. From sodium peroxide (Merck’s method)

Calculated amount of sodium peroxide (Na2O2) is gradually added to an ice-cold solution of 20% H2SO4in small lots with constant stiring.

Na2O2+H2SO4→ Na2SO4+ H2O2

Upon cooling, crystals ofNa2SO4.10H2Oseparate out and the resulting solution contains about 30% H2O2. The solution also contains some dissolvedNa2SO4, but it does not interfere with the reactions ofH2O2. A pure sample ofH2O2may, however, be prepared by vacuum distillation.

2. From barium peroxide-Laboratory method of preparation.

Hydrogen peroxide is prepared from barium peroxide by the following methods:

(a)By the action of dilute sulphuric acid. Apaste of hydrated barium peroxide (BaO2.8H2O)is prepared in ice – cold water and then added slowly to an ice-cold solution of 20%H2SO4.

BaO2.8H2O+ H2SO4→ BaSO4+ H2O2+ 8H2O

The white precipitate of BaSO4is removed by filtration leaving behind a dilute solution (5%) of H2O2. In this method, anhydrous barium peroxide can not used since the precipitated BaSO4forms a protective layer around unreacted barium peroxide thereby preventing the further reaction