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?

5. Complete the demonstration (instructions below).
6. Instruct students to complete the analysis and conclusion parts of the student activity.
7. [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).