O-LevelChemistryChemistry of the Environment5070/22 · Oct/Nov 2015 · Q36 Marks

Water for use in the home is treated using carbon and chlorine.

(a)Explain the purpose of using carbon and chlorine in water treatment. carbon. chlorine[2]
(b)In some parts of the world, drinking water is purified by desalination. What is meant by the term desalination?[1]
(c)River water may contain pollutants from agricultural sources. These pollutants may cause eutrophication. Give the names of two anions present in fertilisers which contribute to eutrophication.[1]
(d)An aqueous solution of barium chloride is added to a sample of water which contains sulfate ions. A white precipitate forms. Construct an ionic equation, including state symbols, for this reaction.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2015). The mark or mark type is shown in brackets.

[2] (a) carbon for removing smells/removing odours/for removing tastes/so it tastes better (1) chlorine to kill bacteria/to kill microbes/to kill micro-organisms (1)
[1] (b) removal of salt/removal of minerals from (sea) water (1)
[1] (c) nitrate and phosphate (1)
[2] (d) Ba²+(aq) + SO4²¯(aq) → BaSO4(s) (2) 1 mark for correct formulae 1 mark for correct state symbols (dependent on correct formulae)

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