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2 Electrolysis of aqueous salt solutions

If two or more ions of the same kind emerge, which often occurs in aqueous

solutions, the sequence of electrode processes should be known.

9.4 Cathode processes

It is obvious that during the electrolysis the cations, the discharging

potential of which is the least negative (most positive), are discharged first of all.

During the passage of electric current through aqueous solutions of active metals

salts, placed in the range of electrochemical potentials up to aluminum inclusive,

the cathode will not restore the metal ions, and the water molecules and the

cathode process will be as follows:

–
2H 2O + 2 ē = H 2 + 2OH ,

+
2H 3O + 2 ē = H 2 + 2H 2O.

During the electrolysis of salts of medium activity metals there are two
processes on a cathode: both metal ions and water molecules will be restored. The

cathodic process will be as follows:
2+
Zn + 2 ē = Zn,

–
2H 2O + 2 ē = H 2 + 2OH .

During the electrolysis of passive metals salts only metal ions will be

restored on the cathode:

2+
Cu + 2 ē = Cu.

9.5 Anode processes

The sequence of discharging anions can be approximately expressed by the

rule: at first anions of nonoxygen-containing acids discharge, and then water

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