Hydrogen peroxide

Aug 26, 2022, 16:45 IST

About Hydrogen peroxide

Hydrogen peroxide was discovered by French chemist Thenard.

Preparation of Hydrogen peroxide

1. Laboratory method: In laboratory, is prepared by Merck’s process. It is prepared by adding calculated amounts of sodium peroxide to ice cold dilute (20%) solution of .

2. Industrial method : On a commercial scale, can be prepared by the electrolysis of 50% solution. In a cell, peroxy disulphuric acid is formed at the anode. This is drawn off from the cell and hydrolysed with water to give .The resulting solution is distilled under reduced pressure when gets distilled while with high boiling point, remains undistilled.

Physical properties of Hydrogen peroxide

1. Anhydrous is colourless, viscous liquid soluble in ether, alcohol and water. It gives blue tinge in thick layers

2. It causes blisters on skin and bitter in taste

3. Pure is weak acidic in nature and exist as associated liquid due to hydrogen bonding

4. Its specific gravity is 1.45 g/ml at 0.C

5. It is diamagnetic in nature

6. It boils at 1520C and freezes at . It begins to decompose at b.pt. and thus distilled under reduced pressure

7. In pure state, its dielectric constant is 93.7 which increases with dilution. Due to high dielectric constant, and its aqueous solution are good solvent.

Chemical properties of Hydrogen peroxide

(i) Decomposition : Pure is an unstable liquid and decomposes into water and either upon standing or upon heating,

(ii) Oxidising nature : is a powerful oxidant in acidic as well as in alkaline medium

Following are some important examples of oxidant action of Hydrogen peroxide

(a)oxidises black lead sulphide (PbS) to white lead sulphate (PbSO4)

(b)oxidizes sulphites into sulphates

(c)oxidizes nitrites to nitrates

(d). lilberates iodine from potassium iodide

(e). oxidizes arsenates into arsenates

(f). oxidizes acidified ferrous sulphate to ferric sulphate

(g). oxidizes into sulphur

(h). oxidizes acidified potassium ferrocyanide to potassium ferricyanide

(i). oxidizes formaldehyde to forinic acid in presence of pyrogallol and in alkaline medium

(j). dissolves the chromic hydroxide precipitate present in solution forming a yellow solution of sodium chromate

(k). oxidizes Benzene in presence of ferrous sulphate to phenol

(l).A solution of chromic acid in sulphuric acid or acidified potassium dichromate is oxidized to blue peroxide of chromium which is unstable, however, it is soluble in ether and produced blue coloured solution

Peroxide of chromium decomposes to form chromic sulphate & oxygen Peroxide of chromium is represented as (m) oxidizes mercury to mercuric oxide in acid solution

(iii) Bleaching action : acts as a bleaching agent due to the release of nascent oxygen. Thus, the bleaching action of is due to oxidation. It oxidises the colouring matter to a colourless product, Colouring matter +O Colour less matter

is used to bleach delicate materials like ivory, silk, wool, cotton, hair, leather etc.

(iv) Addition reactions: It shows addition reactions on ethylenic bond

Structure of Hydrogen peroxide

has non-planar structure in which two H-atoms are arranged in two directions almost perpendicular to each other and to the axis joining the two oxygen atoms. The O – O linkage is called peroxide linkage.

Strength of Hydrogen peroxide

The strength of is expressed in terms of weight or volume,

(i) As weight percentage : The weight percentage of gives the weight of in 100 g of solution. For example, a 40% solution by wt. means 40 g of are present in 100 g of solution.

(ii)As volume : The strength of is commonly expressed as volume. This refers to the volume of oxygen which a solution of will give. For example, a “20 volume” of means that 1 litre of this solution will give 20 litres of oxygen at NTP.