Question

Calculate the mass of sodium sulphate required to prepare its $20\%$ (mass percent) solution in $100g$ of water.

Answer 1

Let the mass of sodium sulphate required be = $xg$.
The mass of solution =$(x+100)g$
$xg$ of solute in $(x+100)g$ of solution
$20\%=\frac{x}{x+100}\times 100$
$20x+2000=100x$
$80x=2000$
$x=\frac{2000}{80}$ or $x=25g$
$25g$ of sodium sulphate will be required to prepare its $20\%$ solution in $100g$ of water.