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Redox Reactions and Couple

In the electr...

Question

In the electrolysis of aqueous sodium chloride solution, which of the half cell reactions will occur at the anode?

N a_{(a q)}^{+} + e^{-} \to N a_{(s)}

E^{\circ} = - 2.71

volts

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2 H_{2} O_{(l)} \to O_{2} + 4 H^{+} + 4 e^{-}

E_{c e l l}^{\circ} = 1.23

volts

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H_{(a q)}^{+} + e^{-} \to \frac{1}{2} H_{2}

E_{c e l l}^{\circ} = 0.00

volts

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C l_{(a q)}^{-} \to \frac{1}{2} C l_{2} + e^{-}

E_{c e l l}^{\circ} = 1.36

volts

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Solution

The correct option is D $C l_{(a q)}^{-} \to \frac{1}{2} C l_{2} + e^{-}$
$E_{c e l l}^{\circ} = 1.36$ volts
During electrolysis of aqueous sodium chloride solution,
$N a C l ⟶ N a^{+} + C l^{-}$
$H_{2} O ⟶ H^{+} + O H^{-}$

$N a^{+} + e^{-} ⟶ N a ({E^{\circ}}_{c e l l} = - 2.71 V)$
$H_{(a q)}^{+} + e^{-} \to \frac{1}{2} H_{2} (E_{c e l l}^{\circ} = 0.00 V)$

At cathode:
$H_{2} O + e^{-} + ⟶ \frac{1}{2} H_{2} + O H^{-}$

(i)At anode:
$C l^{-} + \frac{1}{2} + e^{-} (E_{c e l l}^{\circ} = 1.36 V)$
$2 H_{2} O ⟶ O_{2} + 4 H^{+} + 4 e^{-} (E_{c e l l}^{\circ} = 1.23 V)$
(ii) The reaction at the anode with a lower value of $E^{\circ}$ should be preferred because oxidation of $O_{2}$ is kinetically a slow process and needs high voltage, thus reaction (i) takes place.

Suggest Corrections

Similar questions

N a^{+} (a q) + e^{-} \to N a (s) E^{0} = - 2.71 V

H^{+} (a q) + e^{-} \to \frac{1}{2} H_{2} (g) E^{0} = 0.00 V

(E^{0})

(a) Following reactions occur at cathode during the electrolysis of aqueous sodium chloride solution:

$N a^{+} (a q) + e^{-} \to N a (s) E^{\circ} = - 2.71 V$
$H^{+} (a q) + e^{-} \to \frac{1}{2} H_{2} (g) E^{\circ} = 0.00 V$

On the basis of their standard reduction electrode potential $(E^{\circ})$ values, which reaction is feasible at the cathode and why?

(b) Why does the cell potential of mercury cell remain constant throughout its life?

N a^{+} (a q) + e^{-} \to N a (s) E^{0} = - 2.71 V

H^{+} (a q) + e^{-} \to \frac{1}{2} H_{2} (g) E^{0} = 0.00 V

(E^{0})

{N a}^{+} (a q) + e^{-} ⟶ N a (s) E^{0} = - 2.71 V

H^{+} (a q) + e^{-} ⟶ \frac{1}{2} H_{2} (g) E^{0} = 0.00 V

(E^{0})

O_{2} (g)

⎡ ⎢ ⎢ ⎢ ⎢ ⎢ ⎣ \begin{matrix} (c o r r e c t) C u (s) ⟶ & C u^{2 +} (a q) + 2 e^{-} E_{C u | C u^{2 +}}^{⊝} = - 0.34 V (w r o n g) 2 H_{2} O (l) ⟶ & O_{2} (g) + 4 H^{\oplus} (a q) + 4 e^{-} E_{H_{2} O | O_{2}}^{⊝} = - 1.23 V \end{matrix} ⎤ ⎥ ⎥ ⎥ ⎥ ⎥ ⎦

\begin{matrix} I n (d) \end{matrix}

⎡ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎣ \begin{matrix} (c o r r e c t) N i (s) ⟶ & N i^{2 +} (a q) + 2 e^{-} E_{N i | N i^{2 +}}^{⊝} = - 0.25 V (w r o n g) 4 ⊝ O H (a q) ⟶ & O_{2} (g) + 2 H_{2} O (l) + 4 e^{-} E_{⊝ O H | O_{2}}^{\oplus} = - 0.4 V \end{matrix} ⎤ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎦

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