Question

In what mass of water must $25g$ of $CuSO_{4}.5H_{2}O$ be dissolved to obtain an $8\%$ solution of $CuSO_{4}$ ? $\left(At . wt . of Cu = 63 . 5\right)$
Round off answer to the nearest integer value.

Answer 1

$25gofCuSO_{4}.5H_{2}O$
$\because 249.5gofCuSO_{4}.5H_{2}O$ contain $159.5gofCuSO_{4}$
$\therefore 1g\text{of}CuSO_{4}.5H_{2}O\text{contains}\frac{159 . 5}{249 . 5}g\text{of}CuSO_{4}$
$\therefore 25g\text{of}CuSO_{4}.5H_{2}O\text{contains}\frac{159 . 5}{249 . 5}\times 25=15.98g\text{of}CuSO_{4}$
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 $=199.75-25=174.75g$