Question

A stock solution of 0.2 M Na2HPO4 is prepared by dissolving 28.4g of Na2HPO4 in one Litre of distilled water. Dissolve 21.016g of citric acid in 1 Litre of distilled water. How many gram Na2HPO4 is needed to make a stock solution of 250 ml? How many gram of citric acid is needed to make a stock solution of 250ml?

Answer 1

The Molarity of Na2HPO4 is 0.2 M

It is obtained by dissolving 28.4 g in 1L=1000 mL of water

                   by dissolving M g in 250 mL we get the required solution

M = ( 250x28.4) / 1000

   = 7.1 g

Therefore 7.1 g of Na2HPO4 is needed to make a stock solution of 250 ml

The stock solution of citric acid is prepared by

Dissolving 21.016g of citric acid in 1 Litre= 1000 mL of distilled water

Dissolving N g of citric acid in 250 mL of distilled water

N = (21.016 x 250)/1000

   = 5.254 g of citric acid

Therefore the mass of citric acid needed is 5.254 g