Ch.6 - Gases

Problem 66

Chapter 6, Problem 66

A sample of gas has a mass of 0.555 g. Its volume is 117 mL at a temperature of 85 °C and a pressure of 753 mmHg. Find the molar mass of the gas.

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Convert the temperature from Celsius to Kelvin by adding 273.15 to the Celsius temperature.

Convert the pressure from mmHg to atm using the conversion factor: 1 atm = 760 mmHg.

Use the Ideal Gas Law equation, PV = nRT, to solve for the number of moles (n) of the gas. Remember to use the appropriate units: P in atm, V in liters, R = 0.0821 L·atm/mol·K, and T in Kelvin.

Calculate the number of moles (n) by rearranging the Ideal Gas Law to n = PV / RT.

Determine the molar mass of the gas by dividing the mass of the gas sample by the number of moles calculated in the previous step.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ideal Gas Law

The Ideal Gas Law is a fundamental equation in chemistry that relates the pressure, volume, temperature, and number of moles of a gas. It is expressed as PV = nRT, where P is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is temperature in Kelvin. This law allows us to calculate the behavior of gases under various conditions and is essential for determining the molar mass of a gas from its physical properties.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by dividing the mass of the gas sample by the number of moles present. Understanding molar mass is crucial for converting between mass and moles, which is necessary for stoichiometric calculations and determining the identity of a gas based on its physical properties.

Gas Properties and Conditions

Gas properties, including pressure, volume, and temperature, are interrelated and can significantly affect the behavior of a gas. Pressure is the force exerted by gas particles colliding with the walls of their container, while volume is the space the gas occupies. Temperature, measured in Kelvin, reflects the kinetic energy of gas particles. Recognizing how these properties interact is vital for applying the Ideal Gas Law and solving for unknowns like molar mass.

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