A student collects a gas over water using a eudiometer. The atmospheric pressure is 1.00 atm, and the height difference between the water levels inside and outside the eudiometer is negligible. What is the pressure of the collected gas (pgas)?

• A. 1.00 atm
• B. Greater than 1.00 atm
• C. Less than 1.00 atm
• D. 0.00 atm

Answer: (A)

Verified step by step guidance

1. Understand that when collecting a gas over water, the total pressure inside the eudiometer is the sum of the pressure of the collected gas and the water vapor pressure: \(P_{\text{total}} = P_{\text{gas}} + P_{\text{H_2O}}\).
2. Note that the atmospheric pressure (\(P_{\text{atm}}\)) is given as 1.00 atm, and since the height difference between water levels inside and outside the eudiometer is negligible, the pressure inside the eudiometer equals the atmospheric pressure: \(P_{\text{total}} = P_{\text{atm}}\).
3. Recognize that the water vapor pressure (\(P_{\text{H_2O}}\)) depends on temperature and is always a positive value at temperatures above 0 °C, meaning the collected gas pressure is less than the total pressure.
4. Use the relationship to find the pressure of the collected gas: \(P_{\text{gas}} = P_{\text{total}} - P_{\text{H_2O}}\).
5. Since the height difference is negligible and no temperature or vapor pressure is specified, conclude that the pressure of the collected gas is approximately equal to the atmospheric pressure, i.e., \(P_{\text{gas}} \approx 1.00\) atm.