An automated testing station checks gas samples for carbon dioxide using fresh, clear limewater. For one sample, the station passes a single small bubble of gas through the limewater. The limewater stays clear, so the station reports that carbon dioxide is absent.
Why could this report be incorrect?
Oxygen is needed as well as carbon dioxide before calcium carbonate can form.
Carbon dioxide must be damp before it can react with the calcium hydroxide.
Too little gas may have passed through for any cloudiness to be seen clearly.
Calcium carbonate dissolves in water, so the limewater would stay clear anyway.
89 exam-style questions on AQA GCSE Chemistry 8.2 Identification of common gases, covering 8.2.1 Test for hydrogen, 8.2.2 Test for oxygen, 8.2.3 Test for carbon dioxide, and 8.2.4 Test for chlorine. Each one has a worked solution and a mark scheme showing where the marks go.