Which of the following is a correct method to calculate the partial pressure exerted by a gas in a mixture?

• A. Multiply the mole fraction of the gas by the total pressure of the mixture.
• B. Subtract the vapor pressure of water from the total pressure.
• C. Add the molar mass of the gas to the total pressure.
• D. Divide the total pressure of the mixture by the number of gases present.

Answer: (A)

Verified step by step guidance

1. Understand that the partial pressure of a gas in a mixture is the pressure that gas would exert if it alone occupied the entire volume at the same temperature.
2. Recall Dalton's Law of Partial Pressures, which states that the total pressure of a gas mixture is the sum of the partial pressures of each individual gas.
3. Know that the mole fraction of a gas, denoted as \(x_i\), is the ratio of the number of moles of that gas to the total number of moles in the mixture: \(x_i = \frac{n_i}{n_{total}}\).
4. Use the formula for partial pressure: \(P_i = x_i \times P_{total}\), where \(P_i\) is the partial pressure of the gas, \(x_i\) is its mole fraction, and \(P_{total}\) is the total pressure of the gas mixture.
5. Recognize that other options like subtracting vapor pressure, adding molar mass, or dividing total pressure by the number of gases do not correctly calculate partial pressure according to Dalton's Law.