Question

If the vapour density of a carbon containing gasrous substance is 13 which of the following its molecular formula

Answer 1

Solution :

C=80%

H=100=80%=20%

Therefore , in 100 g of compound,

C=80g

H=20g

Atomic mass of H=1

Atomic mass of C=12

thus

model of C=8012=6.667

model of H=201=20

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

Thus the emprical formula of the above compound is CH3

For CH3 empirical formula mass is

1∗12+3∗1=15g

Since vapor density =12 molar mass

then the molar mass = vapour density *2 =2 *30 or 60

Now

Molar mass / Empirical formula mass =6015=4=(n)

Multiplying the empirical formula by n we get the molecular formula =C4H12

Hence the molecular formula of the compound is C4H12