What this practice covers
These questions are drawn from past CIE 0620 Chemistry papers and filtered to water. You answer, you find out immediately whether you were right, and you get the reasoning for the correct option and for each distractor. Wrong answers go to a mistakes locker so you can come back to exactly those.
Practice is free. You need an account only so your progress and your mistakes are still there next time.
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What examiners see students get wrong here
These are the errors that cost marks on water, taken from our own topic notes. Read them before you practise and you will recognise the traps in the questions.
- Saying a colour change with cobalt chloride paper proves the liquid is pure water. It proves only that water is present.
- Forgetting the word anhydrous, so the reagent described has no colour change left to give.
- Giving the colour change backwards: cobalt(II) chloride goes blue to pink, copper(II) sulfate goes white to blue.
- Saying an impurity raises the melting point. It lowers it, and raises the boiling point.
- Saying nitrates poison fish directly, rather than following the algae, light, bacteria and oxygen chain.
- Saying filtration removes dissolved substances. It removes only insoluble solids.
- Saying chlorine is added to remove the taste. Carbon removes tastes and odours; chlorine kills microbes.
- Claiming treated tap water is pure. It still holds dissolved ions, which is why practical work uses distilled water.
Revise it first
If any of the above is unfamiliar, work through the notes before practising: Water revision notes.