harris federation year 13c spring chemistry internal ... · 02/02/2018 · english 3.1.12 acids and...

Harris Federation

Year 13C

Spring Chemistry Internal Assessment

Student Name ..........................................................

Time allowed for this test is 1 hour 15 minutes

Answer all the questions

Use a black pen

Maximum mark for this test is 72

Ensure that throughout your test, you: o use good

English o organise

information clearly

o use specialist vocabulary where appropriate

Inorganic and Physical Questions

Question Topic Mark

Marks available

1-3 MCQ mixed 3

4 3.1.8 Thermodynamics

15

5 3.1.9 Rate equations

5

6 3.1.11 Electrode potentials

11

7 3.2.4 Properties of Period 3

12

8 3.2.5 Transition metals

11

9 3.1.12 Acids and bases

15

TOTAL 72 Grade

Harris Federation

Q1.The following information concerns the equilibrium gas-phase synthesis of methanol.

CO(g) + 2H2(g) CH3OH(g)

At equilibrium, when the temperature is 68 °C, the total pressure is 1.70 MPa. The number of moles of CO, H2 and CH3OH present are 0.160, 0.320 and 0.180, respectively.

Thermodynamic data are given below.

Substance ΔH / kJ mol−1 S / J K-1 mol-1

CO(g) −110 198

H2(g) 0 131

CH3OH(g) −201 240

With pressures expressed in MPa units, the value of the equilibrium constant, Kp, under

these conditions is

A 1.37

B 1.66

C 2.82

D 4.80 (Total 1 mark)

Q2.Rate = k [A]2 [B]

Correct units for the rate constant in the rate equation above are

A mol dm−3 s−1

B mol−1 dm−3 s−1

C mol2 dm−6 s−1

D mol−2 dm6 s−1

(Total 1 mark)

Q3.Which one of the following statements is not correct?

A The first ionisation energy of iron is greater than its second ionisation energy.

B The magnitude of the lattice enthalpy of magnesium oxide is greater than that of barium oxide.

C The oxidation state of iron in [Fe(CN)6]3− is greater than the oxidation state of copper in [CuCl2]−

D The boiling point of C3H8 is lower than that of CH3CH2OH (Total 1 mark)

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Q4.(a) Define the term electron affinity for chlorine.

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(b) Complete this Born−Haber cycle for magnesium chloride by giving the missing species on the dotted lines. Include state symbols where appropriate.

The energy levels are not drawn to scale.

(6)

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(c) Table 1 contains some enthalpy data.

Table 1

Enthalpy change / kJ mol−1

Enthalpy of atomisation of magnesium +150

Enthalpy of atomisation of chlorine +121

First ionisation energy of magnesium +736

Second ionisation energy of magnesium +1450

Enthalpy of formation of magnesium chloride −642

Lattice enthalpy of formation of magnesium chloride −2493

Use your Born−Haber cycle from part (b) and data from Table 1 to calculate a value for the electron affinity of chlorine.

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........................................................................................................................ (3)

(d) Table 2 contains some more enthalpy data.

Table 2

Enthalpy change / kJ mol−1

Enthalpy of hydration of Mg2+ ions −1920

Enthalpy of hydration of Na+ ions −406

Enthalpy of hydration of Cl− ions −364

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(i) Explain why there is a difference between the hydration enthalpies of the magnesium and sodium ions.

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(ii) Use data from Table 1 and Table 2 to calculate a value for the enthalpy change when one mole of magnesium chloride dissolves in water.

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(Total 15 marks)

Q5.The initial rate of the reaction between gases D and E was measured in a series of experiments at a constant temperature. The results are shown in the table.

Expt Initial [D] / mol

dm–3

Initial [E] / mol dm–3

Initial rate / mol dm–3 s–1

1 1.25 × 10–2 5.81 × 10–1 1.16 × 10–2

2 1.88 × 10–2 8.73 × 10–1 3.92 × 10–2

3 1.88 × 10–2 1.75 1.57 × 10–1

(a) Deduce the order of reaction with respect to D and the order with respect to E.

Order with respect to D .......................................................................................

Order with respect to E .......................................................................................

Space for working ...............................................................................................

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............................................................................................................................. (2)

Harris Federation

(b) Suggest why initial rates of reaction are used to determine these orders rather than rates of reaction at other times during the experiments.

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(c) State how the initial rate is obtained from a graph of the concentration of the product against time.

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(Total 5 marks)

Q6.The table shows some standard electrode potential data.

Electrode half-reaction EΘ/V

Zn2+(aq) + 2e– → Zn(s) –0.76

Co2+(aq) + 2e– → Co(s) –0.28

½O2(g) + 2H+ (aq) + 2e– → H2O(l) +1.23

Au+(aq) + e– → Au(s) +1.68

Co3+(aq) + e– → Co2+(aq)/p> +1.82

(a) (i) Identify the weakest oxidising agent in the table.

................................................................................................................... (1)

(ii) Give the conditions under which the electrode potential of the Zn2+/Zn electrode is –0.76 V.

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................................................................................................................... (2)

Harris Federation

(b) Two half-cells, involving species in the table, are connected together to give a cell with an e.m.f. = +0.48 V.

Use data from the table to deduce the conventional representation of this cell. Write the half-equation for the reaction that occurs at the negative electrode.

Conventional representation ...............................................................................

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Half-equation ....................................................................................................... (3)

(c) Use data from the table to identify a cobalt species that can react with water.

Write an equation for the redox reaction that occurs and identify the oxidation product in the reaction.

Cobalt species .....................................................................................................

Equation ..............................................................................................................

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Oxidation product ................................................................................................ (3)

(d) Use data from the table to explain why gold jewellery is unreactive in moist air.

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(Total 11 marks)

Harris Federation

Q7.This question is about the elements in Period 3 from sodium to phosphorus (Na to P) and their oxides.

(a) Element X forms an oxide that has a low melting point. This oxide dissolves in water to form an acidic solution.

(i) Deduce the type of bonding in this oxide of X.

................................................................................................................... (1)

(ii) Identify element X.

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(iii) Write an equation for the reaction between this oxide of X and water.

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(b) Element Y reacts vigorously with water. An oxide of Y dissolves in water to form a solution with a pH of 14.

(i) Deduce the type of bonding in this oxide of Y.

................................................................................................................... (1)

(ii) Identify element Y.

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(iii) Write an equation for the reaction of element Y with water.

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(iv) Write an equation for the reaction of this oxide of Y with hydrochloric acid.

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(c) Element Z forms an amphoteric oxide that has a very high melting point.

(i) Deduce the type of bonding in this oxide of Z.

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(ii) Write the formula of this amphoteric oxide.

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(iii) State the meaning of the term amphoteric.

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(iv) Write two equations to show the amphoteric nature of the oxide of Z.

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(Total 12 marks)

Q8.(a) A co-ordinate bond is formed when a transition metal ion reacts with a ligand.

Explain how this co-ordinate bond is formed.

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(b) Describe what you would observe when dilute aqueous ammonia is added dropwise, to excess, to an aqueous solution containing copper(II) ions. Write equations for the reactions that occur.

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Harris Federation

(c) When the complex ion [Cu(NH3)4(H2O)2]2+ reacts with 1,2-diaminoethane, the ammonia molecules but not the water molecules are replaced.

Write an equation for this reaction.

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(d) Suggest why the enthalpy change for the reaction in part (c) is approximately zero.

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(e) Explain why the reaction in part (c) occurs despite having an enthalpy change that is approximately zero.

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(Total 11 marks)

Q9.Ethanedioic acid is a weak acid. Ethanedioic acid acts, initially, as a monoprotic acid.

Harris Federation

(a) Use the concept of electronegativity to justify why the acid strengths of ethanedioic acid and ethanoic acid are different.

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(b) A buffer solution is made by adding 6.00 × 10–2 mol of sodium hydroxide to a solution containing 1.00 × 10–1 mol of ethanedioic acid (H2C2O4). Assume that the sodium hydroxide reacts as shown in the following equation and that in this buffer solution, the ethanedioic acid behaves as a monoprotic acid.

H2C2O4(aq) + OH–(aq) HC2O4–(aq) + H2O(l)

The dissociation constant Ka for ethanedioic acid is 5.89 × 10–2 mol dm–3.

Calculate a value for the pH of the buffer solution. Give your answer to the appropriate number of significant figures.

pH = .................................... (5)

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(c) In a titration, the end point was reached when 25.0 cm3 of an acidified solution containing ethanedioic acid reacted with 20.20 cm3 of 2.00 ×10–2 mol dm–3 potassium manganate(VII) solution.

Deduce an equation for the reaction that occurs and use it to calculate the original concentration of the ethanedioic acid solution.

Equation .........................................................................................................

Calculation

Original concentration = ............................... mol dm-3

(4) (Total 15 marks)

END OF EXAM

Harris Federation

M1.B [1]

M2.D [1]

M3.A [1]

M4.(a) The enthalpy change / heat energy change / ΔH for the formation of one mole of (chloride) ions from (chlorine) atoms

Allow enthalpy change for Cl + e− → Cl−

Do not allow energy change

ionisation energy description is CE=0

Allow enthalpy change for the addition of 1 mol of electrons to Chlorine atoms

penalise Cl2 and chlorine molecules CE = 0

allow chlorine ions 1

Atoms and ions in the gaseous state

Or state symbols in equation

Cannot score M2 unless M1 scored

except allow M2 if energy change rather than enthalpy change

ignore standard conditions 1

(b) Mg2+(g) + 2e− + 2Cl(g) (1) (M5)

Harris Federation

Allow e for electrons (i.e. no charge)

State symbols essential

If no electrons allow M5 but not M3,M4

If incorrect 1 / 2 Cl2 used allow M3 and M4 for correct electrons (scores 2 / 6)

6

(c) −ΔHf(MgCl2) + ΔHa(Mg) + 1st IE(Mg) + 2nd IE(Mg) +2ΔHa(Cl)= −2EA(Cl) − LE(MgCl2)

Allow Enthalpy of Formation = sum of other enthalpy changes (incl lattice formation)

1

−2EA(Cl) = 642 + 150 + 736 + 1450 + 242 − 2493 = 727 1

EA(Cl) = −364 (kJ mol−1 )

Allow −363 to −364 Allow M1 and M2 for −727 Allow 1 (1 out of 3) for +364 or +363 but award 2 if due to arithmetic error after correct M2 Also allow 1 for −303 Units not essential but penalise incorrect units Look for a transcription error and mark as AE−1

1

(d) (i) Magnesium (ion) is smaller and more charged (than the sodium ion) OR magnesium (ion) has higher charge to size ratio / charge density

Do not allow wrong charge on ion if given

Do not allow similar size for M1

Do not allow mass / charge ratio 1

Harris Federation

(magnesium ion) attracts water more strongly .

Mark independently

Mention of intermolecular forces, (magnesium) atoms or atomic radius CE = 0

1

(ii) Enthalpy change = −LE(MgCl2) + Σ(ΔHhydions)

= 2493 + (−1920 + 2 × −364) 1

= −155 (kJ mol−1)

Units not essential but penalise incorrect units 1

[15]

M5.(a) Order wrt D = 1 OR first OR [D] OR [D]1

Ignore working 1

Order wrt E = 2 OR second OR [E]2

1

(b) (At time zero/start) the concentrations are known 1

(c) M1 (Calculate) gradient (of tangent/curve/graph)

Allow description of gradient calculation:

Change in conc / time 1

M2 at t=0 or at start of graph/curve

M2 scored only if M1 gained

Ignore the word initial 1

[5]

M6.(a) (i) Zn2+

Zn2+(aq)

Apply List 1

(ii) 298 K /25°C

Ignore pressure

Harris Federation

Ignore standard conditions

Ignore state symbols 1

(Solutions at) unit concentration / 1 mol dm-3 (of Zn2+)

Ignore references to S.H.E 1

(b) Identifying it is the Zn/Zn2+ and Co2+/Co half cells 1

Correct order with phase boundaries and salt bridge correct, no Pt

If this is correct it scores M1 and M2

Allow double dashed line for salt bridge

Extra phase boundaries loses M2


Zn → Zn2+ + 2e(-)

M3 independent

Allow –2e- on LHS 1

(c) Co3+

Mark independently 1

2Co3+(aq) + H2O(l) 2Co2+(aq)+ ½ O2(g) + 2H+(aq)

Ignore state symbols

Allow multiples 1

Oxygen /O2

Allow ½ O2

1

(d) EΘ (O2(|H2O)) electrode EΘ (Au+(|Au)) OR EΘ (Au+(|Au)) > EΘ (O2(|H2O)) OR the EΘ (Au+|Au) electrode potential is more positive than the EΘ (O2|H2O) electrode OR The emf (for the reaction of Au and oxygen) is –0.45 V (and therefore not spontaneous)

Mark independently 1

Harris Federation

So oxygen is unable to oxidise gold

Ignore references to water

Allow gold cannot reduce oxygen 1

[11]

M7.(a) (i) Covalent

Ignore simple / molecular

Do not allow macromolecular/giant covalent/dative/dipole- dipole/Hydrogen bonds

Ignore VdW 1

(ii) P / phosphorus / P4

1

(iii) P4O10 + 6H2O → 4H3PO4

Mark independently of (a)(ii)

Accept multiples/fractions


Allow ions on the RHS (→ 12H+ + 4PO43-)

Allow correct equations from P4O6, P2O3 and P2O5

P4O6 + 6H2O → 4H3PO3

P2O3 + 3H2O → 2H3PO3

P2O5 + 3H2O → 2H3PO4

1

(b) (i) Ionic

Ignore giant / lattice 1

(ii) Na / Sodium 1

(iii) 2Na + 2H2O → 2Na+ + 2OH- + H2

Allow equation to form 2NaOH



(iv) Na2O + 2HCl → 2NaCl + H2O



Allow ions, but do not allow H+ only for the acid

Harris Federation

1

(c) (i) Ionic

Allow ionic and covalent / ionic with covalent character 1

(ii) Al2O3


(iii) Reacts with acids and bases

Allow reacts with acids and alkalis / acts as both an acid and a base / shows acidic and basic properties

1

(iv) Al2O3 + 6HCl → 2Al3+ + 6Cl- + 3H2O

Al2O3 + 6H+ → 2Al3+ + 3H2O

Allow equation to form 2AlCl3 (but not Al2Cl6)

Allow equations with other acids 1

Al2O3 + 2NaOH + 3H2O → 2Na+ + 2[Al(OH)4]–

Al2O3 + 2OH– + 3H2O → 2[Al(OH)4]–

Al2O3 + 2NaOH + 7H2O → 2Na+ + 2[Al(OH)4 (H2O)2]–

Al2O3 + 2OH– + 7H2O → 2[Al(OH)4 (H2O)2]–

Allow equations to form 2Na[Al(OH)4] or 2Na[Al(OH)4(H2O)2]

Allow equations with other alkalis

Allow correct equations which form [Al(OH)6]3-

Allow equations to form [Al(OH)x(H2O)6-x]3-x etc


[12]

M8.(a) An electron pair on the ligand 1

Is donated from the ligand to the central metal ion 1

(b) Blue precipitate 1

Harris Federation

Dissolves to give a dark blue solution 1

[Cu(H2O)6]2+ + 2NH3 Cu(H2O)4(OH)2 + 2NH4+

1

Cu(H2O)4(OH)2 + 4NH3 [Cu(NH3)4(H2O)2]2+ + 2OH– + 2H2O 1

(c) [Cu(NH3)4(H2O)2]2+ + 2H2NCH2CH2NH2 [Cu(H2NCH2CH2NH2)2(H2O)2]2+ + 4NH3

1

(d) Cu–N bonds formed have similar enthalpy / energy to Cu–N bonds broken 1

And the same number of bonds broken and made 1

(e) 3 particles form 5 particles / disorder increases because more particles are formed / entropy change is positive

1

Therefore, the free-energy change is negative

M2 can only be awarded if M1 is correct 1

[11]

M9.(a) This question is marked using levels of response. Refer to the Mark Scheme Instructions for Examiners for guidance on how to mark this question.

All stages are covered and the explanation of each stage is generally correct and virtually complete.

Answer is communicated coherently and shows a logical progression from stage 1 and stage 2 to stage 3. Steps in stage 3 must be complete, ordered

Harris Federation

and include a comparison. Level 3

5 – 6 marks

All stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies OR two stages are covered and the explanations are generally correct and virtually complete.

Answer is mainly coherent and shows a progression from stage 1 and stage 2 to stage 3.

Level 2

3 – 4 marks

Two stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies, OR only one stage is covered but the explanation is generally correct and virtually complete.

Answer includes some isolated statements, but these are not presented in a logical order or show confused reasoning.

Level 1

1 – 2 marks

Insufficient correct Chemistry to warrant a mark. Level 0

0 marks

Indicative Chemistry content

Stage 1: difference in structure of the two acids • The acids are of the form RCOOH • but in ethanoic acid R = CH3

• whilst in ethanedioic acid R = COOH

Stage 2: the inductive effect • The unionised COOH group contains two very electronegative oxygen

atoms • therefore has a negative inductive (electron withdrawing)effect • The CH3 group has a positive inductive (electron pushing) effect

Stage 3: how the polarity of OH affects acid strength • The O–H bond in the ethanedioic acid is more polarised / H becomes

more δ+

• More dissociation into H+ ions • Ethanedioic acid is stronger than ethanoic acid

6

(b) Moles of NaOH = Moles of HOOCCOO– formed = 6.00 × 10–2

Extended response 1

Moles of HOOCCOOH remaining = 1.00 × 10–1 – 6.00 × 10–2

= 4.00 × 10–2

1

Harris Federation

Ka = [H+][A–] / [HA]

[H+] = Ka × [HA] / [A–] 1

[H+] = 5.89 × 10–2 × (4.00 × 10–2 / V) / (6.00 × 10–2 / V) = 3.927 × 10–2

1

pH = –log10(3.927 ×10–2) = 1.406 = 1.41

Answer must be given to this precision 1

(c) 5H2C2O4 + 6H+ + 2MnO4– 2Mn2+ + 10CO2 + 8H2O

OR 5C2O42– + 16H+ + 2MnO4

– 2Mn2+ + 10CO2 + 8H2O 1

Moles of KMnO4 = 20.2 × 2.00 × 10–2 / 1000 = 4.04 × 10–4

1

Moles of H2C2O4 = 5 / 2 × 4.04 × 10–4 = 1.01 × 10–3

1

Concentration = moles / volume (in dm3)

= 1.01 × 10–3 × 1000 / 25 = 4.04 × 10–2 (mol dm–3)

If 1:1 ratio or incorrect ratio used, M2 and M4 can be scored 1

[15]

Harris Federation

E4.Many students failed to score 2 marks in part (a) for the definition of electron affinity. Common mistakes were to refer to energy rather than enthalpy change, to omit one mole of atoms or ions and to refer to chlorine molecules rather than atoms. Part (b) was usually answered well but some state symbols and electrons were common omissions. Good students scored full marks for part (c) but a very common error amongst others was to use the value of 121 kJ mol⁻¹ for the atomisation of chlorine instead of doubling that value to allow for 2 mol of chlorine atoms. In part (d)(i) a common omission was a failure to mention that magnesium ions are smaller than those of sodium and a common error was

to suggest that the ions would be attracted to O²⁻ ions in water. Answers to part (d)(ii) were usually correct.

E5.Part (a) was answered well and two thirds of students scored both marks. By contrast, part (b) was a hard question with few correct answers. Many students spoke about the changing concentrations but few mentioned the importance of knowing the initial concentration. The first mark in part (c) for mentioning a gradient was often gained but the location of where to measure the gradient was only given by a third of students.

E6.The correct answer was given by the majority of the students in part (a)(i). Part (a)(ii) was well done although a few students could not state the correct units of concentration. In part (b) the two half-cells were generally identified but the cell was often reversed as was the equation given. In part (c) the correct cobalt species was generally identified as the oxidising agent but the equation was often not balanced and the oxidation product given as Co2+ or H+. Students found part (d) challenging. Very few gave E⊖ with the correct terminology; very often this was given the wrong way round e.g. E⊖ Au/Au+. Most students thought, incorrectly, that the reaction was between gold and water. The E⊖ − values should have indicated to them that a redox reaction between gold and water is not feasible.

E7.This question was generally high scoring especially by the more able students. The types of bonding were generally well known. Common errors included sulfur in part (a), magnesium in part (b) and silicon in part (c) and therefore the equations could not gain credit. The correct equation between aluminium oxide and sodium hydroxide (or other alkalis) was not common in part (c) whilst the equation between aluminium oxide and an acid was better known.

harris federation year 13c spring chemistry internal ... · 02/02/2018 · english 3.1.12 acids and...

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