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  H₂O_{2 while}  H₃PO_{4  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.