Hydrogen peroxide preparation by electrolytic method

Hydrogen peroxide is largely manufactured by the electrolysis of 50% Sulphuric acid at 0^{\circ} \textrm{} C between platinum anode and lead cathode separated by a porous diaphragm.

50% Sulphuric acid solution is taken in a stoneware vessel. A platinum rod is dipped in the solution which acts as anode. A lead wire acts as the cathode. These two electrodes are separated of a porous diaphragm.

The vessel is placed in a trough of ice to maintain the temperature at 0^{\circ} \textrm{} C.

On passing current the following reactions takes place.

2\textrm{} H_{2} \textrm{} S \textrm{} O_{4} \rightleftharpoons  2 \textrm{} H^{+} + 2 \textrm{} H \textrm{} S \textrm{} O_{4}^{-} (Ionization)

Oxidizing properties :

\textrm{} H_{2}\textrm{} O_{2} decomposes as \textrm{} H_{2}\textrm{} O_{2} \longrightarrow \textrm{} H_{2} \textrm{} O + [O]. Because of this tendency, it acts as powerful oxidant.

Examples:

It oxidizes black lead sulphide to white lead sulphate.

\textrm{} p\textrm{} b \textrm{} S + 4 \textrm{} H_{2} \textrm{} O_{2} \longrightarrow \textrm{} p \textrm{} b \textrm{} S \textrm{} O_{4} + 4 \textrm{} H_{2} \textrm{} O

It oxidizes potassium iodide to iodine in presence of sulphuric acid.

2 \textrm{} K \textrm{} I + \textrm{} H_{2} \textrm{} O_{2} + \textrm{} H_{2} \textrm{} S \textrm{} O_{4} \longrightarrow \textrm{} K_{2} \textrm{} S \textrm{} O_{4} + \textrm{} I_{2} + 2 \textrm{} H_{2} \textrm{} O

It oxidizes ferrous sulphate to ferric sulphate in presence of sulphuric acid.

2 \textrm{} F \textrm{} e \textrm{} S \textrm{} O_{4} + \textrm{} H_{2} \textrm{} S \textrm{} O_{4} + \textrm{} H_{2} \textrm{} O_{2} \longrightarrow \textrm{} F \textrm{} e_{2}\left ( \textrm{} S \textrm{} O_{4} \right )_{3} + 2 \textrm{} H_{2} \textrm{} O

Reducing Properties :

\textrm{} H_{2}\textrm{} O_{2} acts as a reducing agent because of the ease with which it accepts nascent oxygen from other oxidising agent.

\mathrm{} H_{2} \mathrm{} O_{2} + (\mathrm{} O) \longrightarrow \mathrm{} H_{2} \mathrm{} O + \mathrm{} O_{2}

It reduces moist silver oxide to metallic silver.

\textrm{} A \textrm{} g_{2} \textrm{} O + \textrm{} H_{2} \textrm{} O_{2} \longrightarrow 2 \textrm{} A \textrm{} g + \textrm{} H_{2} \textrm{} O + \textrm{} O_{2}

It reduces ozone to oxygen.

\textrm{} H_{2} \textrm{} O_{2}+ \textrm{} O_{3} \longrightarrow \textrm{} H_{2} \textrm{} O +2 \textrm{} O_{2}

It decolourises acidified potassium permanganate solution.

Hydrogen peroxide preparation by electrolytic method.