Calculating the concentration of hydrogen peroxide
71Hydrogen Peroxide was discovered by French Chemist J.L.Thenard in 1818. Large amounts of highly concentrated solutions of peroxide are required for commercial use. Hydrogen peroxide cannot be simply concentrated by distillation as it decomposes below its boiling point to water and oxygen. Hydrogen Peroxide is usually stored in wax coated plastic bottles which are dark in color. A stabilizer is usually added to it to prevent decomposition. Strength of hydrogen peroxide can be expressed as % strength or volume strength.
The most important use of hydrogen peroxide in daily life is in salons as a hair bleach and as a disinfectant. The hydrogen peroxide made availbale is a thick sryupy liquid. It decomposes in the presence of light and is therefore stored in opaque bottles. A stabilizer is usually added to prevent further decomposition. The strength of anaqueous solution of H2O2 can be expressed either as -
% strength- (w/v) It is the gms of H2O2 present in 100 mL of the solution
A 70%(w/v) soltion of H2O2 indicates 70 gms of H2O2 in 100 mL of solution
Volume Strength- In the market, this is the most commonly used method of expressing the strength of H2O2/ concentration. A solution labelled 30 volume means 1mL of the solution on heat decomposition is capable of releasing 30 mL of oxygen at NTP.
2H2O2--> 2H2O+O2
Therefore, according to the reaction 2X34 gms of H2O2 liberate 22.4 L of oxygen at NTP
Therefore, the gms of H2O2 that would liberate 30 L of oxygen gas for a 30 volume concentration can be calculated as follows-
30X2X34/22.4 = 91.07g
Thus, 1L of a 30 vol. concentration solution contains 91.07 g of H2O2
The strength of H2O2 in g/L can expressed as 91.07g/L
For thechemist, a cosmetologist as well as the manufacturer this information becomes an invaluable.
When concentration of H2O2 is to be expressed as Normality,
then the equivalent weight
of H2O2 is to be used. Normality= Strength/Eq.Wt
For a 30 volume strength, Normality = 91.07/17= 5.357N
