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