Ncert Exercises & Solutions

Given below are two statements:

Assertion (A):	Electrolysis of NaCl solution gives chlorine at anode instead of O₂ .
Reason (R):	Formation of oxygen at anode requires overvoltage.

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	(A) is false but (R) is true.

Hint: The overall reaction is as follows:

NaCl(aq) + H₂O(l) → Na⁺(aq) + OH^– (aq) +

\frac{1}{2}

H₂(g) +

\frac{1}{2}

Cl₂ (g)

Electrolysis of NaCl is represented by the following chemical reactions

At cathode

H^{+} (aq) + e^{-} ⟶ \frac{1}{2} H_{2} (g)

At anode

{Cl}^{-} (a q) \to \frac{1}{2} {Cl}_{2} + e^{-}; E °_{cell} = 1.36 V

2 H_{2} O (aq) ⟶ O_{2} (g) + 4 H^{+} (aq) + 4 e^{-}; E_{c e l l}^{°} = 1.23 V

E⁰_cell for this reaction has a lower value but the formation of oxygen at anode requires over potential.