Chemistry, asked by ahassan4843786, 10 months ago

Which one of the following is molecular formula of hydrocarbon which contain 80% by mass of

carbon and 20% by mass of hydrogen?

A) CH4 B) C2H6 C) C3H6 D) C4H8​

Answers

Answered by hrocks4u
1

Answer:

b) C2H6

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BECAZ IT WORTHS

Answered by arnavmadan
2

Explanation:

As with all these problems, it is usually assumed that we have a

100

g

mass of unknown compound, and we work out the molar quantities:

And thus

moles of carbon

80

g

12.011

g

m

o

l

1

=

6.66

m

o

l

.

And thus

moles of hydrogen

20

g

1.008

g

m

o

l

1

=

19.8

m

o

l

.

We divide the molar quantities thru by the SMALLER molar quantity:

C

:

6.66

m

o

l

6.66

m

o

l

=

1

H

:

19.8

m

o

l

6.66

m

o

l

=

2.97

And thus the

empirical formula

=

C

H

3

And we know that the molecular formula is always a multiple of the empirical formula, and thus is terms of mass:

i.e.

molecular formula

=

n

×

empirical formula

But we have a molecular mass of

30

amu

So

30

amu

=

n

×

(

12.01

+

3

×

1.01

)

amu

Clearly,

n

=

2

, and the MOLECULAR FORMULA is

C

2

H

6

.

This is not a realistic problem, as few analysts would perform combustion on a liquid, and no analyst could perform combustion on a gas.

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