Question

An organic compound has the following percentage composition C = 12.36 %, H = 2.13 %, Br = 85 % . its vapour density is 94. find its molecular formula?

Answer 1

Vapor density is the density of a vapour in relation to that of hydrogen. It may be defined as mass of a certain volume of a substance divided by mass of same volume of hydrogen.

vapor density = mass of n molecules of gas / mass of n molecules of hydrogen

Therefore:

vapor density = molar mass of gas / molar mass of H2

vapor density = molar mass of gas / 2.016

vapor density = ~½ × molar mass

(and thus: molar mass = ~2 × vapour density)
therefore molecular mass is 188 so molecula formula will be C2H4Br2