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IGCSE · Practice questions · Rate of reaction

Read the gradient.

Six original Cambridge-style questions on rate of reaction: practical methods, rate graphs, mean rate calculations and the factors that change the rate.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
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Steeper means faster.

01
Recall
[3 marks]

Describe how you could measure the rate of the reaction between magnesium ribbon and dilute hydrochloric acid.

  • Add the magnesium to the acid in a conical flask connected to a gas syringe. ✓
  • Start a stopwatch and record the volume of hydrogen at regular intervals, for example every 10 s. ✓
  • Plot volume of gas against time; the gradient shows the rate. ✓
02
Analysis
[3 marks]

In a reaction, the volume of gas collected was 0, 24, 40, 50, 55, 56 and 56 cm3 at 0, 10, 20, 30, 40, 50 and 60 s. (a) Calculate the mean rate in the first 20 s. (b) State when the reaction finished and explain how you know.

  • (a) 40 ÷ 20 = 2 cm3/s. ✓
  • (b) At about 50 s, ✓
  • because the volume stops increasing (it stays at 56 cm3). ✓
03
Explain
[2 marks]

Explain why the rate of a reaction is fastest at the start and then slows down.

  • At the start the concentration (or amount) of reactants is highest. ✓
  • As reactants are used up their concentration falls, so the reaction slows and finally stops. ✓
04
Analysis
[3 marks]

Marble chips react with excess dilute hydrochloric acid. Sketch, on the same axes, the graph of volume of carbon dioxide against time for (a) large chips and (b) the same mass of powdered marble. Explain the differences.

  • The powder curve is steeper at the start: faster reaction. ✓
  • Both curves level off at the same final volume. ✓
  • The powder has a larger surface area, but the mass of marble (the limiting reactant) is the same, so the same amount of gas forms. ✓
05
Recall
[2 marks]

State two ways, other than using a catalyst, of increasing the rate of reaction between zinc and dilute sulfuric acid.

  • Increase the concentration of the acid. ✓
  • Increase the temperature, or use zinc powder instead of larger pieces. ✓
06
Explain
[3 marks]

Describe how you would show that copper(II) oxide is a catalyst for the decomposition of hydrogen peroxide.

  • Compare the rate of oxygen production with and without a weighed mass of copper(II) oxide: it is faster with the oxide. ✓
  • At the end, filter off the copper(II) oxide, wash and dry it and weigh it again. ✓
  • The same mass is recovered, showing it is unchanged, so it is a catalyst. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.