3. Redox reaction
Reason —
Reaction at the cathode: Hydrogen ions, H+ being the only positively charged ions migrate to the cathode. Since the cathode is a reservoir of electrons, H+ ions gain an electron and become a neutral hydrogen atom. Therefore reduction takes place at the cathode.
H+ + e– ⟶ H
H + H ⟶ H2
Reaction at the anode: SO42- and OH– ions both migrate to the anode. OH–being lower in the electrochemical series is discharged preferentially.
OH– ions lose an electron to the anode and become neutral OH. The combination of OH forms water with the liberation of oxygen, giving off at the anode.
OH– ⟶ OH + e–
OH + OH ⟶ H2O + O
O + O ⟶ O2
Therefore, oxidation takes place at anode. Hence, electrolysis of acidified water is an example of redox reaction