Question

1 L of a hydrocarbon weighs exactly as much as 1 litre of $C{O_2}$ under identical conditions of pressure and temperature. Then the molecular formula of the hydrocarbon is:
A. ${C_2}{H_6}$
B. ${C_3}{H_8}$
C. ${C_2}{H_4}$
D. ${C_3}{H_4}$

Answer 1

Hint: The compounds made by the carbon and hydrogen atoms are known as hydrocarbons. They are of two types: saturated and the unsaturated hydrocarbons. The double and triple bonds are there in the saturated hydrocarbons and the single bond is present in the unsaturated hydrocarbons.

Complete answer:
Hydrocarbons form the basis of the crude oil, natural gas and coal and they are the naturally occurring compounds in nature. They are also the source of energy.
1 L of a hydrocarbon weighs exactly as much as 1 litre of $C{O_2}$ under identical conditions of pressure and temperature. At the standard conditions of the temperature and pressure the 22.4 L of a hydrocarbon will occupy as much as 22.4 L of carbon dioxide gas under the similar set of the conditions.
The molecular weight of the gas is 44g/ mol. Therefore the weight of the hydrocarbon will also be the same:
Let us calculate the molecular weights of the hydrocarbons given:
$
  {C_2}{H_6} = (12 \times 2) + (1 \times 6) \\
  = 24 + 6 \\
   = 30 \\
$
$
  {C_3}{H_8} = (12 \times 3) + (1 \times 8) \\
   = 36 + 8 \\
   = 44 \\
$
$\
  {C_2}{H_4} = (12 \times 2) + (1 \times 4) \\
= 24 + 4 \\
  = 28 \\
$.
$
 {C_3}{H_4} = (12 \times 3) + (1 \times 4) \\
   = 36 + 4 \\
   = 40 \\
$

As it is evident from the above calculation that the hydrocarbon ${C_3}{H_8}$has the molecular weight of 44 g/ mol thus it will be similar to the carbon dioxide gas under similar temperature and pressure conditions.

So, the correct answer is Option B.

Note:
Hydrocarbons are highly effective as fuels and their source because they produce water, carbon dioxide and heat on the combustion. The calorific value of the fuel varies and thus the use is mainly directed on that major component as well.