Limewater: A clear, colourless solution of calcium hydroxide (Ca(OH)₂). It turns milky/cloudy in the presence of carbon dioxide due to formation of a white precipitate of calcium carbonate.
Positive result: The specific, characteristic observation that confirms the presence of a particular substance in a test.
Bleaching: The destruction of colour in a substance, often by oxidation. Chlorine bleaches damp litmus paper because it forms hypochlorous acid which oxidises the dye molecules.
Combustion: A reaction in which a substance reacts rapidly with oxygen, releasing energy as heat and light.
This definitions covers Key Definitions 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 7 of 13 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
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.