Edexcel IGCSE Chemistry B Rates of Reaction Questions

Practise interpreting rate experiments using curves, gradients, catalysts, controls and particle-collision explanations.

Exam points

calculate reaction rate from a tangent gradient and give correct units
draw rate curves showing steeper starts, lower gradients or the same final volume
explain rate changes using collisions, activation energy, catalyst pathways and controlled variables

Covered syllabus points

3.9 Experiments on factors affecting reaction rate 3.10 Effects of factors on reaction rate 3.11 Collision theory and reaction rate 3.12 Catalyst definition 3.13 Catalysts and activation energy 3.14C Reaction profile diagrams 3.15 Surface area and concentration rate practical 3.16 Catalytic decomposition practical

[Maximum number: 9]

Dilute hydrochloric acid reacts with a solution of sodium thiosulfate $\left(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\right)$ to form a precipitate.

The equation for the reaction is

\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}(\mathrm{aq})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow 2 \mathrm{NaCl}(\mathrm{aq})+\mathrm{S}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{SO}_{2}(\mathrm{~g})

(a)

The reaction is often used to investigate rates of reaction.

The diagram shows the apparatus a student uses to investigate the effect of temperature on the rate of the reaction.

Figure for Question (a) — Edexcel IGCSE Chemistry

This is the student's method.
- pour $50 \mathrm{~cm}^{3}$ of cold sodium thiosulfate solution into a conical flask and heat it to $20^{\circ} \mathrm{C}$
- draw a cross ( X ) on a piece of paper and place it under the flask
- add $5 \mathrm{~cm}^{3}$ of dilute hydrochloric acid to the flask
- look at the cross from above and record the time taken until the cross cannot be seen

The student repeats the experiment four times, using sodium thiosulfate solution at a different temperature each time.

He keeps the volumes of sodium thiosulfate solution and hydrochloric acid constant in each experiment.

Give two other factors that the student should keep constant.

1
2

[ 2 ]

(b)

The table shows the student's results.

Table for Question (b) — Edexcel IGCSE Chemistry

The highest temperature the student uses is 60 °C because he thinks the results might not be as accurate at temperatures higher than 60 °C.

Suggest a reason why the results might not be as accurate at temperatures higher than 60 °C.

[ 1 ]

(c)

Calculate the time that it would take for the cross not to be seen at 45 °C.

time = ................................ s

[ 2 ]

(d)

Describe the relationship between rate of reaction and temperature shown by the graph.

[ 1 ]

(e)

Explain, in terms of particle collision theory, the effect that increasing the temperature has on the rate of a reaction.

[ 3 ]

[Maximum number: 1]

This question is about magnesium metal and its compounds.

A student uses this method to make a solution of magnesium chloride.

Step 1. measure $25 \mathrm{~cm}^{3}$ of dilute hydrochloric acid into a beaker
Step 2 add magnesium powder a little at a time
Step 3 keep adding magnesium powder until it is in excess
Step 4 remove the excess magnesium powder by filtration

This is the equation for the reaction.

Figure for Question 2 — Edexcel IGCSE Chemistry

Give a reason why the student uses magnesium powder rather than magnesium ribbon.

[Maximum number: 3]

A student investigates the effect of temperature on the rate of reaction between two solutions, A and B . When the reaction occurs, the mixture turns from colourless to blue.

This is the student's method.
- pour $25 \mathrm{~cm}^{3}$ of solution A into a conical flask
- add solution B and measure the temperature of the mixture
- record the time taken for the mixture to turn blue

The student repeats this method at different temperatures.

Explain how increasing the temperature affects the rate of a reaction.

Refer to particle collision theory in your answer.

[Maximum number: 1]

Hydrogen peroxide solution decomposes slowly at room temperature to form water and oxygen.

The equation for the reaction is

2 \mathrm{H}_{2} \mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}

A catalyst increases the rate of this reaction.

State one other property of a catalyst.

[Maximum number: 2]

A student uses this apparatus to investigate the decomposition of hydrogen peroxide solution.

Figure for Question 5 — Edexcel IGCSE Chemistry

This is the equation for the reaction.

2 \mathrm{H}_{2} \mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}

In this reaction, the manganese(IV) oxide acts as a catalyst.

Explain how a catalyst works.

[Maximum number: 2]

Hydrogen peroxide solution decomposes slowly at room temperature to form water and oxygen.

The equation for the reaction is

2 \mathrm{H}_{2} \mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}

The decomposition of hydrogen peroxide solution is exothermic.

On the diagram, draw and label the reaction profiles for the reaction
- without a catalyst
- with a catalyst

Figure for Question 6 — Edexcel IGCSE Chemistry

[Maximum number: 2]

A student uses this apparatus to investigate the rate of reaction between marble chips and dilute hydrochloric acid.

Figure for Question 7 — Edexcel IGCSE Chemistry

This is the equation for the reaction.

\mathrm{CaCO}_{3}(\mathrm{~s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{CO}_{2}(\mathrm{~g})

(a)

Give a reason why the reading on the balance decreases during the reaction.

[ 1 ]

(b)

After 10 minutes, the reaction stops even though there are marble chips remaining.

Give a reason why the reaction stops.

[ 1 ]

[Maximum number: 5]

A student uses this apparatus to investigate the decomposition of hydrogen peroxide solution.

Figure for Question 8 — Edexcel IGCSE Chemistry

This is the equation for the reaction.

2 \mathrm{H}_{2} \mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}

Potassium iodide has been suggested as an alternative catalyst to manganese(IV) oxide.

Describe a method to show which catalyst is more effective for the decomposition of hydrogen peroxide.

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Covered syllabus points

Question 1

Question (a)

Question (b)

Question (c)

Question (d)

Question (e)

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question (a)

Question (b)

Question 8