Question

Electrolysis of dilute and aqueous $NaCl$ is carried out using $Pt$ electrodes. As the electrolysis progresses:

• A. $pH$ increases
• B. $pH$ decreases
• C. $pH$ first decreases and then increases
• D. $pH$ remains constant

Answer 1

The correct option is D $pH$ remains constant

Electrolysis of dilute $NaCl\left(aq\right)$ carried out using inert electrodes:

Since ,
$E_{H_{2}O/H_2}^0>E_{N{a}^{+}/Na}^0$

Reaction at cathode:
$2H_{2}O\left(l\right)+2e^{-}\rightleftharpoons H_2\left(g\right)+2O{H}^{-}\left(aq\right)$

Reaction at anode: If concentration of $C{l}^{-}$ is low, oxidation of $H_{2}O$ to give $O_2$ is favoured.

$2H_{2}O\left(l\right)\rightleftharpoons 4H^{+}\left(aq\right)+O_2\left(g\right)+4e^{-}$

For the same number of electrons transferred, both $H^{+}$ and $O{H}^{-}$ ions produced, neutralise each other.
Hence $pH$ remains constant during electrolysis of dilute $NaCl\left(aq\right)$ using inert electrode.