Question

A $20\%\left(w/w\right)$ aqueous salt solution contains $150\text{g}$ of water in it. How much water should be evaporated from it to make final concentration of $30\%\left(w/w\right)$?

• A. $66\text{g}$
• B. $62.5\text{g}$
• C. $68.7\text{g}$
• D. $61.4\text{g}$

Answer 1

The correct option is B $62.5\text{g}$

$20\%=\frac{x}{(150+x)}\times 100$
$\frac{1}{5}=\frac{x}{(150+x)}$
$x=37.5\text{g}$
Let the amount of water evaporated be $y\text{g}$
$\frac{37.5}{(150+37.5)-y}\times 100=30$
$\frac{37.5}{(187.5-y)}=\frac{3}{10}$
$y=62.5\text{g}$