"POP = Hydrogen, RELIGHT = Oxygen, MILKY = CO₂, BLEACH = Chlorine"
Or remember it as a story: "Hydrogen POPS, Oxygen RELIGHTS, CO₂ CLOUDS limewater, Chlorine BLEACHES"
For the litmus confusion: "BLUE bleaches (chlorine), RED turns blue (ammonia)" — opposite colours, opposite results.
Quick Check: A student bubbles a gas through limewater and the solution turns milky. Name the gas and write the ionic equation for the reaction.
The gas is carbon dioxide (CO₂). Equation: CO₂(g) + Ca(OH)₂(aq) → CaCO₃(s) + H₂O(l)
This memory aid covers Memory Aid 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 9 of 13 in this topic. Use it for quick recall, then test yourself straight afterwards so the memory aid becomes usable in an answer.
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.