Hydrogen Peroxide (H2O2) is a chemical compound made up of two hydrogen atoms and two oxygen atoms. It is a pale blue liquid at room temperature and is used as a disinfectant and bleaching agent.

Hydrogen peroxide, with the chemical formula H2O2, is the simplest kind of peroxide available, consisting of an oxygen-oxygen single bond. It is a colourless liquid and is often used in aqueous solution for safety purposes, such as a bleaching agent and a disinfectant. Concentrated hydrogen peroxide is a highly reactive oxygen species and is used as a propellant in rocketry.

Table of Contents

Overview of Hydrogen Peroxide

Structure of Hydrogen Peroxide

Preparation of Hydrogen Peroxide

Properties of Hydrogen Peroxide

Concentration of Hydrogen Peroxide

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

Hydrogen Peroxide

Overview of H2O2 - 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 at a dihedral angle of 111°. The O-O bond length is 145.8 pm (equal to 14.58 × 10-12 m) and the O-H bond length is 98.8 pm (equal to 9.88 × 10-13 m). The following diagram illustrates an open book structure:

Hydrogen Peroxide Structure

There are two planes in this structure, each containing one O-H bond pair. The angle between the two planes is 90.2°.

⇒ Learn More About Chemical Bonding Here

Preparation of Hydrogen Peroxide

Let’s Take a Look at the Different Ways to Prepare 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 Preparation Methods

The electrolysis of 30% ice-cold H2SO4 produces peroxodisulphate, which is then hydrolyzed to yield hydrogen peroxide.

2HSO${4}$(aq) [Electrolysis] $\rightarrow$ HO${3}$SOOSO${3}$H(aq) [Hydrolysis] $\rightarrow$ 2HSO${4}$(aq) + 2H$^{+}$(aq) + H${2}$O${2}$(aq)

Reaction Mechanism

Electrolyte: 30% Dilute H2SO4

Cathode: Pb (Lead) wire

Anode: Pt rod

2H_2SO_4 \rightarrow 2H^+ + 2HSO_4^-

At Cathode: 2H⁺ + 2e^- → H₂

At Anode:
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2H_2SO_4 + 4e^- → H_2S_2O_8 + 2e^- ⇒ Peroxodisulfuric Acid [Marshall’s Acid]

H$_2$S$_2$O$_8$ + H$_2$O $\rightarrow$ H$_2$SO$_5$ + H$_2$SO$_4$ $\Rightarrow$ Peroxomono Sulphuric Acid [Caro’s Acid]

H2SO5 + H2O → H2SO4 + H2O2

Commercial Methods of Preparation

Auto-Oxidation Method:

Auto-Oxidation Method of Preparation of H2O2

Properties of Hydrogen Peroxide

Physical Properties:

In its pure state, hydrogen peroxide is a nearly colorless (very pale blue) liquid.

It melts at -0.85°C and has a boiling point of 149.85°C (extrapolated).

It is miscible in water in all proportions and forms hydrated compounds.

Physical Properties:

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

Oxidation Reactions of H2O2

Reaction: Pb + 4H2O2 → PbSO4 + 4H2O

Reaction: 2KI + H2O2 → 2KOH + I2

Reaction: NaNO2 + H2O2 → NaNO3 + H2O

Statement: Nitrites are oxidized to nitrates.

Reaction: 2K4Fe(CN)6 + H2SO4 + H2O₂ → 2K₃Fe(CN)₆ + K₂SO₄ + 2H₂O

Reaction:

* Oxidizes sulphites to sulphates.
Reaction: Na2SO3 + H2O2 → Na2SO4 + H2O

Reaction: CrO-24 + 2H+ + 2H₂O₂ → CrO₅ + 3H₂O

⇒ Check Redox Reactions here

Bleaching Reactions:

H2O2 bleaches silk, wool, cotton, and hair through oxidation.

Reaction: 2H2O2 → 2H2O + [O] Nascent oxygen

Coloured substance + [O₂] → colourless

Reduction Reactions of Hydrogen Peroxide:

Reaction: BaO2 + H2O2 → BaO + H2O + O2

Reaction: O3 + H2O2 → H2O + 2O2

2K3Fe(CN)6 + 2KOH + H2O2 --> 2K4Fe(CN)6 + 2H2O + O2

Reaction: 2K3Fe(CN)6 + 2KOH + H2O2 --> 2K4Fe(CN)6 + 2H2O + O2

How Does Storing Hydrogen Peroxide in Plastic Containers Help?

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

It should also be kept away from dust particles, as dust can cause the explosive decomposition of this compound.

Determining the Concentration of Hydrogen Peroxide

Strength of H2O2 Volume

1 mL of H2O2 yields 10 mL of O2 at STP when reacted.

Weight Percentage (w/w%)

Let us consider 10 mL of H2O2

2H_2O_2 \rightarrow 2H_2O + O_2

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

→ 10 L of O₂ is given

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

30.36 g of H2O2 is equal to 1000 mL

100 mL → 100 mL

‘(\begin{array}{l}wt%=\frac{30.36}{10}\end{array} )’

30.36%

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

Molarity of H₂O₂

To calculate the molarity, let us consider 10 Vol H2O2 (Molarity Formula).

(\begin{array}{l}M = \frac{wt \times 1000}{GMw \times V_{in} \ \ mL}\end{array})

Molarity of hydrogen peroxide = 0.89 M.

Normality of Hydrogen Peroxide (H2O2)

Let us consider 10 mL of H2O2

(\begin{array}{l}N = \frac{wt \times 1000}{Gm.Eq.wt \times V_{in} \ mL}\end{array})

1.78N = 30.36/17

Learn More: What is Hydrogen Peroxide Used For

Hydrogen Peroxide - Video Lesson

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Frequently Asked Questions (FAQs)

What are the uses of hydrogen peroxide?

• Hydrogen peroxide is a colourless liquid, it is a strong oxidizing agent, and it has a boiling point of 150.2°C.

The physical properties of hydrogen peroxide are:

It is a pale blue color in its pure form.

The viscosity of H2O2 is slightly greater than that of water.

The boiling point of hydrogen peroxide is 150.2°C.### What is the oxidation state of oxygen in hydrogen peroxide?

The oxidation state of oxygen in hydrogen peroxide is -1. An example of a reaction in which hydrogen peroxide is an oxidizing agent is the decomposition of hydrogen peroxide to water and oxygen:

$$2H_2O_2 \rightarrow 2H_2O + O_2$$

Sodium nitrate is oxidized to sodium nitrite by hydrogen peroxide.

O3 + H2O2 → O2 + H2O

Ozone reacts with hydrogen peroxide to produce oxygen and water. In this reaction, hydrogen peroxide acts as a reducing agent.

O3 + H2O2 → H2O + 2O2