What safety equipment should students wear before starting an ideal gas law experiment?

Students must wear a lab coat, splash-proof safety glasses or goggles, and appropriate gloves for the chemicals being handled. These items protect against chemical splashes and vapors during the experiment. Proper personal protective equipment is essential before beginning any laboratory work involving volatile organic compounds.

How should Dumas tubes be prepared before the laboratory session?

Place Dumas tubes in an oven at 125 °C the day before the lab. Two hours before the experiment begins, remove the tubes and place them on a heat-resistant surface to cool. Distribute the cooled tubes to each workstation once they reach room temperature to ensure accurate mass measurements.

What glassware and equipment should be set up at each student workstation?

Each workstation requires a 500-mL Erlenmeyer flask, 500-mL Büchner flask, 400-mL and 100-mL beakers, lab stand, 3-prong clamp, ring fixture with wire gauze, Bunsen burner, thermometer with clamp, latex and silicone tubing, and a rubber stopper. This equipment enables students to safely heat and measure gas properties during the ideal gas law experiment.

How are unknown liquid samples prepared and dispensed to students?

Unknown liquids are transferred into labeled 50-mL brown glass bottles using a volumetric pipette, with at least 20 mL of each organohalide compound. During the lab, instructors dispense 0.5 mL of the unknown into each student's Dumas tube using a syringe and needle. This controlled dispensing ensures consistent sample volumes across all trials.

Why is flame drying necessary during the ideal gas law experiment?

Flame drying removes residual water and volatile liquids from the Dumas tube, ensuring accurate mass measurements. The tube is passed through a Bunsen burner flame until it appears dry, then held away from the flame for one minute to allow vapors to condense. If liquid reappears, the process repeats until no condensation occurs.

What precautions should be taken when using a Bunsen burner with organohalide compounds?

Keep the opening of the Dumas tube away from the flame when flame drying, since three of the organohalides are flammable. Use a test tube holder to safely manipulate the tube during heating. Always work in a fume hood and maintain proper ventilation to prevent vapor accumulation and fire hazards.

What role does a barometer play in measuring ideal gas behavior?

A barometer measures atmospheric pressure, which is essential for calculating gas properties using the ideal gas law equation. The barometer should be placed in an easily accessible location so students can record the current atmospheric pressure during their experiment. This measurement is critical for determining the molar mass of unknown vapors.

Ideal Gas Law

Concepts Instructor Prep Student Protocol

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A gas is simply a dispersed sample of matter that is fluid and expands freely to occupy available space. However, a certain number of gas molecules occupy a specific volume under a defined temperature and pressure. We can describe the behavior of a gas under these parameters using the ideal gas law, which uses the universal gas constant, R, to relate all of these variables.

The universal gas constant is equal to 8.314 joules per mole Kelvin. This equation enables us to understand state relationships in a gaseous system. For example, in a system of constant temperature and pressure, we know that the addition of more moles of gas results in an increase in volume. Similarly, we can look at a system of constant temperature and moles and see that a decrease in volume results in an increase in pressure.

One challenge is that the ideal gas law describes gases behaving ideally. So what do we mean by that? Ideal behavior assumes that first, the molecules themselves are infinitesimally small and essentially have no volume and that the distance between the molecules is significantly larger than the size of the individual molecule.

Second, we assume that the molecules are constantly in motion. Any collisions occurring between the molecules are elastic, and their motion is frictionless, meaning that the molecules do not lose energy. Finally, we assume that there are no intermolecular forces acting between the molecules and their surroundings.

Unfortunately, most gases do not behave ideally. At very low temperature or high pressure, molecules are very close together and slow-moving, so intermolecular interactions are significant. Similarly, gases with a high molecular weight experience increased interactions due to their large size and mass. However, the ideal gas relationship serves as a good approximation in general.

So how do we use the ideal gas law to study the behavior of a gas in the laboratory? Pressure, volume, and temperature are generally more easily measured, but how about moles, and by extension, mass?

One of the simplest ways to measure the mass of a gas is by the Dumas method. To perform this test, a small amount of a volatile compound in its liquid phase is placed inside a Dumas tube, and the tube is then placed in boiling water.

A volatile compound has a high vapor pressure at room temperature. The vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid phase. Thus, a volatile compound with high vapor pressure transitions from liquid to gas rapidly.

When this happens, the newly formed gas forces the air out of the Dumas tube so that it is solely filled with gas. Once the tube is removed from the water bath and left at room temperature, the gas condenses to form a liquid again. Since mass is conserved, we know that the mass of the condensed liquid is equal to the mass of the gas that filled the known volume of the Dumas tube.

In this lab, you'll explore the ideal gas law by using the Dumas Method to determine the molar mass of an unknown volatile substance. You'll then measure the temperature, pressure, and volume of the system and see how much this gas deviates from ideality.

At the end of this lab, students should know...

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What is a gas?

A gas is a fundamental state of matter that is a collection of molecules with significant distance between them. Gases are highly compressible and are the least dense state of matter.