Question

A gaseous hydrocarbon weights 0.70 g. and contains 0.60 g. of carbon. Find the molecular formula of the compound if it’s molecular weight is 70. [C = 12, H = 1]

August 2, 2024

Answer

H = 0.70 – 0.60 = 0.1 g

Element	% composition	At. wt.	Relative no. of atoms	Simplest ratio
Carbon	× 100 = 85.71	12	= 7.142	= 1
Hydrogen	× 100 = 14.28	1	= 14.28	= 2

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

Hence, empirical formula is CH₂

Empirical formula weight = 12 + 2(1) = 14

Molecular weight = 70

n = $Molecular\ weight\over Emperical\ Formula\ Weight$

= $70\over 14$ = 5

Molecular formula = (CH₂)₅ = C₅H₁₀

Hence, Molecular formula = C₅H₁₀

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