Explain chemical reduction and electrochemical reduction.

Reduction is the process in which metal oxides are converted into their respective metals.

There are 2 methods of reduction and they are:

i) Chemical reduction: This is the type of reduction in which metal oxide is heated with carbon or carbon monoxide to obtain the metal.

e.g. MnO₂(s) + 2C(s) → Mn(s) + 2CO(g)

Fe₂O₃(s) + 3CO (g) → 2Fe(s) + 3CO₂ (g)

Oxides of metals such as chromium, iron and manganese are heated with aluminium powder to obtain the metal.

e.g.

ii) Electrochemical reduction: All metals cannot be reduced by chemical method, some metals such as sodium, magnesium, etc cannot be reduced from carbon because of their more attraction towards oxygen. Hence, electrochemical reduction is used for the reduction of active metals.

In electrochemical reduction electrodes of inert metals like graphite or platinum are used in electrochemical cell.

e.g. electrochemical reduction of alumina to obtain aluminium.

Cathode: 2Al⁺³(l) +6e^-→ 2Al (l)

Anode: 3O^-2(l) → 3/2 O₂ (g) +6e^-