Question

16. A gaseous hydrocarbon contains 82.76% of carbon.
Given that its vapour density is 29, find its molecular
formula.
(2016)​

Answer 1

Answer:

Therefore molecular formula is given hydrocarbon is C4H10.

Explanation:

Element %composition Mol. mass No. of C atoms Simplest Rounding

ratio off

C 82.76 12 6.89 1× 2 2

H 17.24 1 17.24 2.5× 2 5

Number of carbon atoms present =

12

82.76

=6.89

Number of hydrogen atoms present =

1

17.24

=17.24

simplest ratio =

6.89

6.89

=1

simplest ratio =

6.89

17.24

=2.5

∴ Empirical fromula is C

2

H

5

Empirical formula mass= 2×12+5 = 29

∴ V.D. = 29

Mol. mass = 2 × V.D.

=58

n=

Empiricalformulamass

Molecularmass

=

29

58

=2

∴ Molecular formula = C

4

H

10

.