ocr a level chemistry a multip(le choice question...

Multiple Choice Questions (MCQ) topic quiz

5.1 Rates, equilibrium and pH

Instructions and answers for teachersThese instructions cover the learner activity section which can be found on page 10. This Lesson Element supports OCR A Level Chemistry A.

When distributing the activity section to the learners either as a printed copy or as a Word file you will need to remove the teacher instructions section.

The Activity This Lesson Element is a teaching and learning resource containing 10 multiple choice questions (MCQs) on the theme of rates, equilibrium and pH. Some questions might require synoptic thinking, using knowledge and ideas from various topics across the full A Level content.

This resource can be used to test and consolidate understanding at the end of a topic or to revisit and refresh knowledge at a later point in the course.

Learning OutcomesThis lesson element relates to the specification learning outcomes 5.1.1(b), 5.1.1(c), 5.1.1(d), 5.1.1(i), 5.1.1(k), 5.1.2(b), 5.1.2(f), 5.1.3(a), 5.1.3(g), 5.1.3(l)

Introduction Multiple choice questions allow rapid coverage of a wide range of sub-topics.

Contrary to a widespread belief among students, multiple choice questions are not necessarily easy – they can be easy, moderate or difficult.

The questions are written so that the incorrect answers are plausible distractors based on common errors or misconceptions.

The questions in this quiz cover topics mainly from specification sections:


Version 1 1 © OCR 2016

Multiple Choice Questions (MCQ) topic quiz – answers

1. Ka for ethanoic acid is 1.7 × 10–5 mol dm–3 at 25 °C.

What is the pH of a 0.125 mol dm–3 solution of ethanoic acid at this temperature?

A 0.75 They have treated is as a strong acid and got the calculation wrong, using 10–0.125

B 0.90 They have treated it as a strong acid, using –log 0.125.

C 2.8 Correct answer: pH = –log

D 5.7 This is probably a guess, the calculation is –log(0.125 × 1.7 × 10–5)

Your answer


C

2. A student monitors the rate of a reaction and plots the concentration of one reactant against time. The shape of the concentration–time graph is shown below.

What can be determined about this reaction?

A The reaction is zero order with respect to this reactant.

The line would be straight, and the half-life would decrease

B The reaction is first order with respect to this reactant.

Correct answer: The graph shows a downward curve with a constant half-life.

C The reaction is second order with respect to this reactant.

The line would initially be steeper and half-life would increase

D The rate of reaction is constant.

They may have noticed a constant half-life, but confused this with constant rate. The gradient of the graph becomes less steep over time, indicating a changing rate.

Your answer


B

3. Carbon monoxide reacts with nitrogen dioxide:

CO(g) + NO2(g) CO2(g) + NO(g)

This reaction follows a two-step mechanism:

2NO2(g) NO3(g) + NO(g) Slow step

CO(g) + NO3(g) CO2(g) + NO2(g) Fast step

What is the correct rate equation for the reaction?

A rate = k[CO][NO3] They have based the rate equation on the fast step rather than the slow step.

B rate = k[NO2]2[CO][NO3] They have based the rate equation on the reactants of both the slow and the fast step, rather than just the slow step.

C rate = k[NO2]2 Correct answer: The reactants in the slow step are two molecules of NO2.

D rate = k[NO2]2[NO3][NO] They have based the rate equation on all the species in the slow step, rather than just the reactants.

Your answer

4. The Arrhenius equation k = Ae–Ea/RT can be rearranged so it can be represented by a straight-

line graph.

Which expression represents the gradient of the graph?

A –Ea/R Correct answer: note that the linear expression is given on the Data Sheet.

B ln A This would be the value of the y-intercept, used to determine A.

C ln k This is plotted on the y-axis.

D 1/T This is plotted on the x-axis.

Your answer


C

A

5. A student mixes 6.0 mol of ethanoic acid and 12.5 mol of ethanol and allows an equilibrium

to establish:

CH3COOH(l) + CH3CH2OH(l) CH3COOCH2CH3(l) + H2O(l)

At equilibrium 1 mol of ethanoic acid remains.

Which row gives the correct amounts of each substance at equilibrium?

Amount (in mol) of substance

CH3COOH C2H5OH CH3COOCH2CH3 H2O

A 1 7.5 1 1

They have not realised that the amount of product increases as reactants are used up.

B 1 7.5 5 5

Correct answer.

C 1 12.5 5 1

They have connected the ethanoic acid reacted to the ester formed, but not thought through what happens to the other species.

D 1 12.5 5 5

They have not subtracted the 5 mol from the ethanol.

Your answer


B

6. A mixture contains:

20 mol N2(g)

60 mol H2(g)

20 mol NH3(g)

The total pressure is 20 200 kPa.

What is the partial pressure of hydrogen?

A 336.7 kPa They have just divided 20 200 kPa by the amount of H2.

B 1010 kPa They have just divided 20 200 kPa by the amount of N2 or NH3.

C 4040 kPa They have done the calculation for N2 or NH3 instead of H2.

D 12 120 kPa Correct answer: The mole fraction of H2 is 60/100. 60/100 × 20 200 = 12 120.

Your answer

7. Look at the reaction below.

H2NO3+ + H2SO4 NO2

+ + HSO4– + H3O+

Which are a conjugate acid/base pair?

A H2NO3+ and H3O+ Incorrect, they differ by more than one element.

B H2NO3+ and HSO4

– Incorrect, they differ by more than one element.

C H2SO4 and HSO4– Correct answer: They differ by H+.

D H2SO4 and H3O+ Incorrect, they differ by more than one element.


D

Your answer

8. The following reaction is analysed to determine the order of reaction for each reactant.

BrO3–(aq) + 6I–(aq) + 6H+ 3I2(aq) + 3H2O(l) + Br–(aq)

Experiment [BrO3–

(aq)] / mol dm–3

[I–(aq)] / mol dm–3

[H+(aq)] / mol dm–3

Initial rate / mol dm–3 s–1

1 0.1 0.1 0.1 4.8 × 10–3

2 0.2 0.1 0.1 4.8 × 10–3

3 0.2 0.1 0.2 9.6 × 10–3

4 0.2 0.2 0.1 1.9 × 10–2

What are the value and units of the rate constant?

A 0.48 dm3 mol–1 s–1 They have probably used order 1 for I–, looking at the change in rate from experiment 3 to experiment 4 but not taking into account [H+

(aq)].

B 0.48 dm9 mol–3 s–1 Possibly a guess, the units do not match the calculation.

C 4.8 dm–6 mol2 s–1 The calculation is correct but they have determined the units incorrectly.

D 4.8 dm6 mol–2 s–1 Correct answer

Your answer


C

D

9. Ethanoic acid, CH3COOH, has a Ka of 1.7 × 10–5 mol dm–3. It can form a buffer solution when mixed with NaOH.

A student mixes equal amounts of solutions of CH3COOH and NaOH.

Which mixture will give a buffer with pH = 4.77?

[CH3COOH] / mol dm–3 [NaOH] / mol dm–3

A 0.1 0.2

This would not form a buffer as the base is in excess – the pH would be >7.

B 0.1 0.1

This would not form a buffer as the weak acid would be neutralised. The pH would be 7.

C 0.2 0.1

Correct answer: –log(1.7 × 10–5 × (0.2 – 0.1)/0.1)

D 0.3 0.1

Incorrect, this mixture would give a pH of 4.46.

Your answer


C

10. Which of these statements is/are true for the Haber process?

N2 + 3H2 2NH3 H = −92.4 kJ mol–1

1 Increasing the temperature will increase the value of Kc.

2 Increasing the concentration of nitrogen will not change the value of Kc at equilibrium.

3 An iron catalyst will not affect the value of Kc.

A 1, 2 and 3 They may have mistaken the reaction for being endothermic.

B only 1 and 2 They are possibly confusing equilibrium constant with rate constant, for which this combination would be correct.

C only 2 and 3 Correct answer: Increasing the temperature will cause the equilibrium to shift towards the left, giving a small Kc. The value of Kc is not affected by concentration or presence of catalyst.

D only 1 Incorrect, possibly a guess or combination of errors.

Your answer


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Multiple Choice Questions (MCQ) topic quiz


Learner Activity

1. Ka for ethanoic acid is 1.7 × 10–5 mol dm–3 at 25 °C.

What is the pH of a 0.125 mol dm–3 solution of ethanoic acid at this temperature?

A 0.75

B 0.90

C 2.8

D 5.7

Your answer


2. A student monitors the rate of a reaction and plots the concentration of one reactant against time. The shape of the concentration–time graph is shown below.

What can be determined about this reaction?

A The reaction is zero order with respect to this reactant.

B The reaction is first order with respect to this reactant.

C The reaction is second order with respect to this reactant.

D The rate of reaction is constant.

Your answer


3. Carbon monoxide reacts with nitrogen dioxide:

CO(g) + NO2(g) CO2(g) + NO(g)

This reaction follows a two-step mechanism:

2NO2(g) NO3(g) + NO(g) Slow step

CO(g) + NO3(g) CO2(g) + NO2(g) Fast step

What is the correct rate equation for the reaction?

A rate = k[CO][NO3]

B rate = k[NO2]2[CO][NO3]

C rate = k[NO2]2

D rate = k[NO2]2[NO3][NO]

Your answer

4. The Arrhenius equation k = Ae–Ea/RT can be rearranged so it can be represented by a

straight-line graph.

Which expression represents the gradient of the graph?

A –Ea/R

B ln A

C ln k

D 1/T

Your answer


5. A student mixes 6.0 mol of ethanoic acid and 12.5 mol of ethanol and allows an equilibrium

to establish:

CH3COOH(l) + CH3CH2OH(l) CH3COOCH2CH3(l) + H2O(l)

At equilibrium 1 mol of ethanoic acid remains.

Which row gives the correct amounts of each substance at equilibrium?

Amount (in mol) of substance

CH3COOH C2H5OH CH3COOCH2CH3 H2O

A 1 7.5 1 1

B 1 7.5 5 5

C 1 12.5 5 1

D 1 12.5 5 5

Your answer


6. A mixture contains:

20 mol N2(g)

60 mol H2(g)

20 mol NH3(g)

The total pressure is 20 200 kPa.

What is the partial pressure of hydrogen?

A 336.7 kPa

B 1010 kPa

C 4040 kPa

D 12 120 kPa

Your answer

7. Look at the reaction below.

H2NO3+ + H2SO4 NO2

+ + HSO4– + H3O+

Which are a conjugate acid/base pair?

A H2NO3+ and H3O+

B H2NO3+ and HSO4

–

C H2SO4 and HSO4–

D H2SO4 and H3O+

Your answer


8. The following reaction is analysed to determine the order of reaction for each reactant.

BrO3–(aq) + 6I–(aq) + 6H+ 3I2(aq) + 3H2O(l) + Br–(aq)

Experiment [BrO3–(aq)] /

mol dm–3[I–(aq)] / mol dm–3

[H+(aq)] / mol dm–3

Initial rate / mol dm–3 s–1

1 0.1 0.1 0.1 4.8 × 10–3

2 0.2 0.1 0.1 4.8 × 10–3

3 0.2 0.1 0.2 9.6 × 10–3

4 0.2 0.2 0.1 1.9 × 10–2

What are the value and units of the rate constant?

A 0.48 dm3 mol–1 s–1

B 0.48 dm9 mol–3 s–1

C 4.8 dm–6 mol2 s–1

D 4.8 dm6 mol–2 s–1

Your answer


9. Ethanoic acid, CH3COOH, has a Ka of 1.7 × 10–5 mol dm–3. It can form a buffer solution when mixed with NaOH.

A student mixes equal amounts of solutions of CH3COOH and NaOH.

Which mixture will give a buffer with pH = 4.77?

[CH3COOH] / mol dm–3 [NaOH] / mol dm–3

A 0.1 0.2

B 0.1 0.1

C 0.2 0.1

D 0.3 0.1

Your answer


10. Which of these statements is/are true for the Haber process?

N2 + 3H2 2NH3 H = −92.4 kJ mol–1

1 Increasing the temperature will increase the value of Kc.

2 Increasing the concentration of nitrogen will not change the value of Kc at equilibrium.

3 An iron catalyst will not affect the value of Kc.

A 1, 2 and 3

B only 1 and 2

C only 2 and 3

D only 1

Your answer


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