Question

A 0.2 mole sample of hydrocarbon ${{\text{C}}_{\text{x}}}{{\text{H}}_{\text{y}}}$yields after complete combustion with excess ${{\text{O}}_{\text{2}}}$ gas, 0.8 mole of${\text{C}}{{\text{O}}_{\text{2}}}$, 1mole of${{\text{H}}_{\text{2}}}{\text{O}}$. Hence the hydrocarbon is
A. ${{\text{C}}_{\text{4}}}{{\text{H}}_{{\text{10}}}}$
B. ${{\text{C}}_{\text{4}}}{{\text{H}}_{\text{8}}}$
C. ${{\text{C}}_{\text{4}}}{{\text{H}}_{\text{5}}}$
D. ${{\text{C}}_{\text{8}}}{{\text{H}}_{{\text{16}}}}$

Answer 1

Hint: The compounds consisting of hydrogen and carbon only are called hydrocarbons. They are obtained from the major sources of energy like petroleum and coal. Compressed natural gas (CNG) and liquefied petroleum gas (LPG) are the primary sources of energy for the automobile industry, and domestic fuel is obtained from petroleum.

Complete step by step answer:
${{\text{C}}_{\text{x}}}{{\text{H}}_{\text{y}}} + {\text{(x + }}\dfrac{{\text{y}}}{{\text{2}}}{\text{)}}{{\text{O}}_{\text{2}}} \to {\text{xC}}{{\text{O}}_{\text{2}}}{\text{ + }}\dfrac{{\text{y}}}{{\text{2}}}{{\text{H}}_{\text{2}}}{\text{O}}$
So 1 mole of ${C_x}{H_y}$will produce ${\text{x}}$mole of ${\text{C}}{{\text{O}}_{\text{2}}}$and $\dfrac{{\text{y}}}{{\text{2}}}$mole of ${{\text{H}}_{\text{2}}}{\text{O}}$
So, $0.2$mole of ${C_x}{H_y}$will produce$\dfrac{{\text{x}}}{5}$mole of ${\text{C}}{{\text{O}}_{\text{2}}}$and $\dfrac{{\text{y}}}{{10}}$mole of ${{\text{H}}_{\text{2}}}{\text{O}}$
$\dfrac{{\text{x}}}{5}$mole of ${\text{C}}{{\text{O}}_{\text{2}}}$=$0.8$mole and $\dfrac{{\text{y}}}{{10}}$=1 mole
${\text{x = 4}}$and${\text{y = 10}}$
Hence the hydrocarbon is ${{\text{C}}_{\text{4}}}{{\text{H}}_{{\text{10}}}}$ i.e. butane.

So, the correct answer is Option A.

Additional Information:
Combustion is a process of burning some substances at high-temperature. It is an exothermic reaction which happens between fuel and oxygen, producing a gaseous substance (smoke) as a product. Combustion is of two types, one is complete combustion and another is incomplete combustion. Whereas, the Hydrocarbons are compounds made only with the elements of hydrogen and carbon. Hydrocarbons are broadly classified as alkanes, alkenes, and alkynes.

Note: A hydrocarbon is a compound made of only 2 elements namely carbon and hydrogen atoms. The interesting thing is, it is found in crude oil and can be separated by dfractional distillation. The bond between them is non-polar covalent bonds. In the presence of an excess of air, complete combustion of a hydrocarbon produces carbon dioxide and water as products In further. In order to achieve the complete combustion of hydrocarbon, oxygen should be in excess and hydrocarbon is treated as limiting reagents.