Question

When $400$ g of a $20\%$ solution by mass was cooled, $50$ g of solute precipitated. The percentage (by mass) concentration of the remaining solution is (as the nearest integer) :

Answer 1

Mass of solution $=$ $400$ g
Mass of solute $=\frac{20\times 400}{100}=80$ g
Mass of solute precipitated $=$ $50$ g
Mass of solute remained in solution $=80-50=30$ g
And, mass of solution remained $=$ $400-50$ $=$ $350$ g
$\%$ (by mass) concentration $=\frac{30}{350}\times 100=8.57\%$
So, answer is $9$.