H₂O₂ — Hydrogen Peroxide

Hydrogen Peroxide (H₂O₂) is one of the most important oxidizing agents used in industries and laboratories. It is a pale blue liquid in its pure form and is commonly available as an aqueous solution. The compound is widely used as a disinfectant, bleaching agent, and antiseptic. It was first discovered by Louis Jacques Thénard in 1818.

Hydrogen Peroxide exists as a weak acid in water and decomposes easily into water and oxygen. Its decomposition is accelerated by heat, light, or the presence of catalysts such as manganese dioxide (MnO₂), making it necessary to store it in dark-colored bottles.

The molecular structure of Hydrogen Peroxide can be represented as \(H_2O_2\), consisting of two oxygen atoms linked by a single bond and each oxygen atom bonded to a hydrogen atom. The molecule is non-planar and exhibits a dihedral angle (around 111°) between the two O–H bonds.

The bond between the two oxygen atoms (O–O) is relatively weak and responsible for its instability. The structure allows hydrogen bonding, which affects its physical properties like viscosity and boiling point.

Hydrogen Peroxide can be prepared both in the laboratory and industrially.

1. Laboratory Preparation:

It is prepared by the hydrolysis of barium peroxide (BaO₂) with dilute sulfuric acid:

The insoluble barium sulfate precipitates out, and hydrogen peroxide remains in the solution.

2. Industrial Preparation:

Industrially, it is manufactured by the auto-oxidation of anthraquinols. In this process, an anthraquinone is reduced to anthrahydroquinone, which reacts with oxygen to regenerate anthraquinone and produce hydrogen peroxide.

Physical Properties:

• Pale blue viscous liquid in pure form.
• Decomposes slowly to water and oxygen, especially under light or heat.
• Acts as a weak acid in aqueous solution.
• Forms hydrogen bonds similar to water, increasing its boiling point.

Chemical Properties:

• Decomposition: Hydrogen Peroxide decomposes into water and oxygen gas on heating or in the presence of catalysts:

• Oxidizing Nature: In acidic medium, H₂O₂ acts as an oxidizing agent:

• Reducing Nature: In alkaline medium, it acts as a reducing agent:

Hydrogen Peroxide has a wide range of applications in different sectors:

• Medical Use: Used as a mild antiseptic for cleaning wounds and cuts.
• Bleaching Agent: Commonly used in textile, paper, and hair bleaching industries.
• Water Treatment: Acts as a disinfectant and removes organic impurities.
• Environmental Use: Used in wastewater treatment as an eco-friendly oxidizer.
• Laboratory Use: Employed as an oxidizing agent in redox reactions.
• Rocket Propellant: Concentrated hydrogen peroxide serves as an oxidizer in some rocket engines.

Hydrogen Peroxide is unstable and decomposes upon exposure to heat, light, or metal ions. Therefore, it is stored in dark, airtight glass bottles with small amounts of stabilizers such as phosphoric acid. The decomposition reaction is represented as:

To prevent decomposition, it should be kept away from direct sunlight and metallic surfaces. Commercial solutions usually contain 3% to 6% H₂O₂ for domestic use, while industrial grades can reach up to 30% or more.

Hydrogen Peroxide is safe in low concentrations but can be corrosive at high concentrations. Direct contact with concentrated H₂O₂ can cause skin irritation and burns. Inhalation of vapors may lead to respiratory irritation. Always handle it with protective equipment.

Environmentally, hydrogen peroxide decomposes into harmless water and oxygen, making it an eco-friendly oxidizing agent compared to chlorine-based alternatives.