A piece of sodium metal reacts completely with water as...

A piece of sodium metal reacts completely with water as follows: $$2 \mathrm{Na}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow 2 \mathrm{NaOH}(a q)+\mathrm{H}_{2}(g)$$ The hydrogen gas generated is collected over water at $25.0^{\circ} \mathrm{C}$. The volume of the gas is $246 \mathrm{mL}$ measured at 1.00 atm. Calculate the number of grams of sodium used in the reaction. (Vapor pressure of water at $25^{\circ} \mathrm{C}=0.0313$ atm.

A piece of sodium metal reacts completely with water as follows:
$$2 \mathrm{Na}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow 2 \mathrm{NaOH}(a q)+\mathrm{H}_{2}(g)$$
The hydrogen gas generated is collected over water at $25.0^{\circ} \mathrm{C}$. The volume of the gas is $246 \mathrm{mL}$ measured at 1.00 atm. Calculate the number of grams of sodium used in the reaction. (Vapor pressure of water at $25^{\circ} \mathrm{C}=0.0313$ atm.

Key Concepts

Gas Collection Over Water

When gases are collected over water, the measured pressure is a combination of the pressure of the gas of interest and the vapor pressure of water. To obtain the correct pressure of the gas, one must subtract the water vapor pressure from the total pressure, which is crucial for subsequent calculations.

Vapor Pressure of Water

Vapor pressure is the pressure exerted by water vapor in equilibrium with liquid water at a given temperature. In gas collection experiments conducted over water, this property must be taken into account to correct the measured pressure and accurately determine the amount of gas produced.

Ideal Gas Law

The Ideal Gas Law (PV = nRT) is a key principle used to relate the pressure, volume, temperature, and number of moles of a gas. By using the corrected gas pressure, along with the measured volume and temperature, one can calculate the moles of gas present, which is essential in stoichiometric calculations.

Reaction Stoichiometry

Reaction stoichiometry involves using the balanced equation to relate the moles of reactants and products. In this context, the stoichiometric relationship between sodium and hydrogen gas in the reaction allows for the conversion of the moles of hydrogen produced to the moles of sodium consumed in the reaction.

Molar Mass

Molar mass is the mass of one mole of a substance, serving as a conversion factor between moles and grams. Knowing the molar mass of sodium is essential to convert the calculated moles of sodium into grams, thereby determining the mass of sodium used in the reaction.

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