A student set up an apparatus to determine the percentage of oxygen in the atmosphere. They passed 120 cm3120\text{ cm}^3120 cm3 of air repeatedly over a heated sample of copper powder in a sealed tube connected to two gas syringes.
At the end of the experiment, after the apparatus had cooled to room temperature, the volume of gas in the syringes was 108 cm3108\text{ cm}^3108 cm3. Analysis of the remaining gas showed that it still contained some oxygen.
Suggest one reason why not all of the oxygen in the air sample reacted with the copper.
97 exam-style questions on Edexcel GCSE Chemistry 9.2 Earth and atmospheric science, covering 9.2.1 The Earth's early atmosphere, 9.2.2 How the atmosphere evolved, 9.2.3 Chemical test for oxygen, and 9.2.4 The greenhouse effect and climate change. Each one has a worked solution and a mark scheme showing where the marks go.