Question

A metal M, forms a volatile chloride containing 65.5% Chlorine. If the density of the chloride relative to hydrogen is 162.5, find the molecular formula of the chloride. [M = 56, Cl = 35.5]

Answer 1

Given, density of chloride relative to hydrogen = 162.5
Percentage of chlorine = 65.5‰
Percentage of Metal M = 100 - 65.5 = 34.5‰

Element	Atomic mass	Percentage	Relative  number of moles	Simplest mole ratio	Whole number ratio
M	56	34.5	34.5/56 = 0.62	0.62/0.62 = 1	1
Cl	35.5	65.5	65.5/35.5 =1.85	1.85/0.62 = 2.98	3

Empirical formula = MCl₃
Empirical formula mass = 56 + 3 x 35.5 = 162.5
Molecular mass = 2 x Vapour density = 2 x 162.5 = 325
n = Molecular mass / Empirical formula mass
= 325/162.5 = 2
Molecular formula = n x empirical formula
= 2 X MCl₃ = M₂Cl₆