State two signs that a sample of water is not pure, and for each sign, identify the dissolved substance or type of contamination responsible.

Cambridge International IGCSE Chemistry (0620) — 10.1 Water · State · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

1. The water is coloured or turbid – caused by dissolved minerals or suspended particles.
2. The water has an unpleasant odour – caused by dissolved gases such as hydrogen sulfide.

Examiner tips

Use the exact wording ‘coloured’, ‘turbid’, ‘unpleasant odour’ – examiners look for these terms.
Pair each sign with the correct cause (minerals/particles for colour, gases for odour).

Common mistakes

Using vague terms like ‘dirty’ instead of ‘turbid’. Failing to match the correct cause to the sign (e.g., saying ‘chlorine’ for colour).

Mark scheme (4 marks)

Sign 1: the water has a colour / is coloured / is discoloured / is not clear / is turbid
Cause of sign 1: dissolved minerals / suspended particles / sediment / organic matter / heavy metal ions
Sign 2: the water has an unpleasant smell / odour / taste (different from sign 1)
Cause of sign 2: dissolved gases / microorganisms / sewage / pollutants / chlorine / hydrogen sulfide

Key terms in this question

contamination