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 of melting and freezing 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 a substance that can be a solid or a liquid.

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 remove the chocolate.
• If you are using thermometers with a paper backing, you will use a separate thermometers for the room-temperature and frozen chocolate. This makes your measurement more accurate since the chocolate can be difficult to clean off 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 by going over the basic information below:
   
   Depending on your student’s knowledge and experience, you could teach this as new information or as review.
   
   All matter on Earth is made up of extremely tiny particles called atoms and molecules. At normal temperatures, these atoms and molecules are arranged as a solid, liquid, or gas. These three characteristics or “states” of being a solid, liquid, or gas are called the “states of matter”.

• In a solid, molecules are strongly attracted to one another and vibrate but do not move past one another. They stay in fixed positions because of their strong attractions for one another. A solid has a definite volume and a definite shape.

• In a liquid, molecules are attracted to one another but are able to move past one another. A liquid has a definite volume but does not have a definite shape.

• In a gas, molecules are not attracted to each other much at all. The molecules in gas move freely past each other. A gas does not have a definite shape of volume. Gas molecules will spread out evenly to fill any container.
  
  

2. Introduce the main idea of melting chocolate from a solid to a liquid

• 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.
• 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.
• 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?

3. Complete the demonstration (instructions below).

• Instruct students to complete the analysis and conclusion parts of the student activity.
• [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 the 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 frozen.

Expected Results:

• It should take the room-temperature chocolate approximately 1 minute to melt in the microwave (don’t forget to stir periodically!)
• It should take the frozen chocolate about 2 ½ minutes 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).