Question

In the electrolysis of acidulated water, ${SO}_4^{-2}$ ions do not get discharged at anode. Identify the correct reason.

• A. ${SO}_4^{2-}$ ions have lower discharge potential
• B. ${SO}_4^{2-}$ ions have higher discharge potential
• C. The concentration of ${SO}_4^{2-}$ ions is very less in the electrolyte
• D. ${SO}_4^{2-}$ ions get neutralized by $H^{+}$ ions

Answer 1

The correct option is B ${SO}_4^{2-}$ ions have higher discharge potential

There is competition between the negative ions $O{H}^{-}$ and $S{O}_4^{2-}$ at the positive anode. The sulphate ions compete with the hydroxide ions to release their electrons to the anode.$S{O}_4^{2-}$ ions have higher discharge potential. The hydroxide ions are much better reducing agents and are preferentially released as oxygen gas and water.
$4O{H}^{-}+4e^{-}\to 2H_{2}O+O_2$