Hydrogen Peroxide - Structure, Preparation, and Properties of H2O2

What is Hydrogen Peroxide (H2O2)?

Hydrogen peroxide is the simplest kind of peroxide available (oxygen-oxygen single bond). It is a colorless liquid and is used in aqueous solution for safety reasons. It acts as a bleaching agent and is also used as a disinfectant. Concentrated hydrogen peroxide is a very reactive oxygen species and is used as a propellant in rocketry. The chemical formula for hydrogen peroxide is H2O2.

Table of Content

It is often referred to as water with one more oxygen atom. It is acidic in nature and PH is about 4.5. It is 100 percent degradable compound.

Hydrogen Peroxide

Overview of H2O– Hydrogen Peroxide

Hydrogen peroxide Chemical formula H2O2
Molecular Weight/ Molar Mass 4.0147 g/mol
Density 1.05 g/cm3
Boiling Point 150.2 °C
Melting Point -0.43 °C

Structure of Hydrogen Peroxide

The structure of hydrogen peroxide is non-planar. H2O2 has an open book structure with O – O spins. The dihedral angle is 111°. The O-O bond length is 145.8 pm and the O-H bond length is 98.8 pm(which is equal to 9.88 × 10-13 m). The following diagram will clearly show what an open book structure means.

Structure of Hydrogen Peroxide - Open Book Shape

Hydrogen Peroxide Structure

There are two planes in this structure and each plane has one O-H bond pair, the angle between both the planes is 90.2°.

⇒ Also Read: Chemical Bonding

Preparation of Hydrogen Peroxide

Let us have a look at the various methods of preparation for hydrogen peroxide.

Laboratory Methods of 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 Preparation

Hydrogen peroxide is prepared by the electrolysis of 30% ice-cold H2SO4. When acidified sulfate solution is electrolyzed at high current density, peroxodisulphate is obtained. Peroxodisulphate is then hydrolyzed to get hydrogen peroxide.

2HSO4(aq) [Electrolysis] → HO3SOOSO3H(aq) [Hydrolysis] → 2HSO4(aq)+2H+(aq)+H2O2(aq)

Reaction Mechanism

  • Electrolyte: 30% dilute H2SO4
  • Cathode: Pb wire
  • Anode: Pt rod

2H2SO4 → 2H+ 2HSO4

At Cathode: 2H+ 2e– → H2

At Anode: 

2HSO→ H2S2O+ 2e– ⇒ Peroxodi Sulphuric Acid [Marshall’s acid]

H2S2O+ H2O → H2SO+ H2SO⇒ Peroxomono Sulphuric Acid [Caro’s acid]

H2SO+ H2O → H2SO+ H2O2

Commercial Methods Of Preparation

Auto-Oxidation Method:

Preparation of Hydrogen Peroxide

Auto-Oxidation Method of Preparation of H2O2

Properties of Hydrogen Peroxide

Physical Properties:

  • In the pure state, hydrogen peroxide is 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.

Chemical Properties:

Hydrogen peroxide in both acidic and basic medium acts as an oxidizing as well as the reducing agent. The following reactions will give a clear picture:

Oxidation Reactions of H2O2

  • Oxidizes black Pbs to white PbSO4. Reaction: Pbs + 4H2O2 → PbSO+ 4H2O
  • Oxidises KI to Iodine. Reaction: 2KI + H2O→ 2KOH + I2
  • Oxidizes nitrites to nitrates. Reaction: NaNO+ H2O2 → NaNO3 + H2O
  • Oxidizes acidified Potassium ferrocyanide. Reaction: 2K4Fe(CN)6 + H2SO4 + H2O→ 2K3Fe(CN)6 + K2SO4 + 2H2O
  • Oxidizes sulphites to sulphates. Reaction: Na2SO3 + H2O2 → Na2SO4 + H2O
  • Oxidizes CrO-24 in an acid medium to chromium Peroxide CrO5Reaction: CrO-2+ 2H+ + 2H2O→ CrO5 + 3H2O

⇒ Check: Redox Reactions

Bleaching Reactions:

It bleaches by oxidation. H2O2 bleaches silk, wool, cotton, hair.

Reaction: H2O2 → H2O + [O] Nascent oxygen

Coloured substance + [O] → colourless

Reduction Reactions of Hydrogen Peroxide:

  • It reduces Barium Peroxide to monoxide. Reaction: BaO2 + H2O2 → BaO + H2O + O2
  • It reduces ozone to oxygen. Reaction: O+ H2O→ H2O + 2O2
  • It reduces alkaline potassium ferricyanide. Reaction: 2K3Fe(CN)+ 2KOH + H2O→ 2K4Fe(CN)+ 2H2O + O2

Why Hydrogen Peroxide is Stored in Plastic Containers?

Hydrogen peroxide decomposes when exposed to sunlight, this process is catalyzed by traces of alkali metals. Therefore, H2O2 is stored in wax-lined glass or plastic containers and kept in dark.

It should also be kept away from dust particles because dust can induce explosive decomposition of this compound.

How to Determine the Concentration of Hydrogen Peroxide?

Volume Strength of H2O2

10 Vol H2O2 means 1 mL of H2O2 gives 10 mL of O2 at STP.

Weight Percentage [w/w%]

Let us consider 10 Vol H2O2

2H2O→ 2H2O + O2

→ 68g of H2O2 gives 22.4 L of O2 at STP.

→ 10 L of O2 is given by

Amount of hydrogen peroxide = 10 × 68/22.4 = 30.36 g

1000 mL of H2O2 → 30.36 g

100 mL → ?

\(wt%=\frac{1\cancel{00}\times 30.36}{10\cancel{00}}\) = 30.36%

100 Vol H2O2 or 3.036%(w/w) H2O2 is known as Perhydrol.

Molarity of H2O2

To calculate the molarity, Let us consider 10 Vol H2O2

M = \(\frac{wt\times 1000}{GMw\times Vin\,\,mL}\)

Molarity of hydrogen peroxide = 30.36/34 = 0.89 M.

Normality of H2O2

Let us consider 10 Vol H2O2

N = \(\frac{wt\times 1000}{Gm.Eq.wt\times Vin\,mL}\)

= 30.36/17 = 1.78N

Uses of Hydrogen Peroxide

Since it acts as both an oxidizing as well as a reducing agent, it has a vast area of applications:

  • Hydrogen peroxide is used as an antiseptic.
  • It is used in the preservation of wine and milk.
  • Our white blood cells produce hydrogen peroxide to kill bacteria.
  • It is used to clean stains from sensitive fabrics and clothes.
  • Soaking feet in water mixed with H2O2 for 15 min every day for a week will help to get rid of fungus
  • Plant growth can be sustained by sprinkling mixture of hydrogen peroxide and water in equal amounts
  • The textile and paper industry use it as a bleaching agent.
  • It is used for the synthesis of tartaric acid, food products, and many pharmaceuticals.
  • It is used in the manufacture of chemicals which in turn are used in making of high-quality detergents.
  • The most significant use of H2O2 is in environmental chemistry where it is used in pollution control treatment of domestic waste and industrial effluents.
  • Highly concentrated Hydrogen Peroxide is used as rocket propellant.

Practise This Question

The frequency polygon below shows marks obtained by students of a class. 

From the graph, it can be said that the maximum number of student have scored ____