Ammonia, NH3 / The test for ammonia gas
2 marks · NormalState the result of the test for ammonia gas using damp red litmus paper. Explain why this result occurs.
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The red litmus paper turns blue. This occurs because ammonia is an alkaline gas.
Also accept: The red litmus paper changes to blue. This shows ammonia is alkaline.
Common mistakes: Litmus turns red; Indicator turns green; No explanation of alkalinity
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Marking points
B1 · 1 mark · Red litmus paper turns blue (or universal indicator paper turns blue).
B2 · 1 mark · Explanation for result: ammonia is alkaline.
Worked solution
Red litmus paper turns blue in the presence of ammonia gas.
This is because ammonia is an alkaline gas, which causes the paper to change colour.