A student shakes the same gas with limewater three times and the limewater turns milky every time. The student says the repeats prove that the gas is carbon dioxide. What is wrong with this statement?
Nothing is wrong, because repeating a test proves a result.
Repeats show the result is repeatable, not that it is correct.
The test must be repeated at least five times to be valid.
Limewater gives a different result each time it is used.
40 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.