Question

Calculate the mass of sodium sulphate required to prepare 20% solution in hundred grams of water

Answer 1

Na2so4 = 142 g/mol

now 100 g implies 20 g sol required
so 142 g implies how many

answer is 142*20/100

Answer 2

The mass by mass percentage of a solution is given by the following relation
mass by mass percentage = (mass of solute / mass of solution) X 100
where
mass of the solution = mass of solute + mass of solvent
Here we are given that the mass percent of sodium sulphate solution is 20 %. Let the mass of sodium sulphate which is required to prepare this solution be 'a' grams. We are given that the mass of water is 100 g. So
20 = [a / (a + 100)] X 100
Solving for a, we get
a = 25g
Thus, 25g of sodium sulphate is required