Complete combustion of $0.858 \mathrm{~g}$ of compound $\mathrm{X}$ gives $2.64 \mathrm{~g}$ of…
Complete combustion of $0.858 \mathrm{~g}$ of compound $\mathrm{X}$ gives $2.64 \mathrm{~g}$ of $\mathrm{CO}_{2}$ and $1.26 \mathrm{~g}$ of $\mathrm{H}_{2} \mathrm{O}$. The lowest molecular mass $\mathrm{X}$ can have:
$43 \mathrm{~g}$
$86 \mathrm{~g}$
$129 \mathrm{~g}$
$172 \mathrm{~g}$
Solution
Moles of $\mathrm{C}=\mathrm{n}_{\mathrm{CO}_{2}}=\frac{2.64}{44}=0.06$
$\Rightarrow$ mass of $C=0.72$
Mole of $\mathrm{H}=2 \times$ Moles of $\mathrm{H}_{2} \mathrm{O}=$
$2 \times \frac{1.26}{18}=0.14 \Rightarrow$ mass of $\mathrm{H}=0.14$
Compound does not contains oxygen
So EF $ightarrow \mathrm{C}_{0.06} \mathrm{H}_{0.14} \Rightarrow \mathrm{C}_{3} \mathrm{H}_{7}$ which does not exist so $\mathrm{MF}= \mathrm{C}_6 \mathrm{H}_{14}$
$\Rightarrow$ Lowest M.M. $=86$