Edexcel IGCSE Chemistry (b) Rates of reaction

[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 (b) Rates of reaction 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.

Edexcel IGCSE Chemistry (b) Rates of reaction Question Bank

Exam points

Covered syllabus points

Covered syllabus points

(b) Rates of reaction question 1

Question (a)

Question (b)

Question (c)

Question (d)

Question (e)

(b) Rates of reaction question 2

(b) Rates of reaction question 3