What is a disproportionation reaction?
Disproportionation is a redox reaction in which the same element is both oxidised and reduced.
The reaction of chlorine with water is an example of disproportionation: Cl2 + H2O ➔ HClO + HCl.
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Explain, with the use of an equation, the role of chlorine in water treatment.
Chlorine is used in water purification as a sterilising agent. When chlorine is added to water, chloric(I) acid (HClO) is formed which kills harmful bacteria.
Cl2(aq) + H2O(l) ➔ HClO(aq) + HCl(aq)
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Explain, with the use of an equation, why outdoor swimming pools need frequent additions of chlorine.
Shallow swimming pools require frequent additions of chlorine because chlorine is rapidly lost in sunlight as it reacts with water to form hydrochloric acid and oxygen.
Cl2(g) + H2O(l) ➔ 2HCl(aq) + 1⁄2O2(g)
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Give one benefit and one risk of using chlorine in water treatment?
Benefit: Chlorine ensures safe drinking water by killing bacteria.
Risk: Chlorine is toxic in high concentrations and can react with organic compounds to form potentially harmful chlorinated hydrocarbons.
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Explain, with the use of an equation, the role of chlorine in the preparation of bleach.
Sodium chlorate(I) (NaClO) is an active ingredient in bleach. It is formed from the disproportionation reaction of chlorine with cold, dilute aqueous sodium hydroxide.
Cl2(aq) + 2NaOH(aq) ➔ NaClO(aq) + NaCl(aq) + H2O(l)
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