Hydrogen peroxide decomposes on heating as,

            
We know, 
     22400 mL of O₂ at STP are produced from H₂O₂ = 68 g

    10 ml of O₂ at STP would be produced from H₂O₂ = 
But 10 ml of oxygen at STP are produced from 1 ml of 10 volume of H₂O₂ solution.
Thus 1 ml of 10 volume at H₂O₂ solution contains  = 0.03036 g H₂O_2.

   1000 ml of 10 volume of H₂O₂ solution
would contain = 0 .03036 x 1000 = 30.36g H₂O₂
   Strength of 10 volume H₂O₂ = 30.36g L^-1

Strength of hydrogen peroxide:
(i) As percentage. It is expressed as W/V percentage of H₂O₂ in solution. Thus, 30% solution of H₂O₂ means 30 grams of H₂O₂ are present in 100 ml of solution.
(ii) In terms of volume. The strength of hydrogen peroxide is expressed in terms of volume i.e. the bottles containing hydrogen peroxide are generally marked as 10 volumes or 20 volumes or 30 volumes etc. A solution of hydrogen peroxide labelled as 20 volume actually means that 1 ml of hydrogen peroxide solution on decomposition by heat produces 20 ml of oxygen at NTP.
Let us now calculate the strength of 20 volume H₂O₂ in gram/litre.
Hydrogen peroxide decomposes on heating as:

(i) To calculate the mass of H₂O₂ in 1 litre of 2 M solution:
    Moleuclar mass of H₂O₂ = 2 x 1 + 2 x 16 = 34 amu
  Now 1 litre of 1 M solution contains
          H₂O₂ = 34 g



(ii) To calculate the volume of O₂ liberated at STP from 1000 cm³ of 2M solution:
             Decomposition of H₂O₂ can be represented as:
                      
                                
Now 68 g of  at S.T.P. given O₂ = 22400 cm³