Question

A compound is made up of two elements a and b, has a = 70% and b = 30%. The relative number of moles of a and b in the compound are 1.25 and 1.88 respectively. If the molar mass of the compound is 160, find the molecular formula of the compound.

Answer 1

Answer:

Relative no. of moles of an element

Atomic mass of B = 30/1.88 = 16

Calculation of Empirical formula

Element Relative no. of moles Simplest molar ratio Simplest whole no. molar ratio

A 1.25 1.25/1.25 = 1 2

B 1.88 1.88/1.25 = 1.5 3

Empirical formula = A2B3

Calculation of molecular formula

Empirical formula mass = 2 x 56 + 3 x 16 = 160

n = molecular mass / Empirical formula mass = 160/160 = 1 Molecular formula = A2B3

Answer 2

Explanation:

Here,Relative number of moles=% composition/atomic mass

ie;Z=%/Relative number of moles

Z of A=70/1.25=56

Z of B=30/1.88=16

Dividing by least value

1.25/1.25=1=2

1.88/1.25=1.5=3

That is Emperical Formula A2B3

Emperical Formula Mass=2*56+3*16=160

n=Emperical Formula mass/Molecular mass

=160/160=1

Molecular Formula=1*Emperical Formula=A2B3