Periodic Table of Elements
1

Hydrogen

1.008

Hydrogen Peroxide H2O2

Hydrogen Peroxide was discovered by French Chemist J.L.Thenard in 1818.

Physical and chemical properties

  • Physical State: liquid
  • Appearance: clear, colorless
  • Odor: slight pungent odor
  • Molecular Formula: H2O2
  • Molecular Weight: 34.0128
  • pH:n3.3 (30% solution), 1.3 (70% solution)
  • Vapor Pressure: 23 mm Hg @ 30°C
  • Vapor Density: 1.10
  • Evaporation Rate: >1.0 (Butyl acetate=1)
  • Viscosity: 1.25 cP
  • Boiling Point: 108°C (226°F) @ 1.013 bar (760 mmHg) for 35% hydrogen peroxide, 115°C (239°F) @ 1.013 bar (760 mmHg) for 50% hydrogen peroxide
  • Freezing/Melting Point: 33°C (27°F) for 35% hydrogen peroxide, 52°C (62°F) for 50% hydrogen peroxide
  • Autoignition Temperature: Non combustible
  • NFPA Rating: (estimated) Health: 3; Flammability: 0; Reactivity: 1
  • Solubility: Miscible in water in all proportions and forms hydrate H2O2.H2O.
  • Specific Gravity/Density: 1.1-1.2 (30-50%)
  • Flash Point: Non Flammable
  • Stability: It decomposes slowly to release oxygen. Unstable when heated or contaminated with heavy metals, reducing agents, rust, dirt or organic materials. Stability is reduced when pH is above 4.0.
  • Decomposition : Pure H2O2 is an unstable liquid and decomposes into water and O2 either upon standing or upon heating.

    • H2O2 H2O + O2

  • Oxidising properties:

    • Hydrogen peroxide is a powerful oxidising agent. It acts as an oxidising agent in neutral, acidic or in alkaline medium.

    PbS + 4H2O2 PbSO4 + 4H2O (in neutral solution)
    FeSO4 + H2SO4 + H2O2 Fe2SO43 + 2H2O (in acidic solution)
    MnSO4 + H2O2 + 2NaOH MnO2 + Na2SO4 + 2H2O (in alkaline solution)

  • Reducing properties:

    • Hydrogen peroxide acts as an reducing agent in neutral, acidic or in alkaline medium.

    Ag4O + H2O2 2Ag + 2H2O + O2

  • Bleaching properties:

    • Hydrogen peroxide acts as bleaching agent. The bleaching action of H2O2 is due to oxidation.

    H2O2 H2O + O2

  • Acidic properties:

    • Hydrogen peroxide is acidic in nature. It reacts with alkalies and decomposes carbonates. Its dissociation constant Ka is 1.55 × 10–12 at 298 K.

    H2O2 + 2NaOH Na22 + 2H2O

Preparation of hydrogen peroxide

Hydrogen peroxide can be prepared by any one of the following methods:

1. From Barium peroxide:

Action of sulphuric acid or phosphoric acid on hydrated barium peroxide BaO2.8H2O produces hydrogen peroxide.

BaO2.8H2O + H2SO4 BaSO4 + H2O2 + 8H2O

2. By electrolysis of 50% H2SO4

H2O2 can be prepared by the electrolysis of 50% H2SO4 solution. 50% H2SO4 solution on electrolysis produces peroxydisulphuric acid H2S2O8 (Marshall's acid) at the anode. Peroxy disulphuric acid on hydrolysis with water produces H2O2. H2O2 distills first leaving behind the H2SO4 which is recycled.

2H+ + 2e- H2O At cathode
2HSO4- H2S2O8 + 2e- At anode
H2S2O8 + 2H2O H2O2 + H2SO4

3. By auto oxidation of 2-ethylanthraquinol

The H2O2 obtained by this method is further concentrated by distillation under reduced pressure.

2-ethylanthraquinol 2-ethylanthraquinone + H2O2

4. Merck’s process

In this process H2O2 is prepared by adding calculated amounts of sodium peroxide to ice cold dilute (20%) solution of H2SO4.

Na2O2 + H2SO4 Na2SO4 + H2O2

Uses of hydrogen peroxide

  • Hydrogen peroxide is most commonly used as a bleaching agent.
  • Small amounts of hydrogen peroxide are also added to some toothpastes as whitening agents.
  • Hydrogen peroxide is also used to prevent infections in cuts.
  • As an antiseptic, it is sold in the market as perhydrol.
  • It is used as mild bleach in laundry detergents.
  • It is used foror bleaching silk, wool, hair and leather.
  • Industrially, the largest use is for pulp and paper-bleaching.
  • It is also used in chemical synthesis, steel production, and wastewater treatment.
  • It can be used either as a monopropellant (not mixed with fuel) or as the oxidizer component of a bipropellant rocket.