Electrolysis

ELECTROLYSIS OR ELECTROLYTIC CONDUCTION:

Movement of the ions of an electrolyte to towards their respective electrodes and their deposition or liberation as neutral species under the influence of electric current is called electrolysis.

Electrolytic cell:

The cell used for the reaction to occur by passing electric current is called electrolytic cell. Thus electrolytic cell is a device which is used to convert electrical energy into chemical energy (a non-spontaneous chemical reaction takes place by the loss and gain of electrons).

For example: a device or electroplating or electrolysis of water in the presence of an acid. The process is called electrolysis or electrolytic conduction.

ELECTROLYSIS OF POTASSIUM CHLORIDE:

Potassium chloride (salt) does not conduct electricity in the solid state. To make it conduct electricity, either fuse or melt the salt or dissolve it in water. So there are two ways of doing electrolysis of potassium chloride. We are doing electrolysis of molten potassium chloride. Potassium chloride melts at 770$^0$C.

It is easy to predict the result of electrolyzing a molten electrolyte. The salt just splits into two parts. Potassium (metal) positive ion (K$^+$) and chloride (non-metal) negative ion (Cl$^-$).

KCl $\longrightarrow$   K$^+$ + Cl$^-$

At Cathode:

At cathode potassium ions gain electrons and do reduction to form potassium metal.

potassium ion + electron      potassium metal (Reduction)

2K$^+$     + 2e-    $\longrightarrow$        2 K

At Anode:

At anode chloride ions loose electrons and do oxidation to form chlorine atom. When Cl- ions arrive at anode, forming neutral chlorine (Cl) atoms but we know that Cl atoms do not exist in Free State. They combine to form Cl$_2$ molecules. So Cl- ions are discharged at anode to liberate Cl$_2$ gas by the loss of electrons at anode.

Chloride ion   Chlorine atom + e- (Oxidation)

Cl$^-$ $\longrightarrow$   Cl + e-

Cl$^-$ $\longrightarrow$   Cl + e-

Then            

    2Cl$^-$       $\longrightarrow$     Cl$_2$ +2e-

NET ELECTROLYSIS REACTION:

2K$^+$  +2e-    $\longrightarrow$        2 K

2Cl$^-$       $\longrightarrow$      Cl$_2$ +2e-

2K$^+$ + 2Cl$^-$    $\longrightarrow$    2K + Cl$_2$

The electrolysis of molten potassium chloride shows that we get potassium metal at cathode and Chlorine gas is liberated at anode.

Conclusion Thus electrolysis is a redox reaction. The reduction half-reaction occurs at the cathode, whereas the oxidation half-reaction occurs at the anode. The entire process, otherwise non-spontaneous, is driven by the electromotive force.