Difficulty: Easy
Correct Answer: Dalton’s law of partial pressures
Explanation:
Introduction / Context:
When a gas sample is collected over water, the measured pressure includes contributions from both the dry gas and water vapor. Accurately determining the dry gas volume requires correcting for the water vapor’s partial pressure. This is a staple calculation in physical chemistry and gas analysis.
Given Data / Assumptions:
Concept / Approach:
Dalton’s law states that the total pressure of a gas mixture equals the sum of the partial pressures of its components. Thus, P_dry gas = P_total − P_water(vapor). Once P_dry gas is known, use the ideal gas relation to compute moles or corrected volume of the dry gas at the same conditions.
Step-by-Step Solution:
Verification / Alternative check:
If the collection temperature is lowered, P_sat,water decreases, making the water-vapor correction smaller—consistent with Dalton’s framework and observed behavior.
Why Other Options Are Wrong:
Common Pitfalls:
Forgetting to subtract P_sat,water or using the wrong temperature for P_sat lookup will skew the dry-gas calculation.
Final Answer:
Dalton’s law of partial pressures
Discussion & Comments