Answer to Question #160770 in General Chemistry for Karrie

Question

Hydrogen produced from a hydrolysis reaction was collected over water. The total volume of h₂ (g) was 93.26 at the temperature of 25 degree C. The barometric pressure was 742 mmHg and the vapor pressure of water at 25 degrees C was 24.0 mmHg. Calculate the moles of hydrogen gas produced by the reaction

Answer 1

Convert mmHg to Pa: 742 mmHg is 98925.2 Pa, 24 mmHg is 3199.74 Pa. Assume the unit of volume is L (so that it is 93.26 L).

The barometric pressure is total pressure of the gas and water vapor:

$$P_B=P_V+P_{\text{H}_2}\space\rightarrow\\ P_{\text{H}_2}=P_B-P_V.$$

Now apply the ideal gas law:

$$PV=nRT,\\\space\\ n=\frac{PV}{RT}=\frac{(P_B-P_V)V}{RT},\\\space\\ n=\frac{(98925.2-3199.74)93.26\cdot10^{-3}}{8.314(273+25)}=3.6\text{ mol}.$$