Ammonia, NH3 / The test for ammonia gas
2 marks · EasyA water sample was tested and its boiling point found to be 101.5°C at 1 atmosphere pressure. Calculate by how much the boiling point differs from that of pure water. Is the sample likely to be pure?
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1.5 °C (±0.1)
Also accept: 1.5°C
Common mistakes: Subtracting 101.5 from 0; Saying the sample is pure
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Marking points
M1 · 1 mark · Subtracts 100°C from 101.5°C to find the difference. (follow-through)
A1 · 1 mark · States 1.5°C as the difference (or recognises the sample is not pure). (follow-through)
Worked solution
The boiling point is 1.5°C higher than pure water, so the sample is not pure.