A 118 -mL flask is evacuated and found to have a mass of 97.129 g . When the flask is filled wit

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A 118 -mL flask is evacuated and found to have a mass of...

A 118 -mL flask is evacuated and found to have a mass of 97.129 $\mathrm{g}$ . When the flask is filled with 768 torr of helium gas at $35^{\circ} \mathrm{C},$ it has a mass of 97.171 $\mathrm{g}$ . Was the helium gas pure?

Key Concepts

Experimental Determination of Gas Purity

Experimental determination of gas purity involves comparing the measured mass of the gas in a container to the mass predicted by calculations based on the ideal gas law and the known molar mass of the pure gas. A significant discrepancy between the measured and expected masses can indicate the presence of impurities or contaminants in the gas sample.

Ideal Gas Law

The ideal gas law (PV = nRT) is a fundamental equation that relates the pressure, volume, temperature, and number of moles of a gas. It allows one to predict the behavior of gases under various conditions and is essential in calculating the expected amount of gas in a given container when the other variables are known.

Molar Mass

Molar mass is the mass per mole of a substance, and it serves as a bridge between the microscopic scale (number of particles or moles) and macroscopic measurements (mass). In gas studies, by using the ideal gas law to determine moles and comparing with the measured mass, one can infer the molar mass and thus assess the purity of the gas.

Pressure Unit Conversion

Pressure unit conversion is critical when applying the ideal gas law, as different systems of units (such as torr, atm, or pascals) may be used. Converting these into a consistent unit ensures that the calculations reflect accurate thermodynamic relationships and comparisons.

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