Question

1.520 g of a metal hydroxide on ignition gave 0.995 g of oxide. The equivalent mass of the metal is:

• A. 1.52 g
• B. 0.995 g
• C. 19 g
• D. 9 g

Answer 1

The correct option is D 9 g

Let's asssume the valency of the metal to be 'x'.
Metal hydroxide = $M(OH{)}_x$
Metal oxide = $M{O}_x$
As per the question, the metal hydroxide on ignition gave the metal oxide.
Equivalent weight of metal hydroxide $\left[M\right(OH{)}_x]$ = Equivalent weight of metal oxide $\left[M{O}_x\right]$
$\frac{W_{M(OH{)}_x}}{E_{M(OH{)}_x}}$ = $\frac{W_{M{O}_x}}{E_{M{O}_x}}$
$\Rightarrow \frac{1.52}{E_{metal}+E_{O{H}^{-}}}$ = $\frac{0.995}{E_{metal}+E_{oxygen}}$
$E_{O{H}^{-}}$ = $\frac{\frac{\text{Molar mass}}{O{H}^{-}}}{\text{charge}}$ = $\frac{17}{1}$
Similarly, $E_{oxygen}$ = $\frac{16}{2}$ = 8
$\frac{1.52}{E_M+17}$ = $\frac{0.995}{E_M+8}$
On solving, $E_M=9$ g