Question

With reference to the electrolysis of acidulated water, answer the following:
(a) Why distill 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 the electrolysis of acidulated water considered as an example of catalysis?

Answer 1

(a) Distilled water is considered a non-electrolyte as there are no ions in it. It contains only molecules. As pure water lacks ions, it cannot be ionised and hence cannot conduct electricity.

(b) The electrolytic cell used in electolysis of acidulated water is called Hoffmann’s voltameter.

(c) The observations made during the electrolysis of water are:
(i)Cathode - Hydrogen gas is evolve
(ii)Anode - Oxygen gas is evolved.
The hydrogen and oxygen gases are collected in the ratio 2:1.

(d) The reaction at cathode: $4{\mathrm{H}}^{+}+4{\mathrm{e}}^{-}\to 2{\mathrm{H}}_2$ (Hydrogen gas)
The reaction at anode: ${\mathrm{4OH}}^{-}\stackrel{}{\to }{\mathrm{2H}}_2{\mathrm{O\; +\; O}}_2$ (Oxygen gas)
The complete cell reaction is: $2{\mathrm{H}}_2\mathrm{O}\stackrel{}{\to }2{\mathrm{H}}_2+{\mathrm{O}}_2$

(e) Electrolysis of acidulated water involves addition of sulphuric acid in order to form ions. The net change in the mass of sulphuric acid utilised in the electrolysis reaction is nil. Even though sulphuric acid is utilised in the reaction to produce ions, its mass remains unaltered at the end of the process, similar to a catalyst in a reaction. Thus, electrolysis of acidulated water is considered as an example of catalysis.