CAIE A Level Chemistry 9701 · Group 17
In the treatment of drinking water, chlorine gas is added to kill harmful bacteria. Explain, using relevant equations and oxidation numbers, how chlorine produces the active disinfecting species HOCl and ClO- in water and why this reaction is an example of disproportionation.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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