CE level Electrolysis

When a substance X is electrolysed using Pt electrodes, a gas is collected at each electrode. X may be:
A. silver nitrate solution
B. potassium chloride solution
C. molten sodium chloride
D. molten copper(II) chloride

A. false
The solution contains Ag^+, NO3^-, H^+ and OH^- ions.
Ag^+ and H^+ ions migrate to the cathode. Ag^+ ion is preferentially discharged to Ag metal because the concentration of Ag^+ ion is higher than that of H^+ ion. No gas is collected at the cathode.

B. true
The solution contains K^+, Cl^-, H^+ and OH^- ions.
K^+ and H^+ ions migrate to the cathode. H^+ ion is preferentially discharged to H2 gas because H^+ ion is reduced more readily than K^+. Hydrogen gas is collected at the cathode.
Cl^- and OH^- ions migrate to the anode. Cl^- ion is preferentially discharged to Cl2 gas because the concentration of Cl^- ion is higher than that of OH^- ion. Cl2 gas is collected at the cathode.

C. false
The molten liquid contains Na^+ and Cl^- ions.
Na^+ ion migrates to the cathode and is then discharged to Na metal. No gas is collected at the cathode.

D. false
The molten liquid contains Cu^+ and Cl^- ions.
Cu^2+ ion migrates to the cathode and is then discharged to Cu metal. No gas is collected at the cathode.


Electrolysis of 0.1M aq. solution of potassium iodide produce iodine?
or H2 at cathode, O2 at anode?

Iodine is produced.
The solution contains K^+, I^-, H^+ and OH^- ions. I^- and OH^- ions migrates to the anode. Although I^- is oxidized
slightly less readily than OH^- ion, I^‑ ion (0.1 M) is much more concentrated than OH^- ion (0.0000001 M at the beginning). Therefore I^- ion is preferentially discharged to I2.