Question

An organic compound has vapour density 94. It contains C = 12.67%, H = 2.13%, and Br = 85.11%. Find the molecular formula of the organic compound. [C = 12, H = 1, Br = 80]

August 5, 2024

Answer

Element	% composition	At. wt.	Relative no. of atoms	Simplest ratio
Carbon	12.67	12	12.67/12 = 1.05	1.05/1.05 = 1
Hydrogen	2.13	1	2.13/1 = 2.13	2.13/1.05 = 2
chlorine	85.11	80	85.11/80 = 1.06	1.06/1.05 = 1

Simplest ratio of whole numbers = C : H : Br = 1 : 2 : 1

Hence, empirical formula is CH₂Br

Empirical formula weight = 12 + 2(1) + 80

= 94

Vapour density (V.D.) = 94

Molecular weight = 2 × V.D.

= 2 × 94

= 188

$Molecular\ weight\over Empirical\ formula\ weight$

$188\over 94 = 2$

∴ Molecular formula = (CH₂Br)₂ = C₂H₄Br₂

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