CC9.2Tests for gases: hydrogen, oxygen, carbon dioxide, ammonia, chlorine

Notes

Gas	Test	Positive result
Hydrogen (H₂)	Hold lit splint to mouth of test tube	"Squeaky pop"
Oxygen (O₂)	Insert glowing splint	Splint relights
Carbon dioxide (CO₂)	Bubble through limewater	Turns milky/cloudy
Ammonia (NH₃)	Hold damp red litmus paper near gas	Turns blue (alkaline)
Chlorine (Cl₂)	Hold damp litmus paper near gas	Bleaches it white

H₂: produced when metals react with acids; electrolysis of water.
O₂: produced in electrolysis; thermal decomposition of hydrogen peroxide; photosynthesis.
CO₂: produced in combustion; acid + carbonate; fermentation; respiration.
NH₃: produced when ammonium compounds are heated with an alkali.
Cl₂: produced in electrolysis of brine; displacement reactions of halogens.

Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)

CaCO₃ is insoluble → white precipitate → limewater turns milky.

If excess CO₂ is bubbled, the precipitate may dissolve (Ca(HCO₃)₂ forms — soluble).

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Try each before peeking at the worked solution.

Question 15 marks
Gas tests quiz
(5 marks) Name the gas and describe the test for each:

(a) A colourless gas that turns damp red litmus paper blue.
(b) A gas that causes a glowing splint to relight.
(c) A gas that turns limewater milky.
(d) A gas that causes a lit splint to "pop".
(e) A gas that bleaches damp litmus paper white.
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AI-generated · claude-opus-4-7 · v3-edexcel-combined-science
Question 22 marks
Limewater test equation
(2 marks) Write the ionic equation for the reaction of carbon dioxide with limewater. State what is observed.
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CC9.2 — Tests for gases

5-card SR deck for Edexcel Combined Science topic CC9.2

5 cards · spaced repetition (SM-2)