Knowledge Organiser: Gas Tests
Part of Gas Tests · GCSE GCSE Chemistry revision
This topic summary covers Knowledge Organiser: Gas Tests within Gas Tests for GCSE Chemistry. Revise Gas Tests in Chemical Analysis for GCSE Chemistry with 20 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 13 of 13 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 13 of 13
Practice
20 questions
Recall
15 flashcards
Knowledge Organiser: Gas Tests
Hydrogen
- Test: burning (lit) splint held to mouth of tube
- Result: squeaky pop (H₂ ignites explosively)
- Equation: 2H₂ + O₂ → 2H₂O
- Note: BURNING splint — NOT glowing (that is oxygen)
Oxygen
- Test: glowing splint
- Result: splint relights
- Explanation: supports combustion
- Note: GLOWING not burning
Carbon Dioxide
- Test: bubble through limewater
- Result: turns milky/cloudy
- Product: CaCO₃ (white precipitate)
- Excess CO₂ clears the solution
Chlorine and Ammonia
- Cl₂: damp BLUE litmus → bleaches white
- NH₃: damp RED litmus → turns blue
- NH₃ also: white fumes with HCl rod
- Both need DAMP litmus
Key Equations
- 2H₂ + O₂ → 2H₂O (hydrogen combustion — squeaky pop)
- CO₂ + Ca(OH)₂ → CaCO₃ + H₂O (CO₂ turns limewater milky)
- NH₃ + HCl → NH₄Cl (white fumes of ammonium chloride)
Common Mistakes
- Using a burning splint for oxygen: The oxygen test uses a GLOWING (not burning) splint — a glowing splint relights in oxygen
- Saying limewater turns white for any gas: Only CO₂ turns limewater milky/cloudy — other gases do not react with Ca(OH)₂
- Using dry litmus for chlorine/ammonia: Both tests require DAMP litmus paper — dry litmus does not respond to these gases
- Confusing chlorine and ammonia litmus tests: Chlorine bleaches litmus (any colour → white); ammonia turns red litmus → blue (alkaline)
Revise this topic interactively on PrepWise — self-test mode, tap-to-reveal definitions, and Common Mistakes from examiners.
Try the interactive Knowledge Organiser — free →Keep building this topic
Read this section alongside the surrounding pages in Gas Tests. That gives you the full topic sequence instead of a single isolated revision point.
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.
Quick Recall Flashcards
20 questions on Gas Tests — practise free
Instant marking, adaptive difficulty, and 15 spaced repetition flashcards. Free until your GCSEs.
Try PrepWise Free