Hydrogen peroxide is largely manufactured by the electrolysis of 50% Sulphuric acid at
Laboratory Methods of Hydrogen Peroxide Preparation
When barium peroxide is acidified and the excess water is removed by the process of evaporation under reduced pressure, we obtain hydrogen peroxide. The following reaction will clarify this:
BaO2.8H2O(s) + H2SO4(aq) → BaSO4(s) + H2O2(aq) + 8H2O(l)
Industrial Method of Hydrogen Peroxide Preparation
Hydrogen peroxide is prepared by the electrolysis of 30% ice-cold H2SO4. When acidified sulfate solution is electrolyzed at a high current density, peroxodisulphate is obtained. Peroxodisulphate is then hydrolyzed to get hydrogen peroxide.
2HSO–4(aq) [Electrolysis] → HO3SOOSO3H(aq) [Hydrolysis] → 2HSO–4(aq)+2H+(aq)+H2O2(aq)
- Electrolyte: 30% dilute H2SO4
- Cathode: Pb wire
- Anode: Pt rod
2H2SO4 → 2H+ + 2HSO–4
At Cathode: 2H+ + 2e– → H2
2HSO–4 → H2S2O8 + 2e– ⇒ Peroxodi Sulphuric Acid [Marshall’s acid]
H2S2O8 + H2O → H2SO5 + H2SO4 ⇒ Peroxomono Sulphuric Acid [Caro’s acid]
H2SO5 + H2O → H2SO4 + H2O2
Properties of Hydrogen Peroxide
- In its pure state, hydrogen peroxide is an almost colorless (very pale blue) liquid.
- It melts at 272.4 K and has a boiling point of 423 K (extrapolated).
- It is miscible in water in all proportions and forms hydrates.
Hydrogen peroxide in both acidic and basic mediums acts as an oxidizing as well as a reducing agent. The following reactions will give a clear picture:
Oxidation Reactions of H2O2
- Oxidizes black Pbs to white PbSO4. Reaction: Pbs + 4H2O2 → PbSO4 + 4H2O
- Oxidises KI to Iodine. Reaction: 2KI + H2O2 → 2KOH + I2
- Oxidizes nitrites to nitrates. Reaction: NaNO2 + H2O2 → NaNO3 + H2O
- Oxidizes acidified Potassium ferrocyanide. Reaction: 2K4Fe(CN)6 + H2SO4 + H2O2 → 2K3Fe(CN)6 + K2SO4 + 2H2O