Question

(A) a compound with empirical formula AB2 has the vapour density equal to its empirical formula weight.find the molecular formula (B)a compound with empirical formula AB has vapour density three times its empirical formula weight.find the molecular formula.

Answer 1

we know vapour density =Molecular weight/2
and Molecular weight=(AB2)n
n is number
vapour density=n/2(AB2)=(AB2)
so n=2
so Molecular formula=A2B4

B) (AB)n/2=(AB)3
n=6
so A6B6 is Molecular formula

Answer 2

Answer:

     Molecular Formula ⇒ A₆B₆

Explanation:

Molecular Formula = {Empirical formula}ₙ

n = Molecular Mass / Empirical Mass = MM / EM

n = MM / EM ----{i}

Vapor density = Molecular mass / 2

Molecular mass = 2.Vapor density ----{ii}

From question - Vapor density = 3 × Empirical Mass ----{iii}

from {ii} and {iii}

Molecular mass = 2 × 3 × Empirical Mass

Molecular mass = 6 × Empirical Mass

6 = Molecular mass / Empirical Mass ----{iv}

from {i} and {iv}

n = 6

Molecular Formula - {Empirical formula}ₙ

                                = {AB}ₙ

                                = {AB}₆

Molecular Formula = A₆B₆