Question

The vapour density of a hydrocarbon is 30. If on
complete combustion of hydrocarbon, 8.8 g CO2
and 5.4 g H,O are obtained then the molecular
formula of hydrocarbon is​

Answer 1

Answer:

Solution

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Correct option is

B

C

4

H

12

C

x

H

y

+(x+

2

y

)O

2

⟶xCO

2

+

2

y

H

2

O

Moles of CO

2

=x=

44

8.8

=0.2 moles.

Moles of H

2

O=

2

y

=

18

5.4

=0.3 moles.

∴x=0.2 and y=0.6⟹

y

x

=

3

1

Empirical formula of hydrocarbon is CH

3

.

Now, vapor density =

2

M

∴ M=2×30=60 g/mol

∴ (x×12)+(y×1)=60

12x+y=60

12x+3x=60

∴15x=60

∴x=4 and y=12

Therefore the molecular formula of hydrocarbon is C

4

H

12

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.