Hydrogen Peroxide

Hydrogen peroxide is the other important hydride of oxygen. The oldest method of its preparation is by the action of dilute sulphuric acid on barium peroxide:

BaO₂ + H₂S0₄ ------------> BaSO₄, + H₂O₂

H₂0₂ when pure, is an almost colourless liquid, freezing at 272.1 K. k is less volatile 0.p. 423 K) than water and somewhat more dense and viscous. It is miscible with water in all proportions. The concentration of aqueous solutions of H₂0₂ is expressed in terms of volumes of o48en that will be liberated by a unit volume of H₂O₂ sample. The two largely used concentrations are 6 volumes and 30 volumes. Let us calculate the percentage of H₂O₂in a 6 volume sample.

2H₂O₂--------------->2H₂O + O₂

0.068kg----------------> 22.4dm³(at STP)

Since the strength of the sample is 6 volumes, 1 dm³ of H₂0₂ will produce 6 dm³ of 0, at STP. According to the above relationship 6 dm³ of O₂ would be produced by

0.068 x6/22.4 = 0.0182kg H₂O₂

Thus, I dm³ of a 6 volume sample of H₂0₂ will have 0.0182 kg of H₂Q₂. Hence, its concentration will be 0.0182 x 100 = 1.82 kg per 106 dm³ of sample = 1.82% w/v.

Pure liquid H₂0₂ is highly unstable. It decomposes easily; even a speck of dust can initiate explosive decomposition of concentrated solutions.

H₂0₂ can act both as an oxidising and a reducing agent. For example, it oxidises ferrous sulphate and lead sulphide to ferric sulphate and lead sulphate, respectively:

2FeSo₄ + H₂So₄ + H₂O₂-------->Fe₂ (SO₄)₃+ 2H₂O

Pbs + 4H₂O₂-----------> PbSO₄+ 4H₂O

It reduces chlorine to HCI as shown below:

Cl₂+ H₂o ------------------> HOCL +HCl

H₂O₂+ HOCL--------> HCl + H₂O + O₂

In industry, H₂O₂, is used mainly for bleaching cotton, wood pulp and other fibers. In the household it finds application as a mild antiseptic and as a bleaching agent.

The hydrogen peroxide molecule contains an 0-0 bond and has got a skewed configuration as shown fig.