Question

A salt solution is prepared by dissolving 60 g of salt in 140 g of water. Calculate the amount of solute that should be added to make it ′s concentration 50% (w/w).

​

Answer 1

Let x g of solute that would be added to make its concentration 50% (w/W).

initial weight of solute = 60g

final weight of solute = (60 + x)g

final weight of solution = solute + solvent = (60 + x + 140) = (200 + x)g

now, percentage mass of solute = mass of solute/mass of solution × 100

or, 50 = (60 + x)/(200 + x) × 100

or, (200 + x) = 2(60 + x)

or, 200 + x = 120 + 2x

or, x = 80g

hence, 80g of solute should be added to make its concentration 50%