Question

A hydrocarbon contains 80% of carbon and its vapour density is 30. The hydrocarbon is:
A.$C{H_3}$
B.${C_2}{H_6}$
C.${C_4}{H_{12}}$
D.All of these

Answer 1

An organic chemical compound made only of hydrogen atoms and carbon atoms is called hydrocarbon. Hydrocarbons are generally hydrophobic in nature.
The hydrocarbon said to be found in the question contains 80 percent of carbon. As hydrocarbons are composed of only carbon and hydrogen, the hydrocarbon to be found has 20 percent of hydrogen.

Complete step by step answer:
The density of a particular vapour in relation to that of hydrogen is known as the vapour density of that particular vapour. Vapour density can also be defined as the ratio of molar mass of the gas and molar mass of hydrogen gas.
The molar mass of hydrogen gas is two. Hence vapour density is equal to molar mass of the gas divided by two. In the given question, the vapour density of the hydrocarbon is 30. So, the molar mass of the hydrocarbon to be found is twice the vapour density. Hence the molar mass of the hydrocarbon to be found is 60.
The hydrocarbon contains 80 percent of carbon which means 80 percent of the molar mass is the amount of carbon present in it.
${\text{Amount of carbon present = }}\dfrac{{{\text{80}}}}{{{\text{100}}}} \times{\text{ molar mass of hydrocarbon}}$
$\therefore {\text{Amount of carbon present = }}\dfrac{{80}}{{100}}{\text{ }} \times {\text{ 60 = 48 g}}$
The molar mass of one carbon atom is 12 g. Hence total number of carbon atoms in the hydrocarbon to be found is as follows,
${\text{Number of carbon atoms = }}\dfrac{{{\text{Amount of carbon present}}}}{{{\text{Molar mass of one carbon atom}}}} = \dfrac{{48}}{{12}}{\text{ }} = {\text{ }}4$
Hence, the number of carbon atoms present in the hydrocarbon is 4.
The hydrocarbon to be found is ${C_4}{H_{12}}$.

Therefore, the correct option is C.

Note:
Hydrocarbon gas is known as natural gas and forms in the Earth’s crust from decomposing organic matter. It is a mixture of different hydrocarbons that condense into liquids at different temperatures.Hydrocarbons are majorly used as a fuel source which is combustible. Natural gas is predominantly made up of methane.