Question

an organic compound contains C=41.37%,H=5.75%, N=16.09% and rest oxygen. If vapour density of compound is 43.3. Find molecular formula.

Answer 1

Dear student

To calculate the empirical formula we take the following chart based on the given data as:

Element	Symbol	%age	atomic mass	moles of the element = %age/at. mass (relative no. of moles)	Simplest molar ratio	Simplest whole no. ratio
Carbon	C	41.37	12	41.37/12 = 3.44	3.44/1.49 = 2.3	2
Hydrogen	H	5.75	1	5.75/1 = 5.75	5.75 /1.49 = 3.85	3
Nitrogen	N	16.09	16	16.09/14 = 1.49	1.49/1.49=1	1

Empirical formula : C₂H₃N

Empirical weight = 24 +3 + 14 = 41

Molecular mass = Vapour density X molar mass of H atoms

Molecular mass =43.3 X 3 = 129.9 g

Molecular weight = n X Empirical weight

n = 3.16

Molecular formula = n X empirical formula

Molecular formula = 3 X C₂H₃N = C₆H₉N₃

Regards