Question

Find the molecular formula fo a hydrocarbon having vapour density 15, which contains 20% of Hydrogen.

Answer 1

As we know that hydrocarbons are the organic compounds that contain only carbon and hydrogen..

Given,

C = 80%, H = 20%

Therefore, in 100 g of compound,

C = 80g

H = 20g

Atomic mass of H= 1

Atomic mass of C = 12

Thus

moles of C = = 6.667

moles of H = 20

Since 6.667 is the smallest value, division by it gives a ratio 1 : 3

Thus the empirical formula of the above compound is

For empirical formula mass is :

1 12 + 3 1 = 15g

Since vapour density = molar mass,

then the molar mass = vapour density 2 = 215=30

Now

$\frac{\text{Molar mass}}{\text{Empirical formula mass}}=\frac{30}{15}=2=n$

Multiplying the empirical formula by n we get the molecular formula

=

Hence the molecular formula of the compound is