Summary

In this lesson, students will investigate relationships of variables involved with gases. They will draw pictures and explain in words what they observe and why.

Grade Level

High school

Objectives

By the end of this lesson, students should be able to

• Understand the relationship between temperature and volume of a gas at constant pressure.
• Understand the relationship between temperature and pressure of a gas at constant volume.
• Understand the relationship between pressure and volume of a gas at constant temperature.

Chemistry Topics

This lesson supports students’ understanding of

• Gases
• Gas laws
• Temperature, pressure, and volume relationships

Time

Teacher Preparation: 20 minutes

Lesson: one class period

Materials

Chillin’ and Heatin’ (temperature and volume)

• Sealed syringe
• Ice water bath
• Thermometer
• Hot water bath

The Steak Bottle and the Dime (temperature and pressure)

• A-1 Steak Sauce bottle (empty)
• Dime
• Ice water bath

The Distortion of Marshmallows (pressure and volume)

• Mini marshmallows
• Pen
• Syringe

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials.
• Food in the lab should be considered a chemical not for consumption.

Teacher Notes

• This lab is suggested as day one of a seven day gas law unit. See the full article in the March issue of Chemistry Solutions for the other parts of the unit.
• You could return to the (optional) data collected in the Chillin’ and Heatin’ (station 1) to have students verify Charles Law. You could have them also take measurements at room temperature and then graph T vs. V, T vs. 1/V, and T vs. V² to find the linear relationship.
• In “Chillin’ and Heatin’,” students work with a sealed, variable volume syringe at two temperatures. For the purposes of this investigation, the actual temperatures are not important; they need to recognize only that one temperature is higher than the other. They should note that as temperature increases, the volume of the gas also increases, because the average velocities of the air molecules increase. Students need to understand that the pressure didn’t change, it is room pressure. They also need to know that the amount of air inside was constant.
• In “The Steak Bottle and the Dime,” students use their hands to warm a chilled bottle that has a dime acting as a kind of valve. I use a dime because it exactly fits over an A-1 Steak Sauce bottle and the dime itself has a low mass. That means as air molecules attain a higher average speed, some will escape the bottle and cause the dime to move as they do so. Pressure is constant (room pressure) so as the molecules speed up, fewer can fit in the constant volume bottle.
• In “Distortion of Marshmallows,” students discover that as they increase the volume of a sealed syringe, air molecules in the marshmallow inside the syringe are able to occupy a larger volume. The total volume of air in the syringe, and the internal marshmallow, increases as pressure goes down. This cycle of expansion is followed by a compression, during which the marshmallow shrinks because the air molecules are confined to a smaller space at higher pressure. (Ultimately the marshmallow fails because of the attraction of the molecules of the marshmallow for each other and the irreversible escape of the last of the gas inside the marshmallow.)