The hydrogen gas formed in a chemical reaction is collected...

The hydrogen gas formed in a chemical reaction is collected over water at $30.0^{\circ} \mathrm{C}$ at a total pressure of 732 $\mathrm{mm} \mathrm{Hg.}$ . What is the partial pressure of the hydrogen gas collected in this way? If the total volume of gas collected is $722 \mathrm{mL},$ what mass of hydrogen gas is collected?

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Key Concepts

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature. In gas collection over water, the water vapor's contribution must be accounted for, as it affects the measurement of the collected gas's pressure and, consequently, the calculations based on that pressure.

Ideal Gas Law

The ideal gas law, expressed as PV = nRT, provides a relationship among pressure, volume, temperature, and the number of moles of a gas. This law is central in calculating the amount (in moles) of a gas from conditions provided, and then converting that quantity to mass using the gas's molar mass.

Dalton's Law of Partial Pressures

This law states that in a mixture of non-reacting gases, the total pressure is the sum of the partial pressures of each individual gas. When collecting a gas over water, the vapor pressure of water contributes to the total pressure, so the unknown gas's pressure must be determined by subtracting the water vapor pressure from the total measured pressure.

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