Cambridge O Level Chemistry · Syllabus 5070 · Experimental Techniques and Chemical Analysis
Gas Test
What is Gas Test?
A test that identifies a gas from a single characteristic result. Six are required: ammonia turns damp red litmus paper blue; carbon dioxide turns limewater milky; chlorine bleaches damp litmus paper; hydrogen pops with a lighted splint; oxygen relights a glowing splint; and sulfur dioxide turns acidified aqueous potassium manganate(VII) from purple to colourless. The test material is held at the mouth of the vessel or the gas is bubbled through the solution; a gas is never smelled directly.
This definition is part of the Experimental Techniques and Chemical Analysis chapter in Cambridge O Level Chemistry.
Common mistakes with Gas Test
- 17. “It turns red litmus paper blue, so it is ammonia.” Why it fails The official test specifies damp red litmus paper, and dry paper may show nothing at all. Correct Turns damp red litmus paper blue. Check Which other gas test specifies damp paper? Chlorine — it bleaches damp litmus paper.
Reviewed by Academiq Edu Instructor PanelLast reviewed Syllabus 2026-2028