Volumetric solution

Why is the preparation of 0.1 N perchloric acid VS . For molarity calculation factor is given as 0.20422 even though 1 ml is equivalent to 20.42 mg of 0.1 N perchloric acid, kindly clarify me.

204.22 is Formula weight of potassium bipthalate. potassium bipthalate is primary standard to determine normality of Perchloric acid.

1 ml of 0.1 N perchloric acid is equivalent to 20.42 mg of standard is the correct statement when we are calculating assay of a product by using this normal solution.

0.20422 is a factor used to determine normality/molarity of solution during standardisation

Molecular weight of PHP = 204.22 g/mol.
If you prepare 1M HClO4 the factor should be 0.20422 & for 0.1 N HClO4 it is also 0.20422.
The factor is determined by dividing MW by 1000 n it should be in Gram equivalent.

Then to determine the factor for 1M = (204.22 mg PHP
x 1 M/ 1000) = 0.20422.

That’s why for 0.1 M u need ( 0.1 x 204.22 mg) = 20.422 mg PHP.
Otherwise u can use factor (204.22 mg PHP
x 0.1 M/ 1000) = 0.020422 taking 204.22 mg PHP.

PHP = Potassium Hydrogen Phthalate