Question

In what mass of water must $25g$ of $CuS{O}_4.5H_{2}O$ be dissolved to obtain an $8\%$ solution of $CuS{O}_4$ ? $\left(At.wt.ofCu=63.5\right)$
Round off answer to the nearest integer value.

Answer 1

Answer: 175

$25gofCuS{O}_4.5H_{2}O$
$\because 249.5gofCuS{O}_4.5H_{2}O$ contain $159.5gofCuS{O}_4$
$\therefore 1g\text{of}CuS{O}_4.5H_{2}O\text{contains}\frac{159.5}{249.5}g\text{of}CuS{O}_4$
$\therefore 25g\text{of}CuS{O}_4.5H_{2}O\text{contains}\frac{159.5}{249.5}\times 25=15.98g\text{of}CuS{O}_4$
For $8\%$ solution, Let $x$ is the weight of solution
$\therefore x\times \frac{8}{100}=15.98$
$x=\frac{1598}{8}=199.75g$
$\therefore$ Weight of water $=199.75-25=174.75g$