AQA · Chemistry · 8462
GCSE Chemistry (AQA): Tests for Gases
Topic 8 — Chemical Analysis. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Testing for Gases - Hydrogen/Chlorine/Oxygen/CO2 (2027/28 exams)"; each card deep-links to the moment in the video it came from. Lesson 8.03 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_8.03.
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Which chemical is limewater a solution of?
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Aqueous calcium hydroxide, Ca(OH)₂.
Why does limewater turn cloudy when carbon dioxide is bubbled through it?
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Insoluble solid calcium carbonate is formed, and its suspended particles make the solution appear cloudy.
Which product is formed during the squeaky pop test for hydrogen?
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Water — the hydrogen burns with oxygen from the air.
What safety precaution is needed when testing for chlorine?
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Work in a fume cupboard (or wear a mask), because chlorine is poisonous.
Why can damp blue litmus paper briefly turn red in the chlorine test?
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Chlorine dissolves in the water on the paper to form hydrochloric acid, which is acidic. The paper is then bleached white.
What is the chemical test for hydrogen gas?
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A burning (lit) splint held near the gas produces a squeaky pop.
What is the chemical test for oxygen gas?
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A glowing splint placed in the gas relights.
What is the chemical test for chlorine gas?
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Damp blue litmus paper is placed in the gas; it is bleached white.
What is the chemical test for carbon dioxide?
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Bubble the gas through limewater; it turns cloudy (milky).
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