ii) Combine the above half-equation with the following oxidation half-equation:

Zn Zn21 1 2e

to give the ionic equation for the reaction.

[2]

(iii) When this reduction is carried out in the laboratory a series of colour changes are observed. Complete the following table:

Ion Colour

VO21

Blue

Green

V21

[4]



(c) Potassium dichromate (K2Cr2O7) can be prepared by the oxidation of a chromium(III) salt such as hydrated chromium(III) chloride, CrCl3.6H2O.

(i) Describe the preparation of potassium dichromate from hydrated chromium(III) chloride. Include all observations.

[6]


(ii) When 13.33 g of hydrated chromium(III) chloride were used, 2.93 g of potassium dichromate were obtained. Calculate the percentage yield.

[4]



[Turn over

17 Polymers are long chain molecules produced by addition or condensation reactions. Polyesters and polyamides are the two main types of condensation polymer.

(a) The polyamide nylon-6,6 is made by a condensation reaction between 1,6-diaminohexane and hexanedioic acid. Draw a section of the polymer showing two repeating units.

[3]

(b) The repeating unit of the polymer PET is shown below:

O

C

O

C O OCH2

CH2

(i) Draw the structure of the smaller of the two monomers.

[1]

(ii) Name this monomer.

[1]



(c) Kevlar is a polyamide used in bulletproof jackets. A section of the polymer chain is shown below:

N

H

N

H

N

H

N

H

O

C

O

C

O

C

O

C

(i) How many repeating units are shown?

[1]

(ii) Give the structures of the two monomers which can be used to produce Kevlar.

[2]

(d) A section of an addition polymer is shown below:

C

CH3

C C C

H CH2

H CH2

CH3

CH3

CH3

CH3

CH3

Name the monomer used to produce this polymer.

___________________________________________________________ [2]




2012




[AC222]


MARKSCHEME



Section A

1 D

2 B

3 A

4 D

5 A

6 A

7 D

8 D

9 C

10 A


Section A 20



Section B

11 (a) (i) A tin/concentrated hydrochloric acid [2] B sodium hydroxide [1]

C sodium nitrite/hydrochloric acid [2] [5]

(ii) 0–10°C [1] benzenediazonium chloride [1] [2]

(iii)

OHN

[1]

orange solid [1] 4-hydroxyazobenzene/4-hydroxyphenylazobenzene [1] [3]

(b) (i)

H

C COO

CH(CH3)2

+H3N

[1]

(ii) H

C COOH

CH2(CH2)2NH3

+H3N

+

[2]

(iii)

NH2N C

H

C

H

O H H

C

CH3

COOH

NH2N C

H

C

CH3

O H H

C

H

COOH

[3] 16



[Turn over

12 (a) The potential difference [1] measured when a half-cell is connected to a hydrogen electrode [1] under standard conditions [1] [3]

(b) Na(s) [1]

(c) 2Al + 3Zn2+ → 2Al3+ + 3Zn [2] –0.76 – (–1.66) + 1.66 – 0.76 = +0.90 V [1] [3] (d) +0.32 = x – (–0.76) –0.44 V [1] 8

13 (a) (i)

O

O CC

H

H H

H

H CC

H

H

H

O

O C

H

H

H CC

H

H

H

H

H

C

[2] (ii) H

C

H

CH

HC

C

C

C H

HHH

H

H

H

H

CCH3

CH3H3C

C

H3C

or

[1]

(iii)

C

N CH3H3C

CH3 H

CH3

[1]

(b) (i) 2 isotopes [1] of chlorine [1] or 35Cl and 37Cl [1] [2]

(ii) C3H435ClO+ [2]

(iii) Peak 1 Peak 2 Peak 3

1 [1] 1 [1]Doublet [1] Quartet [1]

[4] 12



14 (a) (i) MnO4– + 8H+ + 5Fe2+ → Mn2+ + 4H2O + 5Fe3+ [2]

(ii) colourless to pink [2]

(iii) moles of manganate(VII) = 0.00048 moles of iron(II) in 25 cm3 = 0.0024 moles of iron(II) in 250 cm3 = 0.024 mass of FeSO4.7H2O = 0.024 × 278 = 6.672 g % hydrated iron(II) sulfate = 83.4% [5] Each error [–1]

(b) (i) [Fe(H2O)6]3+ ? [Fe(OH)(H2O)5]

2+ + H+ [2]

(ii) Ka =

[Fe(OH)(H2O)52+][H+]

[Fe(H2O)63+]

[1]

(iii) a rust/brown [1] precipitate [1] [2]

(iv) (potassium) thiocyanate solution [1] blood red [1] solution [1] [Fe(SCN)(H2O)5]2+ [1] [4]

(c) CO forms a very strong bond with the iron(II) ion in haemoglobin [1] this prevents the transportation of oxygen [1] [2] 20



[Turn over

15 (a)

before after [2]

(b) (i) HNO3 + 2H2SO4 → NO2+ + H3O+ + 2HSO4

– [2]

(ii) nitronium ion [1]

(iii) C

NO2

C

+ H

O OCH3

++ NO2

H

CO OCH3

NO2

+

O OCH3

[3]

electrophilic substitution [1] [4]

(iv) methyl 3-nitrobenzoate [1]

(v) cream [1] solid [1] [2] 12

orC

NO2H

O OCH3

+



16 (a) Does not have an incomplete d-subshell in its (stable) ion [1] Zn2+ is 3d10 [1] [2]

(b) (i) VO2+ + 4H+ + 3e– → V2+ + 2H2O [2]

(ii) 2VO2+ + 8H+ + 3Zn → 2V2+ + 4H2O + 3Zn2+ [2]

(iii) Ion ColourVO2

+ Yellow [1]VO2+ [1] BlueV3+ [1] Green

V2+ Violet [1]

[4]

(c) (i) dissolve in water and add (excess) potassium hydroxide [1] a green-blue precipitate will form and then dissolve to give a deep green solution [1] add excess hydrogen peroxide and heat [1] the (green) solution turns yellow [1] boil the solution (and reduce the volume) [1] add named acid [1] orange solution/orange crystals [1] maximum [6] [6]


(ii) moles of chromium(III) chloride hexahydrate = 0.05 [1] theoretical yield of potassium dichromate = 0.025 mole [1] actual yield = 0.00997 mole [1] % yield = 40% [1] [4] 22









[Turn over

17 (a)

C

H

N

O

( CH2)4 ( CH2)6 ( CH2)4 ( CH2)6C

O H

N C

O H

NC

O H

N Each error [–1] [3]

(b) (i) HOCH2CH2OH [1]

(ii) ethane-1,2-diol [1]

(c) (i) 2 [1]

(ii)

NH2HO

O

C C

O

OH H2N [2]

(d) 3-methylpent-2-ene [2] 10

Section B 100

Total 120



TIME

2 hours.


Write your Centre Number and Candidate Number in the spaces provided at the top of this page.Answer all fourteen questions.Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering.Answer all four questions in Section B. Write your answers in the spaces provided in this question paper.


The total mark for this paper is 120.Quality of written communication will be assessed in question 13(e)(iii).

In Section A all questions carry equal marks, i.e. two marks for each question.In Section B the figures printed down the right-hand side of pages indicate the marks awarded to each question or part question.A Periodic Table of the Elements, containing some data, is included in this question paper.


2013

8214.02R

Chemistry



[AC222]


Centre Number

71

Candidate Number

AC

222

For Examiner’suse only

Question Number Marks

Section A

1–10

Section B

11

12

13

14

TotalMarks

1106

05

8214.02R 2

Section A



1 The standard electrode potentials for some half-cells are listed below:

Cu21(aq) 1 2e2 Cu(s) 10.34 V

AgCl(s) 1 e2 Ag(s) 1 Cl2(aq) 10.22 V

H1(aq) 1 e2 1–2 H2(g) 0.00 V

Zn21(aq) 1 2e2 Zn(s) 20.76 V

Which one of the following cell potentials could be obtained by combining two of these standard electrodes?

A 0.42 V

B 0.54 V

C 0.56 V

D 0.98 V

2 In which one of the following reactions is the inorganic reagent acting as an electrophile?

A CH3CH3 1 Cl2 CH3CH2Cl 1 HCl

B CH4 1 4Cl2 CCl4 1 4HCl

C 1 Br2 Br 1 HBr

D CH3 1 Br2 CH2Br 1 HBr

3 Which one of the following is the total number of isomers, both structural and stereoisomers, which are possible for the formula C4H10O?

A 3 or less

B 4

C 5

D 6 or more

8214.02R 3 [Turn over

4 Which one of the following is the name of the indicator used for the titration of magnesium ions with edta?

A Eriochrome

B Eriochrome T

C Eriochrome brown T

D Eriochrome black T

5 The structure of the polymer perspex is shown below.

C C C C C C

H H H

H H H CO2CH3 CO2CH3 CO2CH3

CH3 CH3 CH3

Which one of the following structures is that of the monomer from which perspex is formed?

CH3

CO2CH3

H

H

A

C C

H

CO2CH3

CH3

H

B

C C

CH3

CO2CH3

H

CH3

C

C C

H

CO2CH3

H

H

D

C C

6 Which one of the following statements describes the primary structure of a protein?

A The formation of the a-helix

B The folding of the a-helix

C The sequence of the amino acids in the chain

D The sequence of peptide links in the chain

8214.02R 4

7 Which one of the following graphs represents the absorbance against volume in a colorimetry experiment for the reaction of copper(II) nitrate with ammonia?

0.05 M (Cu(NO3)2(aq)0.10 M NH3(aq)

absorbance

010

55

10 0

volume (cm3)

A

absorbance

010

6.63.3

10 0

volume (cm3)

0.10 M (Cu(NO3)2(aq)0.05 M NH3(aq)

B

0.05 M (Cu(NO3)2(aq)0.10 M NH3(aq)

absorbance

010

3.36.6

100

volume (cm3)

C

0.10 M (Cu(NO3)2(aq)0.05 M NH3(aq)

absorbance

010

55

100

volume (cm3)

D


8 Which one of the following compounds is the least soluble in water at room temperature?

A CH3CH(NH2)CO2H

B CH3CH2CH2 NH2

C C6H5CO2Na

D C6H5NH2

9 In which one of the following reactions is the transition metal, transition metal compound or ion not acting as a catalyst?

A Iron in the production of ammonia

B Nickel in the formation of ethane from ethene

C Silver ions in the oxidation of ethanal

D Vanadium pentoxide in the manufacture of sulfuric acid

10 Complete combustion of 0.70 dm3 of a gaseous organic compound at 20 oC and one atmosphere pressure gave 0.12 mole of carbon dioxide.

Which one of the following is the number of carbon atoms in one molecule of the compound?

A 1

B 2

C 4

D 6

8214.02R 6

Examiner Only

Marks Remark

Section B

Answer all four questions in the spaces provided.

11 Benzedrine is the trade name for a mixture of the optical isomers of amphetamine. It was used as a stimulant in World War II and continues to be used in this way today.

(a) Benzedrine may be synthesised by the route shown below.

1 2 3 4 CH2CH2CH3 CH5CHCH3 CH2CHBrCH3 CH2CHNH2CH3

benzedrine

(i) In step 1 a reaction occurs which has a very similar mechanism to that of the monobromination of benzene. With bromination the electrophile is Br1, in this case the electrophile is CH3CH2CH2

1. Draw a flow scheme for this reaction.

[3]

(ii) In step 2 the propylbenzene is broken down into smaller molecules (cracked) in the presence of zinc oxide. Suggest the role of the zinc oxide and the conditions under which the cracking is carried out.

[3]

Examiner Only

Marks Remark


(iii) In step 3 name the reagent which adds across the double bond.

[1]

(iv) In step 4 name the reagent which is used to replace the bromine atom in the compound.

[1]

(b) (i) Deduce and explain whether benzedrine is a primary, secondary or tertiary amine.

[2]

(ii) Explain its strength as a base compared with phenylamine.

[2]

(c) Benzedrine forms salts with inorganic acids. The sulfate salt is often used as the main form of benzedrine in medicine.

(i) Write the equation for the formation of the sulfate salt of benzedrine.

[2]

(ii) Suggest why the formation of an ionic salt is more beneficial if tablets of the drug are used.

[1]

(iii) The amine can be liberated from the salt. Name the reagent and the conditions used for this reaction.

[2]

Examiner Only

Marks Remark

8214.02R 8

(d) Benzedrine is optically active and exists in two forms one of which is more biologically active than the other. This variation in activity is explained in a similar way to that of enzyme activity.

(i) Explain why benzedrine is optically active.

[1]

(ii) Explain why one structure is more biologically active than the other.

[1]

(e) The identification of many drugs uses the technique of GLC. Explain how this is carried out.

[2]

Examiner Only

Marks Remark

8214.02R 10

12 Iron is a transition element that forms a wide variety of complexes and salts. For example, with ethanedioic acid (oxalic acid) iron can form salts such as iron(II) oxalate and iron(III) oxalate. It can also form complexes such as potassium iron(III) oxalate.

COOH COOH

oxalic acid

(a) (i) Write the formulae of iron(II) oxalate and iron(III) oxalate.

iron(II) oxalate [1]

iron(III) oxalate [1]

(ii) The oxalate ion is colourless. What are the expected colours of the aqueous oxalate solutions listed below?

aqueous iron(II) oxalate [1]

aqueous iron(III) oxalate [1]

(iii) State and explain what would be observed when a solution of sodium hydroxide is added to each of the solutions.

[4]

(b) Iron(II) oxalate, when heated, decomposes to produce iron(II) oxide and both oxides of carbon. Write the equation for the reaction.

[1]

Examiner Only

Marks Remark


(c) Iron(II) oxalate is completely oxidised by acidified potassium manganate(VII). The iron(II) ion is oxidised to iron(III):

Fe21 Fe31 1 e2

The oxalate ion is completely oxidised to carbon dioxide.

COO2

2CO2 1 2e2

COO2

The electrons produced react with the manganate(VII) ion.

MnO42 1 8H1 1 5e2 Mn21 1 4H2O

(i) Write the equation for the reaction of acidified manganate(VII) ions with iron(II) oxalate.

[2]

(ii) Oxalic acid is used to remove iron stains because iron dissolves to form iron(II) oxalate. Calculate the mass of iron, in milligrams, dissolved in a 100 cm3 solution if 20.0 cm3 of the iron(II) oxalate solution reacts with 18.2 cm3 of 0.002 M potassium manganate(VII) solution.

[4]

Examiner Only

Marks Remark

8214.02R 12

(d) The oxalate ion also acts as a bidentate ligand. For example, iron(III) ions form the complex K3Fe(C2O4)3. The structure of the trisoxalato anion is based on an octahedron.

(i) Explain the meaning of the term complex.

[2]

(ii) Explain the meaning of the term bidentate ligand.

[2]

(iii) Suggest a 3D structure for the trisoxalato anion.

[2]

(iv) Explain why the trisoxalato anion is optically active.

[2]

(e) If a solution of K3Fe(C2O4)3 is treated with edta a reaction takes place. Suggest what reaction takes place and explain why it occurs.

[2]

Examiner Only

Marks Remark

8214.02R 14

13 Propanamide is a white crystalline solid with a melting point of 80 oC. It is prepared by heating the ammonium salt of propanoic acid.

(a) (i) Write the equation for the reaction of propanoic acid with ammonia.

[1]

(ii) Write the equation for the decomposition of this ammonium salt to produce propanamide.

[1]

(b) The nmr spectrum of propanamide is shown below.

� (ppm)

6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

(i) The signal at 0 ppm is due to TMS. Explain why TMS is used as a standard.

[2]

(ii) Explain why the signal at 1.15 ppm is a triplet.

[1]

(iii) Explain why the signal at 2.25 ppm is a quartet.

[1]

Examiner Only

Marks Remark


(iv) Explain why the signal at 5.5 ppm is at the highest chemical shift in the spectrum.

[1]

(v) Explain three ways in which this spectrum would differ from the spectrum of the N-methylated compound, CH3CH2CONHCH3.

[3]

(c) The mass spectrum of propanamide is shown below.

20 30 40 50 60 70 80

100

80

60

40

20

0

m/e

% a

bund

ance

(i) Write the formulae of the fragment ions which have the following masses.

29 [1]

44 [1]

(ii) Explain what is meant by the term fragmentation.

[2]

(iii) Identify the base peak in the spectrum.

[1]

Examiner Only

Marks Remark

8214.02R 16

(d) The amide group is hydrolysed slowly with water, rapidly by acids and far more rapidly by alkalis.

(i) Write the equation for the reaction of propanamide with aqueous sodium hydroxide.

[2]

(ii) The relative reactivity may be explained by the reactive species present in the three reactions. Suggest why the hydroxide ion is a better reagent than the hydrogen ion to attack the amide group.

[1]

(e) Polyamides such as nylon are important industrial chemicals.

(i) Write an equation to show the formation of a section of the nylon molecule using the industrial monomers.

[3]

(ii) State two major uses of nylon.

[2]

Examiner Only

Marks Remark


(iii) Nylon is far more easily disposed of than polythene. Explain using the chemical structure of nylon why this is so and state how waste polythene is disposed of apart from recycling.

[4]


Examiner Only

Marks Remark

8214.02R 18

14 Benzene, C6H6, was first isolated by Faraday in 1825. It is a colourless liquid with a melting point of 6 oC and a boiling point of 80 oC.

It is either represented by the Kekulé structure or by the more modern structure of a circle inside the ring.

Kekulé structure modern structure

(a) What is the empirical formula of benzene?

[1]

(b) What is the shape of benzene?

[1]

(c) Benzene may be catalytically reduced in several steps to cyclohexane using nickel.

(i) Write the overall equation for the reduction.

[1]

(ii) Draw a flow scheme showing the structure of all the reduction products.

[2]

(iii) Explain, in terms of chemisorption, the role of nickel in the reduction.

[3]

Examiner Only

Marks Remark


(d) The enthalpy of hydrogenation of cyclohexene is 2120 kJ mol21.

(i) What does this suggest for the value for the hydrogenation of benzene?

[1]

(ii) The actual hydrogenation value for benzene is 2208 kJ mol21. Suggest the reason for the difference.

[1]

(e) Draw a dot and cross diagram for the Kekulé structure of a benzene molecule using outer electrons only.

[3]

(f) Compare the reaction of bromine with benzene and ethene by drawing the following flow schemes:

(i) Draw a flow scheme to show the mechanism for the reaction of bromine with benzene.

[3]

(ii) Draw a flow scheme to show the mechanism for the reaction of bromine with ethene where Br1 is the electrophile.

[3]

Examiner Only

Marks Remark

8214.02R 20

(iii) Explain why there are different mechanisms for the reactions.

[2]

(g) Benzene is colourless but the solid pentacene is red.

pentacene

Explain why pentacene is coloured and benzene is not.

[4]

THIS IS THE END OF THE QUESTION PAPER


2013




[AC222]


8214.01 F

MARKSCHEME

8214.01 F 3

AVAILABLEMARKS

Section A

1 D

2 C

3 D

4 D

5 A

6 C

7 C

8 D

9 C

10 C


Section A 20

8214.01 F 4 [Turn over

AVAILABLEMARKS

Section B

11 (a) (i)

CH3CH2CH2

H+

CH3CH2CH2

+ H+

CH3CH2CH2 +

+

[3]

(ii) Zinc oxide is a catalyst [1] Conditions are high temperature [1] and pressure [1] [3] or finely divided catalyst or lack of air/oxygen

(iii) Hydrogen bromide [1]

(iv) Ammonia [1]

(b) (i) Primary amine [1] NH2 is attached to one carbon atom [1] [2] (ii) It is stronger [1] because the lone pair on nitrogen is more readily available (compared to phenylamine) [1] [2]

(c) (i) CH2CHNH2CH3

2 + H2SO4 SO4

CH2CHNH3CH3 +

2

2 _

[2]

(ii) Ionic salt is (more) soluble (than benzedrine) [1] or ionic salt is solid

(iii) Potassium/sodium hydroxide [1] Aqueous/heat [1] [2]

(d) (i) Four different atoms/groups attached to a carbon atom [1]

(ii) One structure fits into the “enzyme” better than the other i.e. by a lock and key mechanism [1]

(e) (Drugs injected into GLC equipment and) pass through at different speeds/retention times [1] Each drug produces a distinct peak/retention time [1] [2] 21

8214.01 F 5

AVAILABLEMARKS

12 (a) (i) iron(II) oxalate Fe

or Fe(COO)2 or FeC2O4 [1]

iron(III) oxalate Fe2

or Fe2(C2O4)3 [1]

3

(ii) iron(II) oxalate green [1]

iron(III) oxalate yellow/orange [1]

(iii) Green [1] precipitate [1] (of iron(II) hydroxide) [2] Rust/brown [1] precipitate [1] (of iron(III) hydroxide) [2] [4]

(b) Fe

→ FeO + CO + CO2 [1]

(c) (i) 3MnO4– + 24H+ + 5Fe(COO)2 → 3Mn2+ + 12H2O + 5Fe3+ + 10CO2 [2]

(ii) 18.2 cm3 of 0.002 M potassium manganate(VII) solution contains

18.2 × 10–3 × 0.002 mole of MnO4– = 0.0364 × 10–3 mol

= 3.64 × 10–5 mol 3MnO4

– = 5Fe(COO)2 = 5Fe hence moles of Fe in 20 cm3 = 53 × 3.64 × 10–5 mol

= 6.067 × 10–5 mol

hence grams of Fe in 20 cm3 = 56 × 6.067 × 10–5 mol

= 3.397 × 10–3 g

in 100 cm3 of solution = 5 × 3.397 × 10–3 = 0.017 g

= 17 (mg) [4]

(d) (i) A central metal ion/atom, with ligands attached by coordinate bonds [2]

(ii) An ion or molecule ligand which uses two lone pairs of electrons to form two coordinate bonds with a central metal ion in a complex [2]

(iii) ox =

COO–

COO–Fe

ox

ox

ox

[2]

(iv) It is not superimposable on its mirror image/rotates the plane of plane polarised light [2]

(e) edta replaces the oxalate ions [1] there is an increase in entropy [1] [2] 25


AVAILABLEMARKS

13 (a) (i) CH3CH2COOH + NH3 → CH3CH2COONH4 [1]

(ii) CH3CH2COONH4 → CH3CH2CONH2 + H2O [1] (b) (i) It only produces one signal (for the methyl groups) [1] which is out of the region for most proton spectra [1] [2]

(ii) The proton is next to a methylene/CH2 group [1]

(iii) The proton is next to a methyl/CH3 group [1]

(iv) The protons are next to nitrogen which is deshielding/ withdraws electrons [1]

(v) An extra peak [1] which would be below the quartet [1] The integration would show 3:2:1:3 [1] Some/all the peaks would change their chemical shift [1] To a maximum of [3] [3]

(c) (i) 29 C2H5+ [1]

44 CONH2+ [1]

(ii) (A positively charged ion produced when) the molecular ion [1] breaks apart [1] [2]

(iii) Base peak = 44 [1]

(d) (i) CH3CH2CONH2 + NaOH → CH3CH2COONa + NH3 [2] (ii) The hydroxide ion is attracted to the δ+ of the carbonyl group [1]

(e) (i) HOOC(CH2)4COOH + NH2(CH2)6NH2 → –OC(CH2)4CONH(CH2)6NH– + H2O [3] (ii) e.g. ropes/brushes/clothes [2]

(iii) Nylon is a polyamide/amide hence can be hydrolysed (to form the original molecules) Polythene cannot be hydrolysed (as it contains carbon–carbon bonds) hence it is either dumped or burned To a maximum of [4] [4]


8214.01 F 7

AVAILABLEMARKS14 (a) CH [1]

(b) (Hexagonal and) planar/flat [1]

(c) (i) C6H6 + 3H2 → C6H12 [1]

(ii) No need for the presence of hydrogen

[2]

(iii) Adsorption on the surface/formation of bonds [1] Orientation of molecules/d-orbitals involved [1] Bonds weakened within reactants/bonds formed in products [1] [3]

(d) (i) –360 kJ [1]

(ii) Benzene is more stable/the bonds are delocalised/the bonds are not real double bonds [1]

(e)

C ××××C

CC

C

C

×

×H××

×H××××

H

××

×××× ××

×H

×H

×H

[3] (f) (i)

Br+ + H+

BrH Br

+

[3]

(ii) CH2 CH2 + Br+ → +CH2 CH2Br → CH2Br CH2Br

[3]

(iii) The double bonds in the benzene molecules are stable/ delocalised [1] electrons in the ethene double bond are more readily available [1] [2] (g) Pentacene has an extensively delocalised electron system [1] The energy levels are close together [1] Less energy is needed to raise the electrons to a higher level [1] Energy is thus in the visible region [1] Colours other than red are absorbed (by pentacene) [1] To a maximum of [4] [4] 25

Section B 100

Total 120

Br–

or

TIME2 hours.

INSTRUCTIONS TO CANDIDATESWrite your Centre Number and Candidate Number in the spaces provided at the top of this page.Answer all seventeen questions.Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering.Answer all seven questions in Section B. Write your answers in the spaces provided in this question paper.

INFORMATION FOR CANDIDATESThe total mark for this paper is 120.Quality of written communication will be assessed in Question 17(g).In Section A all questions carry equal marks, i.e. two marks for each question.In Section B the figures printed down the right-hand side of pages indicate the marks awarded to each question or part question.A Periodic Table of the Elements, containing some data, is included in this question paper.

9342



Section A1–10

Section B11121314151617

TotalMarks

Centre Number

Candidate Number

Chemistry





2015

*ac222*

AC

222

9342 2

Section A



1 The chromatogram below was produced by two-way paper chromatography of a mixture of amino acids.

X

W

Z

Y

Solvent front 2

Solvent front 1

The table below gives the Rf values of some amino acids.

Amino acidRf values

Solvent 1 Solvent 2

Alanine 0.51 0.38

Asparagine 0.63 0.21

Isoleucine 0.44 0.72

Glycine 0.12 0.26

Lysine 0.18 0.14

Which one of the spots, W, X, Y or Z is glycine?

A W

B X

C Y

D Z

9342 3 [Turn over

2 Standard electrode potentials for two half-cells are shown below:

half-cell standard electrode potential/V

Ce31(aq) 1 3e2 ? Ce(s) 22.3

Th41(aq) 1 4e2 ? Th(s) 21.9

Which one of the following species is the most powerful reducing agent?

A Ce31(aq)

B Ce(s)

C Th41(aq)

D Th(s)

3 Which one of the following is not true for gas-liquid chromatography of a mixture?

A The liquid phase is mobile and the gas phase is stationary

B The molecules in the mixture have characteristic retention times

C The mixture is separated by partition between the liquid and the gas phase

D The percentage composition of the mixture can be determined

4 Which one of the following is the structure of terephthalic acid?

COOHCOOH

COOH

COOH

A B

COOH

HOOC

COOH

COOH

C D

9342 4

5 When carrying out an edta titration to find the concentration of calcium ions in a solution the solution is buffered to

A pH 4 and the colour change at the end point is blue to red.

B pH 4 and the colour change at the end point is red to blue.

C pH 10 and the colour change at the end point is blue to red.

D pH 10 and the colour change at the end point is red to blue.

6 Which one of the following is the weakest base?

A CH3CONH2

B C2H5NH2

C C6H5NH2

D NH3

7 The concentration of which one of the following solutions could be determined using colorimetry?

A Al31(aq)

B Ca21(aq)

C Fe31(aq)

D Zn21(aq)

8 Which one of the following is not true for glycine?

A It forms a blue solution with Cu2+(aq) ions

B It is optically active

C It reacts with sodium carbonate forming carbon dioxide

D It reacts with nitrous acid forming nitrogen

9342 5 [Turn over

9 How many p orbitals are involved in the delocalised π electrons of a benzene molecule?

A 2

B 3

C 6

D 12

10 Which one of the following is produced when CH3CONHCH3 is refluxed with excess dilute hydrochloric acid?

A CH3COOH and CH3NH2

B CH3COO2 and CH3NH31

C CH3COOH and CH3NH31

D CH3COO2 and CH3NH2

Examiner OnlyMarks Remark

9342 6

Section B


11 Vanadium is a typical transition metal.

(a) Explain, in terms of electronic configuration, what is meant by a transition metal.

[1]

(b) Vanadium has a variety of oxidation states.

(i) What is the electronic configuration of the V21 ion?

[1]

(ii) Complete the table below giving the formula, oxidation number and colour in solution of some vanadium ions.

ion oxidation number colour

V21 (aq)

yellow

VO21 (aq)

V31 (aq)

[4]


9342 7 [Turn over

(c) Vanadium(V) oxide is used as a catalyst in the manufacture of sulfuric acid.

(i) Vanadium(V) oxide is a heterogeneous catalyst. Explain why it is described as heterogeneous.

[1]

(ii) Explain, in terms of chemisorption, how vanadium(V) oxide acts as a catalyst.

[3]

(iii) The vanadium(V) oxide converts sulfur dioxide to sulfur trioxide forming vanadium(IV) oxide, which then reacts with oxygen to re-form the vanadium(V) oxide. Write equations for these two reactions.

[2]

(iv) Complete the table below by naming the catalyst used for each industrial process.

industrial process catalyst

formation of ammonia

oxidation of ammonia

[2]


9342 8

12 Phenylamine is involved in the manufacture of azo-compounds which can be used as dyestuffs.

(a) Phenylamine can be prepared from nitrobenzene according to the following flow scheme:

NH3Cl NH2NO2

A B

Name the reagents for steps A and B.

Step A [1]

Step B [1]

(b) Phenylamine is then converted to benzenediazonium chloride. Name the reagents and state the condition required to convert phenylamine to benzenediazonium chloride.

[2]

(c) Benzenediazonium chloride forms a yellow dye when coupled with dimethylaminobenzene.

N(CH3)2

dimethylaminobenzene

Write the equation for the reaction and circle the azo group.

[3]


9342 9 [Turn over

(d) Quinine is fluorescent, it absorbs ultraviolet light and then emits it as visible light.

OCH3

N

OH

N

quinine

(i) How does the frequency of visible light differ from the frequency of ultraviolet light?

[1]

(ii) Quinine is optically active. Circle the carbon asymmetric centres on the above diagram.

[2]


9342 10

13 (a) Benzene is more resistant than alkenes to reaction with bromine.

(i) What type of reaction do alkenes undergo with bromine?

[1]

(ii) Name a catalyst required for the reaction of benzene with bromine.

[1]

(iii) Draw a flow scheme to show the mechanism for the catalysed reaction of benzene with bromine.

[3]

(iv) Name the mechanism for the reaction of benzene with bromine.

[1]

(b) Toluene, C6H5CH3, can be nitrated in a similar way to benzene to form 2,4,6-trinitrotoluene.

(i) Suggest the structure of 2,4,6-trinitrotoluene.

[1]

(ii) Name the reagents used and write the equation for the formation of the nitronium ion.

Reagents:

Equation: [2]


9342 11 [Turn over

14 Polyurethane products have a wide variety of uses including insoles in shoes and structural foams. Polyurethane is made in a two-step process.

(a) Step 1: Ethane-1,2-diol and hexanedioic acid are polymerised to form a polyester.

(i) What type of polymers are polyesters?

[1]

(ii) Draw a diagram of one repeating unit of the polyester.

[2]

(b) Step 2: The polyester is then reacted with a di-isocyanate forming an amide linkage.

CH3

NCO

NCO

di-isocyanate

Draw a diagram for the isocyanate group, –NCO, showing all the bonds present.

[1]

(c) Polyurethane foams are readily combustible and are a fire hazard producing carbon monoxide when burnt. Explain why carbon monoxide is poisonous.

[2]

(d) Explain why polyurethanes are biodegradable.

[1]


9342 12

15 Putrescine is a foul smelling liquid produced by the breakdown of amino acids in dead organisms.

H2N(CH2)4NH2

putrescine

(a) (i) Suggest the systematic name for putrescine.

[1]

(ii) State why putrescine is soluble in water.

[1]

(b) Putrescine reacts in a similar way to ethylamine.

(i) Write an equation for the reaction of putrescine with excess nitrous acid.

[2]

(ii) Write an equation for the reaction of putrescine with excess ethanoyl chloride

[2]

(iii) Explain how the purified product formed between putrescine and excess ethanoyl chloride could be used to identify putrescine.

[2]

(c) Valine, CH3CH(CH3)CH(NH2)COOH, is an amino acid.

(i) Amino acids form zwitterions. What is a zwitterion?

[2]

(ii) Draw the zwitterion formed by valine.

[1]


9342 13 [Turn over

(iii) Valine is optically active. Draw the 3D representations of the optical isomers.

[2]

(d) Amino acids combine to form proteins. Describe the structure of proteins under the following headings.

Primary:

Secondary:

Tertiary:

[3]

(e) Some enzymes formed by proteins are used in biological washing powders.

(i) Describe how enzymes act as catalysts.

[2]

(ii) Explain why biological washing powders do not work at high temperatures.

[2]


9342 14

16 Nuclear magnetic resonance spectroscopy (nmr) is used to help understand the structure of molecules.

(a) TMS is the standard used in nmr.

(i) What is the chemical name for TMS?

[1]

(ii) Give two reasons why TMS is suitable for use as a standard in nmr.

[2]

(b) Sketch the nmr spectrum for methyl propanoate, CH3CH2COOCH3 showing the integration curve together with the splitting patterns. Indicate which hydrogen atoms are responsible for each peak.

TMS

[5]


9342 15 [Turn over

(c) The mass spectrum for methyl propanoate is shown below.

100

80

60

40

20

0.00.0 20 40 60 80 100

rela

tive

inte

nsity

m/z

(i) What is the m/z value of the base peak?

[1]

(ii) Suggest the formulae of the species responsible for the peaks at 31 and 57.

31:

57: [2]

(iii) Explain why there is a peak at 89.

[1]


9342 16

17 Chromium is purified in a number of steps after it is extracted from its ore.

Step 1: The impure chromium is heated with sodium carbonate in the presence of air to form sodium chromate(VI), Na2CrO4.

Step 2: The sodium chromate(VI) is converted to sodium dichromate which is then heated with carbon to form sodium chromate(III), Na2Cr2O4, and carbon monoxide.

Step 3: The Na2Cr2O4 is hydrolysed to form chromium(III) oxide. This is then reduced to chromium by aluminium.

(a) Write equations for the following reactions.

(i) The formation of sodium chromate(VI) in Step 1.

[2]

(ii) The formation of Na2Cr2O4 from sodium dichromate in Step 2.

[1]

(iii) The reduction of the chromium(III) oxide in Step 3.

[1]

(b) What is the colour change when sodium chromate(VI) is converted to sodium dichromate?

From: to [2]

(c) The oxygen atoms in the dichromate ion are arranged tetrahedrally around both chromium atoms. Draw a diagram below to suggest the 3D arrangement of the atoms in the dichromate ion.

[2]


9342 17 [Turn over

(d) Acidified dichromate ions can be used to determine the concentration of iron(II) ions. The half-equations for the reaction are:

Cr2O722 1 14H1 1 6e2 → 2Cr31 1 7H2O

Fe21 → Fe31 1 e2

(i) Write a balanced ionic equation for the reaction between acidified dichromate and iron(II) ions.

[1]

(ii) Five iron tablets containing iron(II) sulfate, FeSO4, were dissolved in acid and the solution made up to 250 cm3 in a volumetric flask. 25.0 cm3 of this solution required 23.5 cm3 of 0.01 mol dm23 sodium dichromate solution for complete oxidation. Calculate the mass of iron(II) sulfate in an iron tablet.

[4]

(e) Chromium(III) ions form a range of complex ions with a variety of ligands.

(i) Explain what is meant by the term ligand.

[2]


9342 18

(ii) The E–Z isomers of the complex ion [Cr(NH3)4Cl2]1 are shown below.

CrCI

CI

NH3

H3N

NH3

NH3

1

CrCI

NH3

H3N

NH3

CIH3N

1

Isomer 1 Isomer 2

Suggest and explain which structure is that of the E isomer and which is that of the Z isomer.

[3]

(f) The hydrated chromium(III) ions, [Cr(H2O)6]31, readily react with edta42 ions in a ligand replacement reaction.

(i) What term is given to ligands such as edta?

[1]

(ii) Write an equation for the reaction taking place between hydrated chromium(III) ions and edta4– ions.

[1]

(iii) Explain, in terms of entropy, why the reaction takes place.

[2]

9342 19


(g) Chromium forms the double salt chrome alum. Describe, giving experimental details, how you would prepare crystals of chrome alum from potassium dichromate.

[4]




2015




[AC222]


9342.01 F

MARKSCHEME

9342.01 F 3

AVAILABLEMARKS

Section A

1 A

2 B

3 A

4 C

5 D

6 A

7 C

8 B

9 C

10 C


Section A 20


AVAILABLEMARKS

Section B

11 (a) An element which forms (at least one stable) ion with a partially filled d-subshell/An element which has an atom with a partially filled d-subshell [1]

(b) (i) 1s2 2s2 2p6 3s2 3p6 3d3 [1]

(ii) ion oxidation

number colour

+2 VioletVO2

+(aq) +5+4 Blue+3 Green

(error [–1]) [4] (c) (i) It is in a different (physical) state to the reactants [1]

(ii) Reactants adsorbed onto the surface [1] Reactant bonds weakened [1] Orientation of molecules [1] [3] (Do not accept comments on catalytic action)

(iii) SO2 + V2O5 → SO3 + V2O4 [1] 2V2O4 + O2 → 2V2O5 [1] [2]

Accept VO2 instead of V2O4

(iv) industrial process catalyst

ironplatinum + rhodium

[2] 14

9342.01 F 5

AVAILABLEMARKS

12 (a) Tin and concentrated hydrochloric acid [1] (Free amine produced by reaction with) NaOH/KOH solution [1] [2]

(b) (Dilute) hydrochloric acid and sodium nitrite [1] Below 10 °C [1] [2]

(c) N2Cl + N(CH3)2 → N N N(CH3)2 + HCI (Equation [2], azo group [1]) [3]

(d) (i) Frequency has decreased [1]

(ii) OCH3

N

OH

N

[2] 10 3/4 = [2] 2 = [1] 1 = [0]

13 (a) (i) Electrophilic addition [1]

(ii) Iron/iron(III) bromide catalyst [1] (iii) H

Br+[FeBr4]_

+

Br [FeBr4]

_Br

+ HBr + FeBr3

or

H Br2 + FeBr3 → Br+ [FeBr4]

_

+

Br Br

+ H+


(iv) Electrophilic substitution [1]

(b) (i) CH3

NO2

NO2

O2N

[1] (ii) Concentrated nitric acid Concentrated sulfuric acid 1 [1]

HNO3 + 2H2SO4 → NO2+

+ 2HSO4– + H3O+ [1] [2] 9

Br+


AVAILABLEMARKS

14 (a) (i) Condensation [1]

(ii)

O (CH2)2 O C (CH2)4

C

O

O


(b) N C O [1]

(c) Carbon monoxide forms a stable complex with haemoglobin [1] preventing it from carrying oxygen [1] [2]

(d) The amide group can be hydrolysed [1] 7

15 (a) (i) 1,4-diaminobutane or butane-1,4-diamine [1]

(ii) The amino group(s) can form hydrogen bonds with water [1]

(b) (i) H2N(CH2)4NH2 + 2HNO2 → HO(CH2)4OH + 2H2O + 2N2

(2 marks, [–1] for each mistake) [2]

(ii) H2N(CH2)4NH2 + 2CH3COCl → H3CCOHN(CH2)4NHOCCH3 + 2HCI

(2 marks, [–1] for each error) [2]

(iii) Find the melting point of the solid [1] Compare with data book/actual melting point [1] [2]

(c) (i) Molecule or ion which has a permanent positive and negative charge but which is neutral overall/ion which has permanent –NH3

+ and –CO2

– and is neutral overall [2]

(ii) CH3CH(CH3)CH(NH3+)COO– [1]

(iii)

C COOH

H

NH2CH3CH(CH3) (CH3)CHCH3

C

H

H2NHOOC

([–1] for each mistake) [2] (d) Primary: sequence of amino acids in the chain [1] Secondary: the twisting/coiling of the chain to form a -pleated sheet/ -helix by (intramolecular) hydrogen bonding [1] Tertiary: the bending/folding of the secondary structure to give a 3D shape held together by hydrogen bonding/disulfide bridges/ionic interactions [1] [3]

(e) (i) Enzymes have an active site [1] which provides a path of lower activation energy [1] [2]

(ii) Intramolecular forces are disrupted/broken [1] The enzymes will be denatured/structure disrupted by higher temperatures/the active site will no longer be effective [1] [2] 20

9342.01 F 7

AVAILABLEMARKS

16 (a) (i) Tetramethylsilane [1]

(ii) All the hydrogen atoms are equivalent [1] the signal is outside the usual range [1] TMS is inert/unreactive [1] to a maximum of [2] [2]

(b)

CH3O

CH2

CH3

3

2

3 TMS

Splitting of peaks [1] Each set of peaks [3] – correct heights, shift and label Integration curve above [1] [5]

(c) (i) 29 [1]

(ii) CH3O+ [1] CH3CH2CO+ [1] (penalise no charge once) [2]

(iii) The presence of a carbon-13 atom [1] 12


AVAILABLEMARKS

17 (a) (i) 2Cr + 2Na2CO3 + 3O2 → 2Na2CrO4 + 2CO2 [2]

(ii) Na2Cr2O7 + 3C → Na2Cr2O4 + 3CO [1]

(iii) Cr2O3 + 2AI → 2Cr + AI2O3 [1]

(b) Yellow [1] to orange [1] [2]

(c)

O O

Cr Cr

O

O

O OO


(d) (i) Cr2O72– + 14H+ + 6Fe2+ → 2Cr3+ + 7H2O + 6Fe3+ [1]

(ii) Moles of Cr2O72– in 25 cm3 = (0.01 × 23.5)/1000 = 2.35 × 10–4

Moles of Fe2+ in 25 cm3 = (2.35 × 10–4) × 6 = 1.41 × 10–3

Moles of Fe2+ in 250 cm3 = 1.41 × 10–2 = 0.0141 Mass of FeSO4 in 250 cm3 = 0.0141 × 152 = 2.143 Mass of FeSO4 in one tablet = 2.143/5 = 0.429 g ([–1] for each mistake; [–1] if no mass unit) [4]

(e) (i) An ion or molecule with a lone pair of electrons which forms a coordinate bond with a (central) metal atom/ion in a complex [2]

(ii) Cl has a higher priority than N i.e. atomic number Cl > N [1] Isomer 1 has Cl on opposite sides [1] Isomer 1 is E [1] [3]

(f) (i) Polydentate/chelate/hexadentate [1]

(ii) [Cr(H2O)6 ]3+ + edta4– → [Cr(edta)]– + 6H2O [1]

(iii) More molecules/species on the right hand side [1] increases the entropy/disorder [1] [2]

(g) Cool a solution of potassium dichromate (Slowly) add concentrated sulfuric acid Add ethanol (slowly)(with stirring) Keep the temperature below 60 °C Leave to crystallise (and filter off crystals) [4]


Section B 100

Total 120

TIME2 hours.

INSTRUCTIONS TO CANDIDATESWrite your Centre Number and Candidate Number in the spaces provided at the top of this page.Answer all seventeen questions.Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering.Answer all seven questions in Section B. Write your answers in the spaces provided in this question paper.

INFORMATION FOR CANDIDATESThe total mark for this paper is 120.Quality of written communication will be assessed in Question 17(g).In Section A all questions carry equal marks, i.e. two marks for each question.In Section B the figures printed down the right-hand side of pages indicate the marks awarded to each question or part question.A Periodic Table of the Elements, containing some data, is included in this question paper.

9342



Section A1–10

Section B11121314151617

TotalMarks

Centre Number

Candidate Number

Chemistry





2015

*ac222*

AC

222

9342 2

Section A



1 The chromatogram below was produced by two-way paper chromatography of a mixture of amino acids.

X

W

Z

Y

Solvent front 2

Solvent front 1

The table below gives the Rf values of some amino acids.

Amino acidRf values

Solvent 1 Solvent 2

Alanine 0.51 0.38

Asparagine 0.63 0.21

Isoleucine 0.44 0.72

Glycine 0.12 0.26

Lysine 0.18 0.14

Which one of the spots, W, X, Y or Z is glycine?

A W

B X

C Y

D Z

9342 3 [Turn over

2 Standard electrode potentials for two half-cells are shown below:

half-cell standard electrode potential/V

Ce31(aq) 1 3e2 ? Ce(s) 22.3

Th41(aq) 1 4e2 ? Th(s) 21.9

Which one of the following species is the most powerful reducing agent?

A Ce31(aq)

B Ce(s)

C Th41(aq)

D Th(s)

3 Which one of the following is not true for gas-liquid chromatography of a mixture?

A The liquid phase is mobile and the gas phase is stationary

B The molecules in the mixture have characteristic retention times

C The mixture is separated by partition between the liquid and the gas phase

D The percentage composition of the mixture can be determined

4 Which one of the following is the structure of terephthalic acid?

COOHCOOH

COOH

COOH

A B

COOH

HOOC

COOH

COOH

C D

9342 4

5 When carrying out an edta titration to find the concentration of calcium ions in a solution the solution is buffered to

A pH 4 and the colour change at the end point is blue to red.

B pH 4 and the colour change at the end point is red to blue.

C pH 10 and the colour change at the end point is blue to red.

D pH 10 and the colour change at the end point is red to blue.

6 Which one of the following is the weakest base?

A CH3CONH2

B C2H5NH2

C C6H5NH2

D NH3

7 The concentration of which one of the following solutions could be determined using colorimetry?

A Al31(aq)

B Ca21(aq)

C Fe31(aq)

D Zn21(aq)

8 Which one of the following is not true for glycine?

A It forms a blue solution with Cu2+(aq) ions

B It is optically active

C It reacts with sodium carbonate forming carbon dioxide

D It reacts with nitrous acid forming nitrogen

9342 5 [Turn over

9 How many p orbitals are involved in the delocalised π electrons of a benzene molecule?

A 2

B 3

C 6

D 12

10 Which one of the following is produced when CH3CONHCH3 is refluxed with excess dilute hydrochloric acid?

A CH3COOH and CH3NH2

B CH3COO2 and CH3NH31

C CH3COOH and CH3NH31

D CH3COO2 and CH3NH2


9342 6

Section B


11 Vanadium is a typical transition metal.

(a) Explain, in terms of electronic configuration, what is meant by a transition metal.

[1]

(b) Vanadium has a variety of oxidation states.

(i) What is the electronic configuration of the V21 ion?

[1]

(ii) Complete the table below giving the formula, oxidation number and colour in solution of some vanadium ions.

ion oxidation number colour

V21 (aq)

yellow

VO21 (aq)

V31 (aq)

[4]