Question

A hydrocarbon of vapour density 15 has 80 % carbon. Calculate the molecular
formula of the hydrocarbon.​

Answer 1

Explanation:

A hydrocarbon contains 80% of carbon.

means, mass percentage of C = 80%

then mass percentage of H = 20% .

find percentage atomic mass ratio,

for C ⇒80/12 = 20/3

for H ⇒20/1 = 20

find simple ratio of given numerical value.

C : H = 20/3 : 20 = 1 : 3

so, empirical formula of hydrogen is CH_3CH

3

as it is given, vapor density of hydrogen is 30.

so, molar mass of hydrogen = 2 × vapor density

= 2 × 30 = 60 g/mol.

now, molecular mass = n × mass of empirical formula

60 = n (12 × 1 + 1 × 3)

n = 4

hence, molecular formula of hydrocarbon is C_4H_{12}C

4

H

12