Final answer:
The partial pressure of hydrogen gas is calculated by subtracting the known vapor pressure of water from the total gas pressure. Then, applying the ideal gas law with the partial pressure, volume, and temperature provides the mass of the collected hydrogen gas.
Step-by-step explanation:
The question concerns the calculation of the partial pressure of hydrogen gas and the mass of hydrogen gas collected during a chemical reaction where the gas is collected over water. According to Dalton's Law of Partial Pressures, the total pressure of a gas mixture is equal to the sum of the individual partial pressures of each gas in the mixture. Since the hydrogen gas is collected over water, we must account for the vapor pressure of water at the given temperature when calculating the partial pressure of the hydrogen gas. In this scenario, the total pressure is 732 mm Hg and the vapor pressure of water at 30°C (which must be looked up in a reference table) must be subtracted from this total to determine the partial pressure of the hydrogen gas. To determine the mass of the hydrogen gas, we use the ideal gas law, which involves the calculated partial pressure, the volume of the collected gas (722 mL), and the temperature (30°C). The molar mass of hydrogen gas (H₂) is used in the calculation to find the mass.