Question

A definite amount of gaseous hydrocarbons was burnt with just sufficient amounts of ${O_2} $. The volume of all reactants was $600ml$, after the explosion the volume of products $[C {O_2} (g) {{and}} {H_2} O (g)] $ was found to be $700ml$ under the similar conditions. The molecular formula of the compound is:
A.${C_3}{H_8}$
B.${C_3}{H_6}$
C.${C_3}{H_4}$
D.${C_4}{H_{10}}$

Answer 1

Hint: Molecular formula or chemical formula, defines the type of atom. It can specify simple structures of simple molecular formula they are known as the empirical formula. They are used in chemical equations, which describe the chemical reaction.

Complete answer:
First we have to write the molecular formula for the compound, since we don’t know how many carbons and oxygen we have been given we will assume carbons to be ‘x’ amount and hydrogen to be ‘y’.
${C_x} {H_y} + (x + \dfrac{y}{4}){O_2} \to xC {O_2} $, here we have the unbalanced equation
${C_x} {H_y} + {O_2} \to xC {O_ {_2}} + \dfrac{y}{2}{H_2}O$, this is the balanced equation for the combustion reaction
Placing the values in given equation we get $\dfrac {{700}} {{600}} = \dfrac {{(x + 0.5y)}} {{1 + x + 0.25y}} $
Solving on both the sides we get
$\dfrac {7} {6} = \dfrac{{2x + y}} {{2 + 2x + 0.5y}} $
$\dfrac {7} {{12}} = \dfrac{{2x + y}} {{4 + 4x + y}} $
Simplifying the equation
$28 + 28x + 7y = 24x + 12y$
 Rearrange the equation,
$28 + 4x = 5y$
Now solving for ‘x’ and ‘y’ we
$
  x = 3 \\
  y = 8 \\
 $
Therefore the molecular formula for the compound will be ${C_3} {H_8} $.
So the correct option will be option A) ${C_3} {H_8} $.

Note:Hydrocarbons are organic compounds consisting of carbons and hydrogens. They are colourless, and hydrophobic. Gaseous hydrocarbons are natural gases consisting primarily of methane and other higher alkanes also carbon dioxide, nitrogen and hydrogen sulphide. They have lower boiling points, low viscosity, and higher flammability. Hydrocarbons are main components in petroleum industry and natural gas industries. They serve as raw materials in plastics, rubber and chemical industries.