A student investigates a gas produced during an experiment. They suspect the gas may be either chlorine or oxygen. Describe how the student could test for both chlorine and oxygen, and state the positive result for each test.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Test for chlorine: hold damp litmus paper in the gas.
Positive result for chlorine: the paper is bleached / turns white.
Test for oxygen: hold a glowing splint in the gas.
Positive result for oxygen: the splint relights.
Positive result for chlorine: the paper is bleached / turns white.
Test for oxygen: hold a glowing splint in the gas.
Positive result for oxygen: the splint relights.
Examiner tips
- Use the exact wording from the mark scheme: "hold damp litmus paper" and "hold a glowing splint". Mention the colour change for chlorine and the relight for oxygen. Keep the answer concise – 4 points only.
- common_mistakes
- :
- Writing "dry litmus paper" or "dry splint" – the tests require damp litmus and a glowing splint. Forgetting to state the colour change or the relight. Using vague terms like "colour change" instead of the specific outcomes.
Mark scheme (4 marks)
- Test for chlorine: hold damp litmus paper in the gas
- Positive result for chlorine: litmus paper is bleached / turns white
- Test for oxygen: hold a glowing splint in the gas
- Positive result for oxygen: the glowing splint relights
Key terms in this question
Related
- All AQA GCSE Chemistry (8462) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →