What is the mass of sodium sulphate required to prepare its 20% (mass per cent) solution in 100g of water?

Given,
- Mass percent (mass %) = 20%

- Mass of water = 100g

- Mass percent formula:

Mass % = (Mass of solute / Mass of solution) × 100

Mass of solution = Mass of solute + Mass of water

Let the mass of sodium sulphate be x.

x / (x + 100) × 100 = 20

x = 0.2 × (x + 100)

x = 0.2x + 20

0.8x = 20

x = 20 / 0.8 = 25

Correct Answer: 25g