Summary

In this demonstration, students will explore how changes in pressure and temperature affect the solubility of a gas in an aqueous solution. In addition, students will have the opportunity in a post-demonstration reflection activity to practice using data (in this case their demonstration observations) to make evidence based claims.

Grade Level

High School

NGSS Alignment

This demonstration will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.
• HS-PS1-4: Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.
• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data
  • Engaging in Argument from Evidence

Objectives

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

• Describe how changes in temperature affect the solubility of gases in aqueous solutions.
• Describe how changes in pressure affect the solubility of gases in aqueous solutions.
• Predict how a specific change in temperature or pressure would change the amount of gas dissolved in an aqueous solution.

Chemistry Topics

This demonstration supports students’ understanding of

• Solutions
• Gases
• Solubility
• Concentration
• Temperature
• Pressure

Time

Teacher Preparation: 15-20 minutes

Lesson: 30 minutes

Materials

Demo #1: Gas solubility and temperature

• Large bolt, drill bit or other piece of metal
• Bunsen burner (or other means to heat the piece of metal)
• One unopened 12 oz. bottle of soda
• Tongs
• Demonstration tray or large plastic bin

Demo #2: Gas solubility and pressure

• One unopened 12 oz. bottle of soda
• Two 250 mL Erlenmeyer flasks
• Vacuum pump with bell jar
  Post Demo analysis:
• Access to the Internet or some other means to conduct follow up research on the solubility of oxygen and nitrogen in water.

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Always use caution around open flames. Keep flames away from flammable substances.
• Always be aware of an open flame. Do not reach over it, tie back hair, and secure loose clothing.
• Open flames can cause burns.
• An operational fire extinguisher should be in the classroom.
• Do not consume lab solutions, even if they’re otherwise edible products.
• Food in the lab should be considered a chemical not for consumption.
• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.

Teacher Notes

• Prior to engaging in this activity, students should have discussed the basic concepts of temperature, pressure, concentration and solubility.
• This activity is intended to allow students to “discover” how changes in temperature and pressure affect gas solubility. Due to this, these concepts should not be discussed before engaging in this activity.
• In part I, the soda should fizz to the point of overflowing once the piece of hot metal is placed in the bottle so it should be conducted on a demonstration tray or plastic bin (see photo included in the instructions).
• While the teacher instructions contain general guidelines, prior to conducting the demonstration, the teacher should practice to determine if any alterations are needed for the length of time required to heat the metal piece in part I since it will vary depending on the size of the metal piece.
• In part II, the goal is to reduce the pressure enough for the gas to leave the solution but not so much so that the solution begins to boil. (see photo included in the instructions)
• While the teacher instructions contain general guidelines, prior to conducting the demonstration, the teacher should practice to determine if any alterations are needed for the length of time required for the soda to be evacuated bell jar in part II since it will vary depending on the specific evacuation setup (type of vacuum pump, bell jar etc.).
• As written, the brief pre-demonstration questions are assigned as homework the day before the demonstration is performed. Prior to the demonstration students will briefly share their responses in a whole class discussion. If desired, the questions can be introduced the day of the demonstration and discussed either in small groups or in a whole-class discussion.
• Prior to beginning the activity, students should be reminded to record detailed observations of both parts of the demonstration in the tables provided. They will be using their observations in a post-demonstration reflection.
• Prior to each part of the demonstration, students will be asked to individually predict the impact of the change on the solubility of the carbon dioxide in the soda (increasing the temperature in part I and decreasing the pressure in part II). These predictions should be recorded in the tables provided (or a lab notebook). If desired, the teacher can solicit predictions from the class prior to starting the demonstration.
• After both parts of the demonstration, students will form small groups (2-3 students per group) and briefly discuss (5 minutes or so) what they observed and what is suggests about how changes in temperature and pressure affect the solubility of carbon dioxide in water.
• As a culminating part of the activity, students will complete the post-demonstration analysis questions. As written, these are to be completed by students individually in class but they can also be assigned as homework or completed in small groups.
• The post-demonstration reflection asks students to research the solubility behavior of oxygen and nitrogen gas in water at different temperatures and pressures. As written this requires access to the Internet or some other source. If desired, teachers can provide this information for students.
• Answer key for the analysis section has been included as a separate document available to download.

Teacher instructions to conduct the demonstration:

Part I: Effect of Temperature

1. Put on goggles and apron.
2. Open the 12 oz. bottle of soda and place it on the demonstration tray.
3. Light a Bunsen burner or other flame heat source.
4. Using the tongs, hold the piece of metal^* in the flame for about 2-3 minutes. Move the metal around in the flame to insure even heating.
5. Drop the hot piece of metal into the soda. Result: The soda will fizz and overflow as shown in the photo:

*NOTE: You can use any piece of metal as long as it will fit in the neck of the bottle. Two options that worked successfully for me were a drill bit (left), approximately 11cm in length, and a small bolt (right), approximately 7cm in length.

Part II: Effect of Pressure

1. Setup vacuum pump with bell jar.
2. Open a 12 oz. bottle of soda.
3. Add approximately 50-75 mL of soda to two 250 mL Erlenmeyer flasks.
4. Place one on the bench (this is the control) and the other inside the bell jar.
5. Turn on the pump to reduce the pressure inside the bell jar. Result: As shown in the photo, almost immediately, the soda will start to bubble and fizz.