Ncert Exercises & Solutions

What happens in the extraction of chlorine by electrolysis of brine?

1. Oxidation of $C l^{-}$ ion to chlorine gas occurs.

2. Reduction of $C l^{-}$ ion to chlorine gas occurs.

3. For overall reaction $∆ G °$ has negative value.

4. A displacement reaction takes place.

HINT: Oxidation of

C l^{-}

ion to chlorine gas occurs.

Explanation:

Following reaction takes place in the extraction of chlorine by electrolysis :

2 H_{2} O (l) + 2 C l^{-} (a q) \to H_{2} (g) + C l_{2} + 2 O H^{-} (a q)

From the above reaction it is very clear that the oxidation of

C l^{-}

ion to chlorine gas occurs. Thus, option (1) is the correct answer.

∆ G °

for this reaction is +422kJ. Therefore, thermodynamically reaction is not feasible.
We know that ,

∆ ° G = - n F E °

By using this equation value of

E °

can be calculated. Thus,

E ° = - \frac{∆ G °}{n F} = - 2.2 V

Therefore, for the occurrence of this reaction, external potential (emf) greater than 2.2V is required . Due to this fact (3) is not the correct option.

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