Hydrogen Peroxide

As you know that hydrogen does not exist in the free state in our environment. Instead due to its unique bonding nature, it forms various compounds. One such important compound is Hydrogen Peroxide. It has various applications and uses. Let us study.

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Hydrogen Peroxide

A peroxide is any compound which has two oxygen atoms bonded together. The O-O group is the peroxide group of the compound. And Hydrogen Peroxide is the simplest peroxide. The chemical formula for hydrogen peroxide is H2O2. It is a water molecule with one extra atom of oxygen, It has various uses ranging from disinfectant to propellant for rockets. Let us learn more about it

Browse more Topics Under Hydrogen

• Position of Hydrogen in the Periodic Table
• Hydrides
• Dihydrogen
• Preparation and Properties of Dihydrogen
• Water
• Heavy Water and Hydrogen Economy
• Hydrogen Peroxide

Properties of Hydrogen Peroxide

• Hydrogen Peroxide is an almost clear, pale blue liquid in its pure state
• It has an odour similar to that of nitric acid
• Hydrogen peroxide has a viscosity higher than water. It is about 40% denser than water
• The pure concentrated form boils around 150°C. However, at this temperature, it undergoes thermal decomposition and has an explosive reaction. This is why hydrogen peroxide is generally stored in an aqueous form. Also to avoid it reacting with the light we store it in dark color containers. It must be remembered that we have no practical knowledge of hydrogen peroxide’s boiling point. It is only a theoretical assumption. This is because it explodes before reaching its boiling point.
• It is miscible in water, i.e. it forms a homogeneous solution when mixed with water
• It is acidic in nature.
• H₂O₂ is a very strong oxidizing agent. It gives up one oxygen atom and forms water as a byproduct

PbS + 4H₂O₂ → PbSO₄ + 4H₂O (in acidic medium)

2Fe + H₂O₂ → 2Fe + 2OH (in basic medium)

• It can also act as a reducing agent if one of the reactants is a stronger oxidizing agent than hydrogen peroxide itself.

HOCl + H₂O₂ → H₃O + Cl + O₂ (in acidic medium)

I₂ + H₂O₂ + 2OH → 2I + 2H₂O + O₂

Volume Strength of Hydrogen Peroxide

Preparation of Hydrogen Peroxide

1] From Barium Peroxide

This is a method for laboratory preparation of Hydrogen Peroxide. Hydrated Barium Peroxide must be used, anhydrous barium peroxide will form a protective layer and not react with the sulphuric acid. The resulting H₂O₂ is a 5% concentrate solution.

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

2] From Sodium Peroxide

Here too we will use a dilute solution of Sulphuric Acid and gradually dissolve sodium peroxide in it. As you know H₂O₂ is explosive at high temperatures, so we use cold sulphuric acid. On reacting these two we get crystals of Sodium Sulphide and a 30% solution of hydrogen peroxide. We can perform vacuum distillation on the said solution to get pure hydrogen peroxide

Na₂O₂ + H₂SO₄ → Na₂SO₄ + H₂O_{2 (30%)}

Learn more about the Preparation of Dihydrogen here.

Structure of the Molecule

If you look at the dot diagram of H₂O₂ you will see the O-O bond. And you will see that both oxygen atoms have two pairs of unbound electrons each. This brings into effect the valence shell electron repulsion theory.

The hydrogen atoms will repel the unbonded electrons of oxygen. This gives a bent molecular shape. And it has a bod angel of 109.5° In its crystal form (solid state) this angel reduces due to hydrogen bonding within the molecules being formed.

Have a look at the unique position of Hydrogen in the Periodic Table.

Uses of Hydrogen Peroxide

Antiseptic

Hydrogen Peroxide has been used as an antiseptic for minor cuts, bruises, laceration etc for years. It actually foams when it comes in contact with blood. This helps in bringing up all the germs from within the cut. The oxidizing property of hydrogen peroxide kills the germs and also inhibits the growth of microorganisms such as bacteria, virus etc. This prevents the spread of any infection.

Concentrate H₂O₂ is harmful and dangerous so we use only a 3% dilute solution. Also, H₂O₂ is normally kept in dark brown bottles to avoid any decomposition in the light. Since it is explosive at higher temperatures, one must be careful in storing H₂O_2.

Bleaching

Hydrogen peroxide is extensively used for bleaching purposes. This also comes down to the oxidizing abilities of H₂O₂ . When a large organic molecule has a double bond this bond absorbs light.

During an oxidizing reaction when this bond breaks it destroys pigments and removes colour. Hydrogen peroxide is a good bleaching agent for hair since its byproducts (water and oxygen) are not harmful. H₂O₂ is also an excellent bleaching agent for wood, tarnish and paper and textiles.

Pollution Control Agent

Perhaps the most significant use of Hydrogen Peroxide is in environmental protection. It finds a use in air pollution control where it is used to treat effluents from industrial waste. It is also used in the restoration of aerobic conditions to sewage and industrial waste materials.

Read about Hydrides: Compounds that Hydrogen forms.

Solved Questions for You

Q: Last molecule of hydrogen is evolved from hydrogen peroxide by which of the following?

1. Crystallization
2. Evaporation
3. Oxidation
4. Distillation

Sol: The correct answer is “A”. The last molecule of water separates from H₂O by crystallization. 90% solution of hydrogen peroxide is concentrated by cooling with solid carbon dioxide and ether bath. The crystals of hydrogen peroxide are separated, melted and refrozen.