Question

Calculate the mass of sodium sulphate required to prepare its 30percent mass present in 100 gram of water

Answer 1

Mass of the solution = mass of solute + mass of solvent

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 x grams.

Given that the mass of water is 100 g.

So,

20 = [x/(x + 100)] * 100

20/100 = [x/x + 100]

1/5 = x/x + 100

x + 100/5 = x

x + 100 = 5x

5x - x = 100

4x = 100

x = 100/4

x = 25

Thus, 25g of sodium sulphate is required.

Answer 2

Let the mass required to do so be x
then,

$\frac{x}{x + 100} \times 100= 30 \\ \frac{x}{x + 100} = \frac{30}{100} \\ 100x = 30(x + 100) \\ 100x = 30x + 3000 \\ 100x - 30x = 3000 \\ 70x = 3000 \\ x = \frac{3000}{70} \\ x = \frac{300}{7} \\ x = 42.857142857142...$

Mass of sodium sulphate will be ≈ 42.8 grams.