Question

1 A natural gas has the following composition on volume basis
CH4-83.5%, C2 H2 - 9% and N2 - 7.5%. Calculate
i) composition in mole %.
ii) the composition in weight %​

Answer 1

Explanation:

The results are in the table below.

l

Item

m

m

CH

4

m

C

2

H

6

m

N

2

m

l

Total

−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

Vol. %

m

m

l

83.6

m

l

l

12.5

m

m

l

4

m

m

l

100

Mole %

m

l

l

l

83.6

m

l

l

12.5

m

m

l

4

m

m

l

100

−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

Moles

m

m

l

l

83.6

m

l

l

12.5

m

m

l

4

m

m

l

100

Mass/g

m

1341

m

m

375.8

m

110

m

m

1829

−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

Mass %

m

l

l

l

73.3

m

l

l

20.6

m

m

l

6

m

m

l

100

Mole percent

Since

n

∝

V

, the volume percent is the same as the mole percent,

Mass percent

Assume that we have 100 mol of gas. Then we have

83.6 mol CH

4

,

12.5 mol C

2

H

6

, and

4 mol N

2

Mass of CH

4

=

83.6

mol CH

4

×

16.04 g CH

4

1

mol CH

4

=

1341 g CH

4

Calculate the masses of ethane and nitrogen in the same way.

Total mass = (1341 + 375.8 + 110) g = 1829 g

% CH

4

=

Mass of CH

4

Total mass

×

100

%

=

1341

g

1828

g

×

100

%

=

73.3

%

Calculate the mass percent of ethane and nitrogen in the same way.