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Chocolate Changes (0 Favorites)

LESSON PLAN in Melting Point, Phase Changes, Heat. Last updated February 4, 2019.


Summary

In this lesson, students will review what they know about the three states of matter (solid, liquid, and gas). They will perform a word sort about states of matter and discuss how substances can exist in more than one state of matter. Following this they will contribute to a KWL (Know, Want to know, Learned) chart. The teacher will conclude the lesson with a demonstration using chocolate.

Grade Level

Elementary School

NGSS Alignment

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

  • 5-PS1-2: Measure and graph quantities to provide evidence that regardless of the type of change that occurs when heating, cooling, or mixing substances, the total weight of matter is conserved.
  • 5-PS1-3: Make observation and measurements to identify materials based on their properties.
  • Scientific and Engineering Practices:
    • Analyzing and Interpreting Data

Objectives

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

  • Identify the three states of matter and provide examples of each state.
  • Identify chocolate as an object that can be a solid or a liquid.
  • Compare the melting point of chocolate and water.

Chemistry Topics

This lesson supports students’ understanding of

  • States of Matter
  • Phase Changes
  • Melting Point
  • Energy
  • Heat

Time

Teacher Preparation: 15 minutes

Lesson: 30-45 minutes (allow additional time for chocolate to harden)

Materials

  • Student Handouts
    • Student activity sheet
    • Student KWL sheet
    • Student Word Sort
  • Semisweet Chocolate Chips (one standard 12oz package with ½ of the chips at room temperature and ½ of the chips frozen)
  • Thermometer
  • Plastic Spoon
  • Microwave-Safe Bowl
  • Water
  • Ziploc Sandwich Bag
  • Ice Cube Tray or Chocolate Mold
  • Scissors
  • Glue

Safety

  • Students should wash their hands thoroughly before leaving the lab.
  • Food in the lab should be considered a chemical not for consumption.
  • Liquid chocolate is hot and can burn the skin.
  • Exercise caution when using melted chocolate. Students should not touch bowl with chocolate.

Teacher Notes

  • Silicon ice cube trays/candy molds are recommended. They make clean-up faster and are easier than plastic trays to get the chocolate out of.
  • If you are using thermometers with a paper backing, you will want to have a separate thermometer for the room-temperature and frozen chocolate. This makes your measurement more accurate since the chocolate can be difficult to clean off of the paper backing.
  • If you are using a large ice cube tray, a plate and knife may be helpful for cutting chocolate into smaller pieces.

Before the Lesson:

  • Pour half of the chocolate chips in a Ziploc bag and place in the freezer for a couple of hours, or overnight.

Lesson Procedure:

  1. Review the states of matter and have students complete the word sort (see student worksheet) or complete as a class on the board.
  2. Have students do a Think-Pair-Share with a partner and discuss how water and chocolate are similar, and how they can fall under more than one state of matter category.
  3. Ask students if chocolate is normally in a solid or liquid state. Have students give examples of when it can be liquid.After the discussion, tell students that today we will be changing chocolate from a solid to a liquid and then from a liquid to a solid.
  4. On chart paper, create a KWL chart about melting chocolate. Ask students what they already know and add it to the first column of the chart.Then create a list of things they want to know in the second column of the chart.
  • Possible examples for What I KNOW:chocolate can melt in a car, chocolate can melt in my pocket, chocolate milk has liquid chocolate, etc.
  • Possible examples for What I WANT to Know: How hot does it have to be to melt chocolate? How can you make chocolate into a solid again?
  1. Complete the demonstration (instructions below).
  2. Instruct students to complete the analysis and conclusion parts of the student activity.
  3. [Optional] Ask students if chocolate can exist as a gas. The typical answer is no. However, world-class chef Grant Achatz and his famous edible balloons may disagree.
  • This article explains that Grant Achatz made “an entirely edible balloon made from green apple taffy and inflated with apple-scented helium.”
    • Although this isn’t quite the same as a food existing as a gas, it is pretty close.
  • This video shows Grant Achatz making the edible balloons.
  • More detail and clips can be shown from Netflix’s Chef’s Table show, season 2 episode 1.
  • Ask students if they think something similar can be done with chocolate. You may also have them come up with creative ways to make a potential chocolate gas.

Demonstration:

  1. Put the room-temperature chocolate chips a microwave-safe bowl.
  2. Melt the room-temperature chocolate chips, stirring every 15-20 seconds to avoid overheating and to create a smooth consistency.
  3. Once the chocolate is melted and in a liquid form, use a thermometer to read the temperature. Be sure to keep thermometer in the middle of chocolate.
  4. Repeat steps 2-4 with the frozen chocolate chips.
  5. Ask students if it is possible to put the chocolate back into a solid form.
  6. After the discussion, spoon the melted chocolate into the ice cube tray and place it in a freezer or refrigerator (this will take 30-45 minutes).
  7. After the chocolate has frozen, remove it from the ice cube tray. Ask the students if they can see a difference between the chocolate that was originally room-temperature and the chocolate that was originally frozen.

Expected Results:

  • It should take the room-temperature chocolate approximately 1 minute total to melt in the microwave (don’t forget to stir periodically!)
  • It should take the frozen chocolate about 2 ½ minutes total to melt in the microwave.
  • It should take the melted chocolate 30-45 minutes to become solid in the freezer.
  • The temperature of the melted chocolate should be around 94 or 96 degrees Fahrenheit (34-36 degrees Celsius).

For the Student

Lesson

Background

During this lesson, you will sort items according to their appropriate state of matter, and paste them into their proper category: solid, liquid, or gas. You will also take a close look at chocolate, which is normally a solid, but can also be a liquid.

Pre-lab Questions

These questions will be discussed with a partner, and then as a class.

  1. What is a state of matter?
  2. How can some substances change states of matter?
  3. What is a melting point?

Safety

  • Wash your hands thoroughly before leaving the lab.
  • Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.

Procedure

  1. Complete the word sort by cutting out the items and gluing them into the appropriate category.
  2. Complete the Know and Want to Know columns of the KWL chart.
  3. Watch the teacher demonstration and discuss observations on the melting chocolate.
    1. Record the time it took the room-temperature and frozen chocolate to melt in the table below.
    2. After the chocolate has melted record the temperature of the chocolate in the same table.
    3. Record what you learned in the L column of the KWL Chart.
  4. Complete the analysis and conclusion questions.

Results

Minutes to Change From a Solid to a Liquid Temperature Measured After Melting Notes/Observations
Room-Temperature Chocolate
Frozen Chocolate

Analysis

  1. Why do you think we need to stir the chocolate as it melts?
  2. How is chocolate changing states similar and/or different from how water changes states?
  3. In this demonstration, chocolate chips were melted. How do you think the outcome would be different if we used a large chocolate bar instead?

Conclusion

Based on your observations, what did you learn about how chocolate changes states?
In a few sentences, explain how chocolate can change state and what states it can exist in. Be sure to include data from the results table in your explanation.