Very High Frequency
What Examiners Ask About Gas Tests
- "Describe the test for hydrogen/oxygen/CO₂/chlorine" — state method AND positive result (2 marks each)
- "Explain why limewater turns milky" — must mention CaCO₃ precipitate (2 marks)
- "Why must the litmus paper be damp?" — water needed for the reaction with chlorine (1 mark)
- "What is the difference between the hydrogen and oxygen tests?" — burning vs glowing splint (2 marks)
- Write or complete the equation for one of the gas test reactions (2 marks)
Marks at Risk
- Saying "burning splint" for oxygen — always "glowing splint"
- Vague descriptions — say exactly "squeaky pop", "relights", "turns milky", "bleaches white"
- Forgetting "damp" for chlorine and ammonia tests
Edexcel 1CH0: Examined in Paper 2 (1CH0/2). Edexcel CP11 covers tests for hydrogen, oxygen, carbon dioxide, ammonia, and chlorine — you must know reagents, conditions, and observations for all five. In Edexcel-style questions, the command word "Suggest" appears frequently — use your chemistry knowledge to apply to an unfamiliar context.
This exam focus covers Exam Focus within Gas Tests for GCSE Chemistry. Revise Gas Tests in Chemical Analysis for GCSE Chemistry with 20 exam-style questions and 15 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 11 of 13 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Practice questions for Gas Tests
Which observation confirms a gas is hydrogen when tested with a burning splint?
Explain why hydrogen gas produces a squeaky pop when tested with a burning splint.