Hands-on Activity Counting Calories

Learning Objectives

After this activity, students should be able to:

• Describe several basic principles of thermodynamics and heat transfer in action.
• Compare and contrast the differences between real-world application and on-paper analysis.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

For demonstration:

• 2 beakers
• KCl (potassium chloride) salt
• water
• a thin, lightweight piece of wood or 6-8 Popsicle® sticks
• thermometer
• stirring device (such as a Popsicle stick or coffee stirrer)

Each group should have:

• 2-3 Styrofoam® coffee cups
• paper cups
• cloth
• felt
• foam
• thermometer
• one stir rod
• water
• rubber bands
• tape
• paper
• any other materials that may be beneficial for a team's design
• Wait, What Just Happened? Worksheet, one per student
• Your Calorimeter and Your Lab Worksheet, one per student
• Evaluation and Improvement Worksheet, one per student

To share with the entire class:

• scissors
• aluminum foil
• potassium chloride

Worksheets and Attachments

Pre-Req Knowledge

Algebra: Students need to know how to perform basic algebraic manipulation of equations and substitution techniques.

Chemistry: Students should be aware that chemicals interact in reactions that change the chemical and/or physical properties of a system. Also, students should have some experience with mole balances or stoichiometry (the math behind chemistry).

Physical Science: Students should be familiar with concept of energy, that it can be exchanged, and that it comes in different forms.

Introduction/Motivation

Do you ever wonder exactly how it is known how many calories are in a delicious bag of chips? Or how much energy is in a refreshing can of pop? What about chemical reactions like hydrogen and oxygen? It reacts so quickly, how can a scientist or engineer even begin to measure the energy released? How can we scale reactions for different sizes and amounts of the reactants? Many of you might be thinking "Well, they look it up of course!" Ultimately, the data had to come from somewhere. The answer to all these questions is calorimetry. If we react our item of interest in the presence of a substance with a known heat capacity, we can measure the temperature change of the known substance using a calorimeter. Oftentimes, this substance is water. We can then relate the temperature change to the amount of heat transferred using certain equations of heat transfer.

This activity demonstrates not only the heats of solution, but how we measure these values and certain problems we encounter in trying to do this accurately and inexpensively in real-world situations.

Procedure

Background

[For teacher] The Styrofoam cups are good insulators (which is part why we use them for hot coffee). Provide several different materials and cups for the students, and let them decide what would best insulate their reaction. One of the better ways to use Styrofoam cups is to nest them in each other, creating a double layer of insulation. If possible, avoid air space above the water and below the nested cup. A cap is also important to prevent heat escaping into the air. Provide cloth and plastic for use as caps, in addition to regular coffee cup caps. Have students create some variations on this general theme based on their knowledge of calorimeters. More background is provided on the associated pre-worksheet, "Wait, What Just Happened?"

Before the Activity

• Cool two beakers of 100mL of water to just about freezing.
• Gather materials.

With the Students

Part 1: Demo

Cool two beakers of water to just about freezing. Place enough Popsicle® sticks, or the thin piece of wood, on a flat surface, ensuring that the beaker fits on top of the wood/sticks. Pour some of the ice-cold water from the first beaker onto the wood/popsicle-sticks. Place the second beaker on top of the wood, making sure there is water between the wood and glass. In the second beaker, drop a few teaspoons of salt and stir well. Use a thermometer to measure the temperature as it drops below 0°C (or 32°F, the freezing point of water), even though no ice has formed inside the beaker. After a couple minutes of the beaker water being at a temperature below the freezing point of water, lift the beaker off the table. If the demo was successful, the wood should be frozen to the beaker. Ask students how much energy it might take to do this per mole of water. Tell them they need to design a way to measure how much heat is absorbed in dissolving this salt per gram of salt.

Part 2: Designing a Calorimeter

1. After the demonstration, have the students read the Wait, What Just Happened? Worksheet . After they have finished reading the background information, the students should answer the worksheet questions. Next, discuss places where heat can be lost, such as the air, a table or even a calorimeter.
2. Show the class the materials available to them for their calorimeter design.
3. As a class, discuss some of the qualities of the different materials. How is a paper cup different than a foam cup? How is foil different than felt?
4. Divide the students into groups of 2-3 and have them brainstorm ideas for what they think would be the most efficient calorimeter. Have each group design a calorimeter on paper, using the materials at their disposal.
5. Check to make sure the devices are feasible. If they are not, direct students to keep thinking and designing. A feasible device should be able to hold water, and be made of something somewhat insulating. A cup should probably be used in the design. Ensure that each group includes access points for thermometer and stir device. Sign off on feasible designs. See Figure 2 for a sample calorimeter.

   

6. Distribute supplies to each group.
7. As groups complete their design, have them conduct a test to ensure the calorimeter will actually hold water and is more or less insulated. For example, have the students fill their calorimeter with hot water. If they can feel the warmth on the outside, then a design iteration (redesign) should be considered.
8. After everyone has a satisfactory calorimeter, the students should begin to measure the heat of solution of KCl in water. The procedure is explained in the Your Calorimeter and Your Lab Worksheet.
9. After the activity, the students should complete the Evaluation and Enhancement Worksheet.

Vocabulary/Definitions

adiabatic: Does not conduct heat, Q=0. Impermeable to heat

calorimeter: A device designed to measure transferred energy, or heat.

calorimetry: The applied use of a calorimeter.

constant pressure heat capacity : (Cp) The amount of energy required to raise or lower a given amount of a substance by one unit temperature at a constant pressure.

enthalpy: A special value used in engineering to describe the amount of energy in a system including pressure and volume, relative to a reference state.

equilibrate: To go to equilibrium; to come to a balanced, stable state.

heat: Energy transferred between two systems as a result of a temperature difference.

heat of solution: The energy generated or consumed when dissolving one substance in another.

Assessment

Pre-Activity Assessment

Brainstorming: In small groups, have the students engage in open discussion. Remind students that no idea or suggestion is "silly." All ideas should be respectfully heard. Encourage wild ideas and discourage criticism of ideas. Before showing students the available supplies, have students begin to think about how to make a calorimeter the most effectively. Should they use a glass jar vs. a plastic container vs. a paper or foam cup. Give them time to come up with wild ideas as well as feasible ideas so that they begin to think like engineers.

Worksheet: Instruct the students to complete the Wait, What Just What Happened? Worksheet. Review their answers to gauge their mastery of the subject.

Activity Embedded Assessment

Your Calorimeter and You Worksheet: Have the students complete the Your Calorimeter and Your Lab Worksheet. Review their answers to gauge their mastery of the subject.

Post-Activity Assessment

Worksheet: Have the students complete the Evaluation and Improvement Worksheet. Review their answers to gauge their mastery of the subject.

Safety Issues

Students should use gloves and goggles when using the salt. Remind the students not to eat the KCl, and not to rub it in their eyes.

Troubleshooting Tips

The KCl may become lumped together in a large chunk and need to be broken up. To prevent this from happening over and over again, store it in an airtight container in a dry location.

If the calorimeter loses too much heat to surroundings, the temperature might not noticeably change. Try using more salt, ensuring that it is well mixed, and touch the calorimeter as little as possible. Your hands add heat to the system.

Activity Extensions

To add another real-world dimension to the activity, give each group a starting amount of fake money (for example, Thermodollars) and require them to "buy" each item. This puts some constraints on their designs, such as only being able to afford two cups and one piece of foil instead of three cups and unlimited foil.

Activity Scaling

• For lower grades, provide a standard plan for the calorimeter to test the same reaction.
• For upper grades, the students should talk to local college/university professors about getting the opportunity to work in the lab and use actual calorimeters for chemical reactions.

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.