Question

The equivalent mass of an element is 4. Its chloride has vapour density 59.25. Then the valency of the element is:

• A. 4
• B. 2
• C. 3
• D. 1

Answer 1

The correct option is C 3

Equivalent mass of an element=$4$

Vapour density of $C{l}^{-}=59.25$

To find:- Valency of element

Formula:- Let the compound be $MC{l}_x$

$x$ is valency of $M$

(Refer to Image)

Molecular weight= $2\times$ Vapour density....(i)

$\therefore$ Molecular weight of $MC{l}_x=2\times 59.25=118.5$....(ii)

Also, molecular weight

$\therefore M+x\times 35.5=118.5$....(iii) [$M⟶$ Atomic mass of $M$, $x⟶$ Number of atom of $Cl$]

$\therefore M+35.5x=118.5$....(iv)

We know,

Equivalent weight=$\frac{Atomicmass}{Valency}$....(v)

$\Rightarrow 4=\frac{M}{x}$....(Atomic mass=$M$ from (iii))

$\therefore M=4x$....(vi)

Putting value of $M$ in equation (iv)

$\Rightarrow 4x+35.5x=118.5$

$\Rightarrow 39.5x=118.5$

$\therefore x=\frac{118.5}{39.5}=3$

$\therefore$ Valency of the element is $3$.