Question

The empirical formula of a compound is $CH _{2}$. One mole of this compound has a mass of $42\, g$. Its molecular formula is :

• A. $C_{3}H_{6}$
• B. $C_{3}H_{8}$
• C. $CH_{2}$
• D. $C_{2}H_{2}$

Answer 1

Answer: (A)

$C_{3}H_{6}$

Answer 2

Weight of empirical formula $CH _{2} =12+(1 \times 2)$ $4=12+2$ $=14$ Mass of one mole of the compound = its molecular weight $=42$ $n=\frac{\text { Mol. wt. }}{\text { Empirical formula wt.}}=\frac{42}{14}=3$ $\therefore$ Mol. formula =( Empirical formula) $\times n$ $=\left( CH _{2}\right) \times 3= C _{3} H _{6}$