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Assertion : Electrolysis of $\mathrm{NaCl}$ solution gives chlorine at anode instead of $\mathrm{O}_2$.
Reason : Formation of oxygen at anode requires over voltage.
Options:
Reason : Formation of oxygen at anode requires over voltage.
Solution:
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Verified Answer
The correct answer is:
If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
Electrolysis of $\mathrm{NaCl}$ is represented by following chemical reactions.
At cathode:
$$
\mathrm{H}^{+}(\mathrm{aq})+\mathrm{e}^{-} \longrightarrow \frac{1}{2} \mathrm{H}_2(\mathrm{~g})
$$
At anode:
$$
\begin{aligned}
&\mathrm{Cl}^{-}(\mathrm{aq}) \longrightarrow \frac{1}{2} \mathrm{Cl}_2+\mathrm{e}^{-} ; \mathrm{E}_{\text {cell }}^{\circ}=1.36 \mathrm{~V} \\
&2 \mathrm{H}_2 \mathrm{O}(\mathrm{aq}) \longrightarrow \mathrm{O}_2(\mathrm{~g})+4 \mathrm{H}^{+}(\mathrm{aq})+4 \mathrm{e}^{-} \\
&\mathrm{E}_{\text {cell }}^{\circ}=1.23 \mathrm{~V}
\end{aligned}
$$
$\mathrm{E}_{\text {cell }}^{\mathrm{o}}$ for this reaction has lower value but formation of oxygen at anode requires over potential.
At cathode:
$$
\mathrm{H}^{+}(\mathrm{aq})+\mathrm{e}^{-} \longrightarrow \frac{1}{2} \mathrm{H}_2(\mathrm{~g})
$$
At anode:
$$
\begin{aligned}
&\mathrm{Cl}^{-}(\mathrm{aq}) \longrightarrow \frac{1}{2} \mathrm{Cl}_2+\mathrm{e}^{-} ; \mathrm{E}_{\text {cell }}^{\circ}=1.36 \mathrm{~V} \\
&2 \mathrm{H}_2 \mathrm{O}(\mathrm{aq}) \longrightarrow \mathrm{O}_2(\mathrm{~g})+4 \mathrm{H}^{+}(\mathrm{aq})+4 \mathrm{e}^{-} \\
&\mathrm{E}_{\text {cell }}^{\circ}=1.23 \mathrm{~V}
\end{aligned}
$$
$\mathrm{E}_{\text {cell }}^{\mathrm{o}}$ for this reaction has lower value but formation of oxygen at anode requires over potential.
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