Electrolysis using graphite electrodes

Question

which of the following substances, when carried out electrolysis usign graphite electrode, will give off gaseous products at both electrodes?

A Zinc sulphate solution
B Sodium bromide solution
C Molten sodium chloride
D Silver nitrate solution

With explanation ...
唔該

Answer 1

The answer is A.

A.
Anode : OH- ion is discharged preferentially because it is oxidized more readily than SO42- ion. Oxygen gas is given off.
4OH-(aq) → 2H2O(l) + O2(g) + 4e-
或 2H2O(l) → 4H+(aq) + O2(g) + 4e-
Cathode : H+ ion is discharged preferentially because it is reduced more readily than Zn2+ ion. Hydrogen gas is given off.
2H+(aq) + 2e- → H2(g)
或 2H2O(l) + 2e- → H2(g) + 2OH-(aq)

B is incorrect. Bromine formed at the anode is an aqueous solution, not a gas.
2Br-(aq) → Br2(aq) + 2e-

C. is incorrect. Sodium is formed at the cathode is a liquid, not a gas.
Na+(l) + e- → Na(l)

D is incorrect. Silver is formed at the cathode is a solid, not a gas.
Ag+(aq) + e- → Ag(s)

2007-04-13 17:51:49 補充：
C is not the answer.Molten sodium chloride is the liquid state of sodium chloride. It is obtained by heating sodium chloride solid to melt. It does NOTcontain water.It is the sodium chloride solution that gives hydrogen gas and chlorine gas to, but not molten sodium chloride.

2007-04-13 17:51:50 補充：
C is not the answer.Molten sodium chloride is the liquid state of sodium chloride. It is obtained by heating sodium chloride solid to melt. It does NOTcontain water.It is the sodium chloride solution that gives hydrogen gas and chlorine gas to, but not molten sodium chloride.

Answer 2

ans is not C
the NaCl is MOLTEN,no hydrogen and oxygen atoms present but only sodium and chlorine atoms,so electrolysis of this will only formNa on cathode and Cl2 at anode as u said

Answer 3

Ans : C

Becuase during eletrolysis process, the -ve electrode will attract the chloride elertron because of the concentration of chloride is higher than oxygen. And, at the +ve electrode will attract the Na+ to become sodium soild. But sodium will have a reaction with water to produce hydrogen gas.