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.
🎯 Exam Focus
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.
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.