Question

A piece of a metal weighs between 0.5g and 0.6g. When dissolved in dilute H2SO4, 196 mL of hydrogen gas is evolved at S.T.P. If the correct atomic weight of the metal is 65.2, calculate exact weight of metal dissolved in acid.

Answer 1

SOLUTION : We suppose that weight of metal dissolved in acid is $0.55 g$ ( average of $0.5 g \& 0 \cdot 6 g )$.

$\because \quad 196 mLH _{2}$ at S.T.P. evolved by $0.55 g$ metal

$11200 mL H _{2}$ at S.T.P. evolved by $\frac{0.55 \times 11200}{196} g =31.43 g$

Hence, approximate cquivalent weight of metal $=31.43$

Valency $=\frac{\text { at. wt. }}{\text { eq. wt. }}=\frac{65 \cdot 2}{31 \cdot 43}=2 \cdot 07 \approx 2 . \quad$ (as valency is a whole number. )

Hence, the correct cquivalent weight $=\frac{65 \cdot 2}{2}=32 \cdot 6$

Now, $11200 mL H _{2}$ at S.T.P. will be evolved by $32 \cdot 6 g$ metal

$\therefore 196 mL H_{2}$ at S.T.P. will be evolved by $\frac{32 \cdot 6 \times 196}{11200} g =0.57 g$.

Therefore, the exact weight of the metal dissolved in acid $= 0 \cdot 5 7 g$.