Question

50 cc of oxygen is collected in an inverted gas jar over water. The atmospheric pressure is 99.4 kPa and the room temperature is 27°C. The water level in the jar is same as the level outside. The saturation vapour pressure at 27°C is 3.4 kPa. Calculate the number of moles of oxygen collected in the jar.

Answer 1

$\begin{array}{l}\text{Here,}\\ {\text{Atmospheric pressure, P}}_o=99.4\times {10}^3\text{Pa}\\ {\text{SVP at 27}}^{0}C{P}_w\text{= 3}\text{.4}\times {\text{10}}^3\text{Pa}\\ T=300K\\ V=50\times {10}^{-6}{\text{m}}^3\\ \mathrm{Now},\\ \text{Pressure inside the jar = Pressure outside the jar}\left[\text{∵ Level of water is same inside and outside of the jar}\right]\\ \text{Pressure outside the jar = Atmospheric pressure}\\ {\text{Pressure inside the jar = VP of oxygen + SVP of water at 27}}^{0}C\\ \text{⇒}{P}_0=P+P_w\\ \Rightarrow P=P_o-P_w=99.4\times {10}^3-\text{3}\text{.4}\times {\text{10}}^3=96\times {10}^3\\ \text{Applying equation of state, we get}\\ PV=nRT\\ \Rightarrow 96\times {10}^3\times 50\times {10}^{-6}=n\times 8.3\times 300\\ \Rightarrow n=1.9277\times {10}^{-3}\text{mol}\approx \text{1}\text{.93}\times {\text{10}}^{-3}\text{mol}\end{array}$