Question

The equivalent weight of an element is 4. Its chloride has a vapour density 59.25. Then, the valency of the element is:
A.4
B.3
C.2
D.1

Answer 1

We know that Molecular mass = 2 $\times$ vapour density. We can calculate the molecular mass of the compound and then we can find the combined weight.

Complete step by step answer:
Given,
Let that element be, M
Equivalent weight of an element = 4
Compound = $MC{l_x}$
Vapour density of its chloride = 59.25
It means that the 4 g of the element combines with 35.5 g of chlorine.
Molecular mass = 2 $\times$ vapour density
Molecular mass = 2 $\times$ 59.25 = 118.5
Since, 4 g of this element combines with 35.5 g of chlorine. They will be in the package and then the combined weight will be 39.5
We can calculate the molecular mass by summing the atomic weight of the atoms making up the substance molecular formula
molecular mass = $x \times 4 \times x \times 35.5$ (where, x is the valency of the element)
$\Rightarrow$ 118.5 = $x \times 4 \times x \times 35.5$
$\Rightarrow$ $4x + 35.5x = 118.5$
$\Rightarrow$ $39.5x = 118.5$
$\Rightarrow$ $X = 3$
So, the valency will be 3.

Therefore, the correct answer is option (B).

Note:
This question can also be solved by an alternate method,
Let that element be M and x be the valency of the element.
Equivalent weight of an element = 4
Substance = $MC{l_x}$
Molecular weight of = 2 $\times$ 59.25 = 118.5
Equivalent weight of (M + Cl) $= \dfrac{{Molecular\,Weight}}{x}$
$\therefore \dfrac{{Molecular\,Weight}}{{4 + 35.5}} = \dfrac{{118.5}}{{4 + 35.5}} = 3$
So, the valency will be 3