Question

Oxygen gas generated by the decomposition of potassium chlorate is collected. The volume of oxygen collected at ${24}^{o}C$ and atmospheric pressure of 760 mmHg is 128 mL. Calculate the mass (in grams) of gas obtained. The pressure of the water vapour at ${24}^{o}C$ is 22.4 mmHg.

• A. 1.36 g
• B. 1.52 g
• C. 0.163 g
• D. 1.63 g

Answer 1

The correct option is C 0.163 g

$\begin{array}{c}\text{From the total pressure and the}\text{Vapour pressure of water, we can calculate}\text{the partial pressure of}{O}_2\text{.}\end{array}$

$\begin{array}{c}{P}_{O_2}=P_r-P_{H2O}\\ 760-22.4\\ 737.6mm\text{Hg}=0.974atm\end{array}$

$\begin{array}{c}\text{From the ideal gas equation we}\\ \text{write,}m=\frac{PVM}{RT}\end{array}$

$\begin{array}{c}=\frac{\left(0.974\right)\left(0.128\right)\left(32\right)}{\left(0.0821\right)(273+24)}\\ =0.163g\end{array}$