Question

A hydrocarbon contains 17.2% of hydrogen and has a relative molecular mass of 58. Its molecular formula is:
(Given: Atomic masses of: C = 12 g, H = 1 g)

• A. $C_2{H}_5$
• B. $C_2{H}_4$
• C. $C_4{H}_{10}$
• D. $C_4{H}_8$

Answer 1

The correct option is C $C_4{H}_{10}$

$\begin{array}{ccccc}\text{Element}& \text{\% wt.}& \text{At. wt.}& \text{Relative no. of moles}& \text{Simple ratio of atoms}\\ C& 82.8& 12& 82.8/12=6.9& 6.96/6.9=1\\ H& 17.2& 1& 17.2/1=17.2& 17.7/6.9=2.5\end{array}$
Empiricl formula of the compoud $=C_2{H}_5$
Empirical formula weight of hydrocarbon $=2\times 12+5=29$

$\because \text{Molecular wt.}=n\times \text{Empirical formula}$
$\Rightarrow n=58/29=2$

$\therefore \text{Empirical formula}=C_4{H}_{10}$