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Law of Equivalents

According to this law, the number of equivalents of the sub!>lance to be titrated is equal to the number of equivalents of the titrant used.

 

Derivation of the normality equation. Consider an acid alkali neutralization reactions. Let V 1 cm3 of an acid solution of N1 normality require V 2 cm3 of base of N2 normality.

We know that 1000 cm3 of 1 N acid solution contains acid = 1 gram equivalent.

V 1 cm3 of 1 N acid contains acid = 1 /1000 x V1 gram equivalents. Thus number of gram equivalents of acid in V1 equivalents of acid in V1cm3 of N1 acid solution  = V1 N1 / 1000

Similarly, number of gram equivalents of base in V 2 cm3 of its N2 solution = V2 N2 / 1000

By the law of equivalents, at the end point,

V1 N1 / 1000 = V2 N2 / 1000

N1 V1 = N2 V2