Question

With reference to the electrolysis of acidulated water, answer the following :
a) why distilled water is a non- electrolyte?
b) What is the electrolytic cell called?
c) State what you would observe at the (i) Cathode (ii) Anode
d) Summarize the electrode reactions.
e) why is electrolysis of acidulated water considered as an example of catalysis?

Answer 1

a) Distilled water is a non electrolyte because it does not contain any ions.
b) The electrolytic cell used in electrolysis of acidulated water is called Hoffmann's Apparatus.
c) (i) At Cathode : Hydrogen ions are H⁺ ions. They migrate to the cathode and discharge there. The ions gain electrons from the cathode to form atoms of Hydrogen which combine in pairs to form molecules of Hydrogen.
H⁺ + e^- → H

H + H → H₂ or 
4H⁺ + 4e^- → 2H₂
(ii) At anode : Sulphate ions and hydroxyl ions are the anions present in the solution. Both migrate to the anode. OH^- ions are discharged in preference to sulphate ions. The OH^- ions loose their elctrons and become elcctrically neutral particles of OH, which react among themselves to give water and oxygen.
2OH^- - 2e^- → H₂O + O
Or 4OH^- - 4e^- → 4OH
4OH → 2H₂O + O₂
d) Electrolytic Cell : Hoffmann Voltameter
Electrolyte : Acidified water
Electrode : Cathode - Platinum Foil, Anode - Platinum Foil
Dissociaton of acidified water :
\[\ce{H2SO4 ⇌ 2H+ + SO^{-2}_{4}}\]

\[\ce{H2O ⇌ H+ + OH-}\]

Reaction at cathode :
H⁺ + e^- → H
H + H → H₂
Or 4H⁺ + 4e^-  → 2H₂
Reaction at anode :
20H^- - 2e^-→ H₂O + O
Or 40H^- - 4e^- → 4OH
4OH → 2H₂O + O₂

e) Electrolysis of acidulated water is considered as an example of catalysis because the reaction is catalyzed by acids.