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WAEC Chemistry 2018 Paper

Question : 31

Total: 50

Solution:

Concept:

Chlorine reacts with water to form acidic products, which lowers the pH.

Explanation:

When chlorine gas is dissolved in water, it undergoes a disproportionation reaction:

\mathrm{Cl}_{2} + \mathrm{H}_{2}\mathrm{O} \rightarrow \mathrm{HCl} + \mathrm{HOCl}

Hydrochloric acid (

\mathrm{HCl}

) and hypochlorous acid (

\mathrm{HOCl}

) are both acids.

Their presence makes the resulting solution acidic.

Therefore, the pH of the water sample becomes less than 7.

Answer:

< 7

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