Equal masses of $\mathrm{H}_{2(\mathrm{~g})}$ and $\mathrm{He}_{(\mathrm{g})}$ are enclosed in a container…

Equal masses of $\mathrm{H}_{2(\mathrm{~g})}$ and $\mathrm{He}_{(\mathrm{g})}$ are enclosed in a container at constant temperature. The ratio of partial pressure of $\mathrm{H}_2$ to $\mathrm{He}$ is
  1. $1: 1$
  2. $1: 2$
  3. $2: 1$
  4. $1: 4$

Solution

Let the mass be ' $x$ '. $\mathrm{n}_{\mathrm{H}_2}=\frac{\mathrm{xg}}{2 \mathrm{~g} \mathrm{~mol}^{-1}}=\frac{\mathrm{x}}{2}$ $\begin{aligned} & \mathrm{n}_{\mathrm{He}}=\frac{\mathrm{xg}}{4 \mathrm{~g} \mathrm{~mol}^{-1}}=\frac{\mathrm{x}}{4} \\ & \mathrm{n}_{\text {Total }}=\frac{3 \mathrm{x}}{4} \end{aligned}$ Now, $\begin{aligned} & x_{\mathrm{H}_2}=\frac{\mathrm{n}}{\mathrm{n}_{\text {Total }}}=\frac{\mathrm{x} / 2}{3 \mathrm{x} / 4}=\frac{2}{3} \\ & x_{\mathrm{H}_e}=\frac{\mathrm{n}}{\mathrm{n}_{\text {Total }}}=\frac{\mathrm{x} / 4}{3 \mathrm{x} / 4}=\frac{1}{3} \end{aligned}$ Now, $\begin{gathered} \mathrm{P}_{\mathrm{H}_2}=x_{\mathrm{H}_2} \times \mathrm{P}_{\text {Tótal }}=\frac{2}{3} \times \mathrm{P} \\ \mathrm{P}_{\mathrm{He}}=x_{\mathrm{He}} \times \mathrm{P}_{\text {Total }}=\frac{1}{3} \times \mathrm{P} \\ \mathrm{P}_{\mathrm{H}_2}: \mathrm{P}_{\mathrm{H}_{\mathrm{e}}}=\frac{2 / 3 \mathrm{P}}{1 / 3 \mathrm{P}}=2: 1 \end{gathered}$

Asked in: MHT CET 2023 (12 May Shift 2)

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