Question

Find the empirical and molecular formula of an organic compound from the data given: C = 75.92%, H = 6.32% and N = 17.76%. The vapour density of the compound is 39.5
[C = 12, H = 1, N = 14]

August 5, 2024

Answer

Element	% composition	At. wt.	Relative no. of atoms	Simplest ratio
Carbon	75.92	12	75.92/12 = 6.32	6.32/1.26 = 5
Hydrogen	6.32	1	6.32/1 = 6.32	6.32/1.26 = 5
chlorine	17.76	14	17.76/14 = 1.26	1.26/1.26 = 1

Simplest ratio of whole numbers = C : H : N = 5 : 5 : 1

Hence, the empirical formula is C₅H₅N

Empirical formula weight = 5(12) + 5(1) + 14 = 79

V.D. = 39.5

Molecular weight = 2 × V.D.

= 2 × 39.5 = 79

n = $Molecular\ weight\over Empirical\ formula\ weight$

= $79\over 79$ = 1

∴ Molecular formula = (C₅H₅N)₁ = C₅H₅N

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