Introduction to preparation of hydrogen peroxide
LABORATORY PREPARATION OF HYDROGEN PEROXIDE
Hydrogen peroxide can be prepared in the laboratory by the action of ice cold, dilute sulphuric acid on sodium peroxide or hydrated barium peroxide BaO2. 8HO
Calculated quantity of sodium peroxide is added in small quantities to 20 % ice cold solution of sulphuric acid
Na2O2 (s) + H2SO4 Na2SO4 (s) + H2O2 (l)
Most of the sodium sulphate separates out on cooling as crystals of Na2SO4 . 10H2O, thus a 30 % of hydrogen peroxide containing small amount of sodium sulphate is obtained. Barium peroxide is made into a thin paste and added slowly to ice- cold dilute sulphuric acid.
BaO2 (s) + H2SO4 (aq) BaSO4 (s) + H2O2 (l)
Barium sulphate is allowed to settle down as a precipitate and filtered off. The filtrate obtained is a dilute solution of hydrogen peroxide. Phosphoric acid can be used in place of sulphuric acid . Alternatively , carbon dioxide gas may be passed through hydrated barium peroxide paste in ice cold water , in a slow stream.
2 BaO2 (s) + 2H3PO4 (aq) Ba( PO4) 2 (s) + 3H2O2 (l)
BaO2 (s) + CO2 + H2O2 BaCO3(s) + H2O2(l)
The precipitated Barium peroxide or Barium carbonate is filtered off which leaves Hydrogen peroxide.
MANUFACTURE OF HYDROGEN PEROXIDE BY ELECTROLYTIC PROCESS
Hydrogen peroxide is manufactured by electrolysis of 50 % sulphuric acid followed by vacuum distillation . The distillate is 30 % hydrogen [peroxide. The first product of electrolysis is peroxy disulphuric acid which is obtained by the electrolytic oxidation of sulphuric acid.
2H2SO4 `|->` 2H+ + 2HSO4-
2HSO4- `|->` H2S2O8 + 2e- ( at anode)
Peroxy- disulphuric acid H2S2O8 reacts with water during distillation to form hydrogen peroxide .
H2S2O8 (aq) + 2H2O (l) `|->` 2H2SO4 (aq) + H2O2 (aq)
2H+ + 2e- `|->` H2 (g) (at cathode)
Uses of Hydrogen Peroxide
H2O2 is a powerful but harmless disinfectant and germicide and used to clean wounds .
It is used as a bleaching agent for delicate textiles , wool , ivory , silk and wood pulp .
Highly concentrated solution of H2O is used as an oxidant for "Rocket Fuel" .
Hydrogen Peroxide solution is used to restore colour of 'oil paintings' which contain lead paints .
H2O2 is used as an oxidising agent in the laboratory .
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