Rates of Reaction Practice Questions

Question 1

4 marks

Hydrogen peroxide solution decomposes slowly at room temperature.

$2\mathrm{H_2O_2(aq)} \rightarrow 2\mathrm{H_2O(l)} + \mathrm{O_2(g)}$

A student adds $0.50\ \mathrm{g}$ of manganese(IV) oxide powder to $50\ \mathrm{cm^3}$ of hydrogen peroxide solution. Bubbles of oxygen are produced quickly.

(a)

Manganese(IV) oxide is a catalyst for this reaction.

State the effect of the catalyst on the rate of this reaction.

/ 1

(b)

At the end of the reaction the mixture is filtered. The manganese(IV) oxide is washed, dried and weighed.

Predict the mass of manganese(IV) oxide obtained and explain your answer.

/ 2

(c)

Enzymes are biological catalysts.

State one use of enzymes in industry.

/ 1

Question 2

4 marks

Zinc reacts with dilute sulfuric acid to produce hydrogen gas.

$\mathrm{Zn(s)} + \mathrm{H_2SO_4(aq)} \rightarrow \mathrm{ZnSO_4(aq)} + \mathrm{H_2(g)}$

(a)

State what must happen to particles of zinc and particles of acid for a reaction to take place.

/ 2

(b)

The experiment is repeated using the same mass of powdered zinc instead of zinc granules. All other conditions are kept the same.

Explain why the rate of reaction is greater with the powdered zinc.

/ 2

Question 3

3 marks

A student adds an excess of marble chips (calcium carbonate) to $25\ \mathrm{cm^3}$ of dilute hydrochloric acid. The gas produced is collected in a gas syringe.

The reaction stops after $80\ \mathrm{s}$ , when $48\ \mathrm{cm^3}$ of gas has been collected.

(a)

Name the gas collected in the gas syringe.

/ 1

(b)

Calculate the mean rate of reaction, in $\mathrm{cm^3\ s^{-1}}$ .

mean rate of reaction = .............................................. $\mathrm{cm^3\ s^{-1}}$

/ 2

Question 0

7 marks

Sodium thiosulfate solution reacts with dilute hydrochloric acid to form a pale yellow precipitate of sulfur.

$\mathrm{Na_2S_2O_3(aq)} + 2\mathrm{HCl(aq)} \rightarrow 2\mathrm{NaCl(aq)} + \mathrm{S(s)} + \mathrm{SO_2(g)} + \mathrm{H_2O(l)}$

A student investigates how temperature affects the rate of this reaction. The results are shown in the table.

temperature in °C	20	30	40	50	60
time for the cross to disappear in s	96	62	41	28	19

(a)

Describe how the student obtained the times shown in the table.

/ 2

(b)

The rate of reaction can be given by $\dfrac{1}{t}$ , where $t$ is the time for the cross to disappear.

Calculate the rate of reaction at $50\ ^{\circ}\mathrm{C}$ , in $\mathrm{s^{-1}}$ , and explain why a shorter time means a faster rate.

/ 2

(c)

Explain, in terms of particles, why increasing the temperature decreases the time for the cross to disappear.

/ 2

(d)

State one variable, other than temperature, that must be kept the same in each experiment.

/ 1

Question 0

6 marks

A student investigates how the concentration of hydrochloric acid affects the rate of reaction with marble chips.

The apparatus the student has set up so far is shown in the diagram. The volume of carbon dioxide produced is to be measured every 20 seconds.

(a)

Describe what should be added to the open end of the delivery tube so that the volume of gas produced can be measured.

/ 2

(b)

Give one reason why a gas syringe gives a more accurate measurement of the volume of carbon dioxide than collecting the gas over water.

/ 1

(c)

For this investigation, state

(i) the independent variable

(ii) the dependent variable

(iii) one control variable.

/ 3

Question 0

7 marks

A student places a conical flask containing dilute hydrochloric acid and an excess of magnesium carbonate on a balance. The flask is left open to the air.

The mass of the flask and its contents is recorded every 30 seconds.

time in s	0	30	60	90	120	150	180
mass of flask and contents in g	125.00	124.56	124.28	124.12	124.04	124.00	124.00

(a)

Explain why the mass of the flask and its contents decreases.

/ 2

(b)

Calculate the mean rate of loss of mass during the first $60\ \mathrm{s}$ , in $\mathrm{g\ s^{-1}}$ .

mean rate = .............................................. $\mathrm{g\ s^{-1}}$

/ 2

(c)

Explain why the rate of loss of mass decreases as the reaction proceeds.

/ 2

(d)

State how the results show that the reaction had finished by $150\ \mathrm{s}$ .

/ 1

Question 0

5 marks

A student adds $0.12\ \mathrm{g}$ of magnesium ribbon to $50\ \mathrm{cm^3}$ of $0.5\ \mathrm{mol\ dm^{-3}}$ hydrochloric acid at $20\ ^{\circ}\mathrm{C}$ . The acid is in excess.

The volume of hydrogen produced is measured using a gas syringe and a graph of volume of hydrogen against time is plotted. The reaction is complete after $90\ \mathrm{s}$ , when $120\ \mathrm{cm^3}$ of hydrogen has been collected.

(a)

Explain why no more hydrogen is produced after $90\ \mathrm{s}$ .

/ 1

(b)

The experiment is repeated using $50\ \mathrm{cm^3}$ of $1.0\ \mathrm{mol\ dm^{-3}}$ hydrochloric acid. All other conditions are kept the same.

Describe how the curve obtained would differ from the original curve.

/ 2

(c)

The original experiment is repeated using $0.06\ \mathrm{g}$ of magnesium ribbon and $50\ \mathrm{cm^3}$ of $0.5\ \mathrm{mol\ dm^{-3}}$ hydrochloric acid at $20\ ^{\circ}\mathrm{C}$ .

Describe how the curve obtained would differ from the original curve.

/ 2

Question 0

8 marks

A student is asked to plan investigations into the rates of two different reactions.

Reaction A: magnesium ribbon reacts with dilute sulfuric acid to produce hydrogen gas.

Reaction B: colourless lead(II) nitrate solution reacts with colourless potassium iodide solution to form a yellow precipitate of lead(II) iodide.

(a)

Suggest a method the student could use to follow the rate of Reaction A.

/ 2

(b)

Explain why measuring the loss in mass of the reaction mixture would not be a suitable method for following Reaction A.

/ 2

(c)

Suggest a method the student could use to follow the rate of Reaction B.

/ 2

(d)

Give one risk in carrying out Reaction A and state a suitable precaution for that risk.

/ 2

Question 0

6 marks

Hydrogen peroxide solution decomposes to form water and oxygen.

$2\mathrm{H_2O_2(aq)} \rightarrow 2\mathrm{H_2O(l)} + \mathrm{O_2(g)}$

A catalyst is added to $50\ \mathrm{cm^3}$ of hydrogen peroxide solution and the volume of oxygen produced is recorded. The graph shows the results. A tangent has been drawn to the curve at $30\ \mathrm{s}$ . The tangent passes through the points $(10\ \mathrm{s},\ 21\ \mathrm{cm^3})$ and $(50\ \mathrm{s},\ 69\ \mathrm{cm^3})$ .

(a)

Use the tangent to calculate the rate of reaction at $30\ \mathrm{s}$ .

rate of reaction = .............................................. $\mathrm{cm^3\ s^{-1}}$

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(b)

The volume of $1\ \mathrm{mol}$ of any gas at room temperature and pressure is $24\ 000\ \mathrm{cm^3}$ .

Calculate the rate of reaction at $30\ \mathrm{s}$ in $\mathrm{mol\ s^{-1}}$ .

rate of reaction = .............................................. $\mathrm{mol\ s^{-1}}$

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(c)

Explain why the rate of reaction at $90\ \mathrm{s}$ is lower than the rate at $30\ \mathrm{s}$ .

/ 2

Question 0

6 marks

A student investigates the reaction between calcium carbonate and dilute hydrochloric acid.

$\mathrm{CaCO_3(s)} + 2\mathrm{HCl(aq)} \rightarrow \mathrm{CaCl_2(aq)} + \mathrm{H_2O(l)} + \mathrm{CO_2(g)}$

In each experiment the student uses $5.0\ \mathrm{g}$ of calcium carbonate (an excess) and $50\ \mathrm{cm^3}$ of acid at $20\ ^{\circ}\mathrm{C}$ , and records the time taken to collect $50\ \mathrm{cm^3}$ of carbon dioxide in a gas syringe.

	experiment 1	experiment 2	experiment 3
form of calcium carbonate	large chips	small chips	small chips
concentration of acid in $\mathrm{mol\ dm^{-3}}$	1.0	1.0	2.0
time to collect $50\ \mathrm{cm^3}$ of gas in s	240	95	40

Use the results of these experiments to explain, in terms of the behaviour of particles, the effect of changing the size of the calcium carbonate pieces and the effect of changing the concentration of the acid on the rate of this reaction.

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Question 0

7 marks

A student investigates how the concentration of hydrogen peroxide solution affects the rate of its decomposition. The same mass of manganese(IV) oxide catalyst is added each time, and the student records the time taken to collect $20\ \mathrm{cm^3}$ of oxygen.

concentration of hydrogen peroxide in %	1.0	2.0	3.0	4.0	5.0
time to collect $20\ \mathrm{cm^3}$ of oxygen in s	120	60	52	30	24

(a)

The student plots the results and draws a line of best fit.

Identify the anomalous result and explain how the student can tell that it is anomalous.

/ 2

(b)

Suggest one reason for this anomalous result.

/ 1

(c)

Calculate the mean rate of production of oxygen, in $\mathrm{cm^3\ s^{-1}}$ , in the experiment using the $5.0\%$ solution.

mean rate = .............................................. $\mathrm{cm^3\ s^{-1}}$

/ 2

(d)

Explain how the manganese(IV) oxide increases the rate of decomposition of hydrogen peroxide.

/ 2

Atomic Structure

States of Matter & Mixtures

Chemical changes

Extracting metals & equilibria

Separate Chemistry 1

Groups in the periodic table

Rates of reaction & energy changes

Fuels & Earth science

Separate Chemistry 2

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