First slide

Electrolysis

Question

Aqueous solution of ${Na}_{2} {SO}_{4}$ is subjected to electrolysis using inert electrodes. Then the true statement is

Difficult

A

$p^{H}$ progressively increases
B

$p^{H}$ progressively decreases
C

$p^{H}$ remains unaltered
D

Cannot be predicted

Solution

$aq {Na}_{2} {SO}_{4}$ is a salt of SA – SB
$∴ p^{H} = 7$
Due to electrolysis:
At Cathode
Discharge potential of $H_{2} O$ is lesser than ${Na}^{+}$
$∴ 2 H_{2} O + 2 e^{-} \to H_{2} + 2 {OH}^{-}$
At Anode
Discharge potential of $H_{2} O$ is lesser than ${SO}_{^{4}}^{- 2}$
$2 H_{2} O \to 4 H^{+} + 4 e^{-} + O_{2}$
Left over solution is concentrated ${Na}_{2} {SO}_{4}$ . Composition doesn’t change but concentration increases. $p^{H}$ of a salt of SA-SB always is 7 irrespective of its concentration.

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