A 2.00 -L sample of O2(g) was collected over water at a...

A 2.00 -L sample of $\mathrm{O}_{2}(g)$ was collected over water at a total pressure of 785 torr and $25^{\circ} \mathrm{C}$ . When the $\mathrm{O}_{2}(g)$ was dried (water vapor removed), the gas had a volume of 1.94 $\mathrm{L}$ at $25^{\circ} \mathrm{C}$ and 785 torr. Calculate the vapor pressure of water at $25^{\circ} \mathrm{C}.$

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Key Concepts

Collection of Gases Over Water

When gases are collected over water, the measured pressure includes the contribution from water vapor. Recognizing and correcting for this contribution is necessary to accurately determine the properties of the gas alone and to calculate the vapor pressure of water at the collection temperature.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its condensed phases (solid or liquid) at a given temperature. It is an important property in understanding how gases and vapors behave, especially in systems where a liquid is present and contributes additional pressure.

Dalton's Law of Partial Pressures

This law states that in a mixture of non-reacting gases, the total pressure is equal to the sum of the individual partial pressures of each gas. It is a critical concept when analyzing gas mixtures, such as a gas collected over water, where water vapor exerts its own pressure in addition to the gas of interest.

Ideal Gas Law

The ideal gas law, expressed as PV = nRT, relates the pressure, volume, temperature, and number of moles of a gas. It serves as the foundation for quantitative calculations in gas behavior and is essential for determining the molar amount of gases under different conditions.

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