Friday, September 20, 2013

Hydrogen peroxide ( Laboratory Preparation )

  • Hydrogen peroxide was first discovered by Thenard in 1818.
  • Hydrogen peroxide is a clear liquid.
  • Hydrogen peroxide is slightly more viscous than water.
  • It is a strong oxidizer. 
  • In dilute solution it appears colorless.
  • It is used as a bleach or cleaning agent.
  • Traces of hydrogen peroxide are found in atmosphere and in certain plants.
Laboratory Preparation of Hydrogen peroxide: 
             Hydrogen peroxide is prepared by Merck's process. In this method calculated quantities of sodium peroxide to ice cold dilute 20% solution of sulphuric acid. 30% of hydrogen peroxide is obtained by this process.
                        Na2O2     +     H2SO4     →     Na2SO4      +     H2O2
Pure hydrogen peroxide is obtained by reacting BaO2   with an acid.
                        BaO2      +      H2SO4      →     BaSO4         +      H2O2
                      3BaO2      +      2H3PO4     →    Ba3(PO)4      +     3H2O2
Phosphoric acid is preferred to  H2SO4  because soluble impurities like Barium persulphate tends to decompose  H2O2 while  H3PO4  is act as preservative ( negative catalyst ) for hydrogen peroxide. 
Hydrogen peroxide is manufactured by the electrolysis of 50% sulphuric acid followed by vacuum distillation. Here 30% of pure hydrogen peroxide is obtained.