Ammonia, NH3 / The test for ammonia gas
2 marks · EasyA student carries out a test for ammonia gas using damp red litmus paper. The student expects to see the colour of the paper change. If the student starts with 5 pieces of damp red litmus paper and plans one test for each of 5 gas samples, how many pieces of red litmus paper will change colour if all 5 samples are ammonia gas? State the final colour of the litmus paper.
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5 pieces; all turn blue
Also accept: 5; blue; five pieces; blue; all 5 turn blue; five, all turn blue; 5, blue; all the papers turn blue
Common mistakes: State only the number without the colour; State wrong colour (e.g. purple or red); Write 1 instead of 5
Show mark scheme and worked solution
Marking points
M1 · 1 mark · States that 5 pieces of litmus paper change colour (5, five, or equivalent).
A1 · 1 mark · States that the litmus paper turns blue.
Worked solution
Since there are 5 samples and each is tested with a piece of red litmus paper, 5 pieces are used in total.
Ammonia gas turns damp red litmus paper blue.
Therefore, all 5 pieces of litmus paper will turn blue.