2010 al chem essence final 2

8/7/2019 2010 AL CHEM ESSENCE FINAL 2

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2010-AL-CHEM 211

Hong Kong Examinations and Assessment Authority

All Rights Reserved 2010

Not to be taken away before theend of the examination session

2010-AL

CHEM

PAPER 2

HONG KONG EXAMINATIONS AND ASSESSMENT AUTHORITY

HONG KONG ADVANCED LEVEL EXAMINATION 2010

CHEMISTRY A-LEVEL PAPER 2

1.30 am 4.30 am (3 hours)

This paper must be answered in English

1. There are TWO sections in this paper, Section A and Section B.

2. Section A carries 60 marks and Section B carries 40 marks.

3. AnswerALL questions from both Sections A and B.

4. Answers to questions in Section A and B are to be written in the AL(C) and

AL(E) Answer Books respectively.

5. Some constants, characteristic infra-red absorption wavenumber ranges, standard

reduction potentials and a Periodic Table can be found on pages 12, 13 and 14 of

this question book.


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SECTION A

AnswerALL questions, using the AL(C) Answer Book.

1. (a) The following shows the data from a study of mass spectrometry on a compound X. Threebbbbbbbbbbbbbbchemical species and the respective mass to charge ratios are hidden from the data.

(I) Deduce the hidden chemical species and the respective mass to charge ratios.

(II) Sketch the original mass spectrum on your Answer Book.

(iii) (I) Deduce the molecular geometry ofX.

(II) Calculate the relative molecular mass ofX.

(III) The relative molecular mass of X in benzene doubles its expected value.

Explain.

(7 marks)

m/z chemical species

162 (127I35Cl)+

164 (127I37Cl)+

197 (127

I35

Cl2)+

199 (127

I35

Cl37

Cl)+

201 (127I37Cl2)+

232 (127

I35

Cl3)+

234 (127I35Cl237Cl)+

236 (127

I35

Cl37

Cl2)+

238 (127

I37

Cl3)+


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1. (b) Calcium carbide (CaC2) crystallizes in a lattice structure of the following unit cell.

(i) Determine the number of calcium ions and a carbide ((CC)2-

) ions in an unit cell and

hence calculate the volume of an unit cell.

(Given: the density of CaC2 = 2.22 g cm-3

)

(ii) Calcium carbide reacts with nitrogen to form calcium cyanamide(CaCN2) at high

temperature.

(I) Draw the electronic structure of calcium cyanamide.

(II) Write a chemical equation for the formation of calcium cyanamide.

(III) Calculate the percentage composition of nitrogen in calcium cyanamide andhence suggest ONE of its applications.

(iii) Assume calcium cyanamide crystallizes in a lattice structure identical to calcium carbide,

compare their expected melting points in terms of electrostatic interaction. Explain.

(8 marks)

(c) Hydrogen peroxide (H2O2) is a pale blue liquid which appears colourless in diluted form.

(i) Hydrogen peroxide is a stronger bleaching agent with a manganese based catalyst than

without, which is more obvious at high temperature.

Explain.

(ii) Hydrogen peroxide exhibits many properties in common with chlorine.

(I) Which of their use as a bleaching agent, hydrogen peroxide with a manganesebased catalyst or sodium chlorite, is more environmentally benign ?

Explain.

(II) In a process of paper manufacturing, chlorine is replaced by hydrogen peroxide

mixed with an iron based catalyst to remove lignin from wood pulp.

Give an advantage of such a practice.

(5 marks)

Go on to the next page


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2. (a) Bromide ion reacts with bromate(V) ion according to the equation shown below:

5Br-(aq) + BrO3

-(aq) + 6H

+(aq) 3Br2(aq) + 3H2O(aq)

(i) (I) Write the chemical equation for the reaction between bromine and phenol.

(II) Methyl orange can be bleached by bromine. Explain how the above progress ofreaction can be monitored by addition of phenol and methyl orange.

Hint: Hydroxyl group is an electron-donating substituent.

(ii) The experiment in an attempt to find the initial rate was carried out under differenttemperature. The following lists the results:

Experiment Temperature / oC Time for specific event to happen / s

1 30 1054

2 37 595

3 41 387

4 44 306

5 49 211

(I) Suppose the specific event indicates the absence of bromine in the reactionmixture. Derive an expression correlating the time for the specific event to

happen tand the activation energy Ea.

(II) Hence, or otherwise, determine the Ea by plotting a suitable graph.

(Given: Arrhenius equation: k= Ae-Ea/RT)

(8 marks)

(b) (i) State ONE characteristic of a dynamic equilibrium and ONE application, other than

ffffkkkkkkkkfffffsolvent extraction, of partition coefficient.

(ii) In an experiment to determine the structure of a copper complex, 5 M NH3(aq) was added

into 1 M CuSO4(aq) and was shaken to form the complex N. Afterwards, CCl4(l) was

added into the mixture in a separating funnel and the resulting mixture was shaken again.

25 cm3 of the organic layer was extracted and titrated against with HCl(aq). 9.63 cm3 of

0.1 M HCl(aq) was required to attain complete neutralisation.

(At 298 K, the partition coefficient of NH3 between CCl4(l) and H2O(l) is 0.04.)

(I) Determine the coordination number of copper in N.

(II) Deduce the structure ofN.

(5 marks)


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2010-AL-CHEM 255

2. (c) The major buffer system in maintaining a certain pH value of venous blood is shown below:

CO2 + H2O H+

+ HCO3-

Ka = 8.30 x 10-7

mol dm-3

(i) Explain how the system works as a buffer when OH-ions are introduced into the system.

(ii) Given that the ratio of [HCO3-] to [CO2] = 20 : 1 , calculate the approximate pH value ofnormal blood sample.

(iii) The quantity of CO2 + HCO3- content can be determined by the following procedures.

1. Heat 200 cm3 of blood sample with excess dilute sulphuric(VI) acid.

2. Absorb the carbon dioxide evolved using barium hydroxide.

3. Filter off the barium carbonate precipitate.

4. Dry the precipitate and weigh it.

Given that 0.8 g of barium carbonate was formed in a determination, write the chemical

equation for the reaction that occurred and calculate the total number of mole of CO 2 +

HCO3- in the blood sample used.

(iv) Using the above information, determine the approximate concentration CO2(aq) in a

normal blood sample.

(7 marks)



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3. (a) Lead-acid accumulator is a secondary cell commonly used as car batteries.

(i) Is a porous partition necessary for the above cell ? Explain.

(ii) The following table shows the reaction occuring at the electrodes of the cell.

(I) Calculate the voltage the cell can generate.

(II) State the positive electrode for the lead acid accumulator.

(III) Write the full chemical equation for the reaction that occurs.

Indicate the direction of equilibrium as charging and discharging properly.

(IV) Explain why it is not desirable to charge the accumulator too rapidly.

(V) Suggest a physical method to monitor the status of charge for the above cell.

Explain the principle behind.

(8 marks)

Reaction Potential / V

Anode Pb(s) + SO42-

(aq) PbSO4(s) + 2e-

+ 1.69

Cathode PbO2(s) + 4H+(aq) + SO4

2-(aq) + 2e- 2PbSO4(s) + 2H2O(l) + 0.36

V

Pb(s) and spongy

PbO2(s)

Pb(s) andspongy Pb(s)

H2SO4(aq)


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2010-AL-CHEM 288

SECTION B

AnswerALL questions, using the AL(E) Answer Book.

4. (a) The following shows the structure of three amines A, B and C.

(i) Arrange amines A, B and C in increasing order of basicity. Explain your ordering.

(ii) State the number of carbon atom(s) which exhibit one-third of s-orbital character in

amine B. Explain your answer.

(iii) Discuss the aromaticity of amines A, B and C.

(5 marks)

4. (b) Loratadine, a prescription drug indicated for the symptomatic relief of allergy has the following

structure:

(i) Loratadine is commonly known as a tricyclic anti-histamine.

(I) State the number of aromatic ring(s) in the above structure. Explain.

(II) Propose a mechanism for its pharmacological effects.

(ii) An equimolar of loratadine and 2-chloro-2-methylpropane are treated with ethanolicsilver nitrate solution respectively.

(I) Draw the structure of 2-chloro-2-methylpropane.

(II) Give the expected observation in each of the above cases.

(III) Explain, in terms of the bonding and structure, why they differ in behaviour

towards the hydrolysis.

(7 marks)

N

Cl

O O

N

N

HNH2 NH2

CBA


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4. (c) Epoxy resin can be obtained phenol and propene via the following route.

(i) Suggest reactant(s) and conditions for each ofSteps 1, 2 and 3.

(ii) Outline the mechanism for the reaction in Step 1.

(iii) Name the type of reaction for the formation of bisphenol A from phenol.

(iv) Draw a portion of epoxy resin and hence discuss the following properties with regards toits structure and bonding.

(I) biodegradability

(II) thermostability

(9 marks)

polymerization

Epoxy resin

CH2

OH

Cl

O

Cl

OStep 1

(CH3)2CO

OHCH3

CH3

OHHO

bisphenol A

Step 2 Step 3



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5. (a) Serotonin (5-hydroxytryptamine) is a monoamine neurotransmitter, which is commonly present in

fungi. Its structure is shown below:

.

(i) Draw the structure of major organic products formed when it is treated with

(I) sodium hydroxide solution.

(II) sodium hydrogencarbonate solution.

(ii) It is known that the Ka of its ammonium salt is 2.0 x 10-7 and the that of phenolichydroxyl group is 1.58x10 -10. Suggest how you would extract serotonin from a sampleof mushroom.

(5 marks)

(b) Outline a synthetic route with no more than five steps to accomplish the following transformations.For each step, give the reagent(s), conditions and the structure of organic product.

(i)

(ii)

(7 marks)

CH2OH CH2CONH2

CN

CN

HN

HO

NH2


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5. (c) Figure 5.1 and Figure 5.2 below show the infra-red spectrum and mass spectrum of compound K,

with a relative molecular mass of 58 and composition by mass: C : 62.1%; H : 10.3%; O : 27.6%.

Based on the information in the figure and the data provided, deduce the structure ofK.

(7 marks)

END OF PAPER

transmittance(%)

wavenumber / cm-

Figure 5.1 Infra-red spectrum ofK

relativeintensity(%)

m/z

Figure 5.2 Mass spectrum ofK


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Constants

Gas constant, R = 8.31 J K-1

mol-1

Avogadro constant, L = 6.02x1023 mol-1Plank constant, h = 6.63x10-34 J sSpeed of light in vacuum, c = 3.00x108 m s-1Ionic product of water at 298 K, Kw= 1.00x 10-14 mol-2 dm-6Specific heat capacity of water = 4.18 J g

-1K

-1

Characteristic Infra-red Absorption Wavenumber Ranges

(Stretching modes)

Bond Compoundtype Wavenumber range /cm-1

C=C Alkene 1610 to 1680

C=O Aldehydes, ketones, carboxylic acids and derivatives 1680 to 1800

CC Alkynes 2070 to 2250

CN Nitriles 2200 to 2280

OH Acids (hydrogen-bonded) 2500 to 3300

CH Alkanes, alkenes, arenes 2840 to 3095

OH Alcohols, phenols (hydrogen-bonded) 3230 to 3670

NH Amines 3350 to 3500


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2010 al chem essence final 2

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