Describe how you would test for each of the following gases, and state the positive result in each case: hydrogen, oxygen, and carbon dioxide.

AQA GCSE Chemistry (8462) — 4.8.2 Identification of common gases · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

1. Hydrogen – hold a lit splint to the mouth of the test tube. 2. Positive result – a squeaky pop.
3. Oxygen – insert a glowing splint into the gas.
4. Positive result – the glowing splint relights / reignites.

Examiner tips

Use the exact wording: "hold a lit splint" and "insert a glowing splint". Mention the specific positive result for each gas. Keep the answer short and to the point to fit the 4 marks.

Common mistakes

Writing "burning splint" instead of "lit splint". Forgetting to state the positive result. Using the wrong test for oxygen (e.g., a match instead of a glowing splint).

Mark scheme (4 marks)

Test for hydrogen: hold a lit splint to the gas / at the mouth of the test tube
Positive result for hydrogen: squeaky pop (sound)
Test for oxygen: insert a glowing splint into the gas
Positive result for oxygen: the glowing splint relights / reignites

Key terms in this question

hydrogen · oxygen · carbon dioxide