Question

$10g$ of hydrofluoric acid gas occupies $5.6$ litre of volume at $NTP$. If the empirical formula of the gas is $HF$, then its molecular formula will be: (At. mass of $F=19$)

• A. $HF$
• B. $H_3{F}_3$
• C. $H_2{F}_2$
• D. $H_4{F}_4$

Answer 1

Answer: (C)

$H_2{F}_2$

$\begin{array}{c}5.6L\text{contain}10g\text{HF gas}\\ \\ 22.4L\text{will contain}=\frac{10}{5.6}\times 22\cdot 4=40g\\ \\ \text{i.e. Molecular mass}=40g\\ \\ \text{Empherical Formula mass}=20\end{array}$

$\begin{array}{c}n=\frac{40}{20}=2\\ \\ \text{Thus, Molecular Formula}=H_2{F}_2\\ \\ \text{Hence option}C\text{is correct.}\end{array}$