Summary

In this lesson, students will use volcanoes as a vehicle to learn about the differences between endothermic and exothermic reactions by completing a hands-on activities and observing a teacher-led demonstration.

Grade Level

Middle School

NGSS Alignment

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

• MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
• MS-PS1-5: Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.
• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking
  • Analyzing and Interpreting Data
  • Engaging in Argument from Evidence

Objectives

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

• List indications of chemical change.
• Explain the difference between endothermic reactions and exothermic reactions.

Chemistry Topics

This lesson supports students’ understanding of

• Chemical Reactions
• Chemical Change
• Indicators of a Chemical Reaction
• Endothermic Reactions
• Exothermic Reactions
• Observations

Time

Teacher Preparation: 15-30 minutes (depends on if using lab stations or a teacher demonstration)
Lesson:
Part 1: Accessing Prior Knowledge – 20 minutes
Part 2: Exploring Reactions – 45 minutes
Part 3: Explaining Reactions – 30 minutes

Materials

Activating Prior Knowledge – Teacher Demo

• Play-dough/clay, 8 oz. water bottle (to create a volcano structure)
• Baking soda (2 tbsp.)
• Vinegar (1/4 cup or approx. 60 ml)

Activity 1 (Student lab activity): Baking Soda and Vinegar (per group)

• Student handout
• 10 g Baking soda
• 10 mL Vinegar
• 10 mL Graduated cylinder
• Thermometer
  • Infrared thermometers and temperature probes provide more precise data than glass thermometers for this activity. Your school custodial staff may have an infrared thermometer you can borrow.
• 100 mL Beakers
• Balance
• Timer

Activity 2 (Teacher Demo): Giant Toothpaste

• 118 mL (half a cup) 3% Hydrogen Peroxide
• 1 active dry yeast packet (1/4 oz) dissolved in 3 tbsp warm water
• Erlenmeyer Flask
  • 250 mL or larger to conduct the reaction. A 12 oz plastic bottle will also work.
• 3 tbsp Water
• Clear dish soap
• Funnel

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals. Solid materials can be placed in the trash while liquids should be flushed down the sink with ample amounts of water.
• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.

Teacher Notes

• The amount of materials needed will vary depending on whether the teachers conducts the chemical reactions as demonstrations or as hands on activities with student groups.

Part 1: Accessing Prior Knowledge

• Prior to this lesson students should understand the difference between physical and chemical changes as well as the indicators of a chemical change.
• The teacher will begin the lesson by showing a video clip of volcanic explosions.
• After playing the clip, the teacher will ask the students what they noticed and have them write the information on their student page. Students should notice that gas and lava come out of the volcanoes.
• The teacher will ask the students if they know how they know how to use chemistry to make a volcano.
• The teacher will then conduct a baking soda and vinegar volcano demonstration. The volcano can be made of play-doh, an 8oz plastic water bottle, or other similar container. The baking soda (2 tbsp) should already be inside the volcano and the teacher should ask the students to observe what happens as the vinegar is poured into the volcano. The students and the teacher should be wearing aprons and goggles during the demonstration.
• If time and materials are a factor, the teacher may decide to use a video (such as the first five seconds of this video) of a baking soda and vinegar volcano.
• The teacher will ask the students what they noticed during the demonstration and how that compared with what they noticed in the video of the volcano. Students should identify that they saw bubbles or foam come out of the top of the volcano after the liquid was added.
• The teacher will ask the students how the real volcano and the chemistry volcano might be different. Students may volunteer to answer and then the teacher will explain that answering the question may take some more investigating, necessitating the rest of the lesson)
• The teacher will ask the students how they think the chemistry volcano worked. After taking volunteer answers, the teacher will explain that the volcano demonstration was a chemical reaction.
• It may be necessary to remind students that common signs of a chemical reaction include: the production of a gas, the production of a precipitate, an unpredictable change in temperature and an unpredictable change in color. Emphasizing the unpredictability of temperature and color change in chemical reactions can help alleviate potential misconceptions between physical and chemical change in a variety of situations such as why soda cools down when ice is place in it or why water may change color when a substance like Kool-Aid is added.
• The teacher should explain that the class will be exploring two chemical reactions that may look like volcanoes in order to compare and contrast them to one another as well as to real volcanoes.
• The teacher will explain that while they will not be able to gather data on real volcanoes, the students will be observing two different chemical reactions that look a bit like volcanoes.
• The teacher will ask the students what type of qualitative and quantitative data they could collect when they make observations to assist them in making these comparisons. The students should identify that they can collect information about mass, temperature, state of matter, and color.

Part 2: Exploring Reactions

• The teacher will explain that the students will use what they have learned so far to observe two chemical reactions.
• The teacher will ask students to predict what will happen when they add vinegar to baking soda. Many students have experienced this reaction before, so they should be able to identify that the reaction will bubble. Many students may not realize that the temperature will drop. At this point it is important to remind the students that they need to make very careful observations as the chemical reaction takes place.
• The students should be placed in small groups of three or four students and asked to conduct the baking soda and vinegar portion of the activity. They should wear proper safety gear and be monitored closely ensure both safety and that they are recording data on their data tables.
• The box of baking soda and bottle of vinegar can be placed in a central location so the student groups can access the materials as this is an opportunity for students to practice their measurement skills. If time is a factor, the teacher can pre-measure the items and place them at each lab station.
• Students should be reminded to take the temperatures of the reactants before they conduct the reaction and then to place the thermometer in the beaker to measure the temperature while the reaction takes place.
• If time is an issue, the baking soda and vinegar activity can be completed as a demonstration.
• After the students have cleaned up their work areas, the teacher should announce that the second reaction will be conducted.
• It is recommended that the Giant Toothpaste activity be conducted as a teacher demonstration. Students still need to wear their personal protective equipment.
• The teacher should work through the Giant Toothpaste demonstration step-by-step, explaining the chemicals involved and allowing time for students to make observations to complete their data charts. For instance, when the teacher dissolves the yeast into the water, they should show the students that the yeast is dissolved. The teacher should collect the temperature data of the reactants prior to the reaction and then monitor the temperature for the duration of the reaction. This can be done by placing a thermometer or temperature probe in the reaction flask and checking the temperature every ten seconds during the reaction.
  • Giant Toothpaste Instructions

• Measure 1/2 cup of 3% hydrogen peroxide.
• Use the funnel to pour the hydrogen peroxide into the flask.
• Add a few drops of dish soap to the bottle.
• In a beaker, mix 1 package of dry yeast and 3 tbsp of warm water.
• Stir the yeast and water.
• Use the funnel to pour the yeast and water into the flask.
• Quickly remove the funnel.

• This reaction gets warm and rises quickly. Be ready to move back quickly after pouring the reactants. This can make checking the temperature with a traditional liquid thermometer very difficult. When using a liquid thermometer, it is most practical to take the temperature of the reactants and then check the temperature of the products once the foaming process has slowed.
• Please view the recording of the reaction and conduct a practice reaction prior to using the demonstration in class.
• This reaction is messy, so placing the flask in a tray or having paper towels handy may be helpful.

Part 3: Explaining Reactions

• The teacher should begin by leading a whole class discussion of the similarities between the two chemical reactions. The students should be able to identify that gas was produced as part of the reactions and that both reactions included liquids and solids (baking soda and yeast).
• From there the teacher should have the students focus on the differences between the two reactions, with an emphasis on the difference in temperature between the two reactions.
• Based on the quality of the temperature data collected, the teacher should ask the students to draw a line that represents the temperature before and during each reaction, for instance a line that goes up or a line that goes down, or a more specific line graph to represent what happened to the temperatures during each of the reactions. If possible, the teacher could perform both reactions as a demonstration again, this time with students collecting temperature data every ten seconds in order to create an accurate line graph.
• The students should be able to identify that the line for the giant toothpaste reaction goes up while the line for the baking soda and vinegar reaction goes down.
• The teacher should build on this observation by asking students to think about why one line went up but the other line went down. The students should share their thoughts with the class.
• The teacher should ask the students to think more closely about temperature and remind them that temperature is the measure of the average kinetic energy of the molecules.
• Based on this new information the teacher will ask the students to explain what is happening to the energy in the molecules of the reactants during the reaction. The teacher will also ask them to explain why the energy might be changing.
• After listening to student ideas, the teacher should explain that when some reactions take place energy can be released in the form of heat, so some reactions get hot while other reactions use energy in the form of heat, so they get cold.
• The teacher should introduce the vocabulary terms endothermic and exothermic and ask the students which term describes each reaction.
• Students should be encouraged to work with neighbors to discuss which reaction was endothermic and which one was exothermic, while using evidence and reasoning to justify their ideas.
• The teacher will ask for volunteers to share their responses before explaining that the giant toothpaste reaction was exothermic, and the baking soda and vinegar reaction was endothermic.
• The teacher could also share this online interactive as a visual representation of the energy levels in endothermic and exothermic reactions.
• To conclude the lesson, the teacher should ask the students to use the newly collected data to compare and contrast the chemical volcanoes with the volcanoes they saw in the video.