Students observe and describe changes to objects. They also consider how changes may be caused by heating or cooling an object and that changes may be reversed, while at other times changes cannot be reversed.

Show the students a piece of bread and ask them to make observations about the single piece of bread. Observations will be largely qualitative, such as color, smell, and shape but can also be quantitative at this level if the teacher has students measure the size of the piece of bread. The teacher should record this information on the board. Pose the question to the students: How could I change this piece of bread? Can this change be undone or reversed, so it is still the same piece of bread? As students offer answers, prompt further by asking Can you think of a change that can’t be undone or reversed?

Now share Do You Really Want to Burn Your Toast?: A Book About Heat by reading it all the way through to the students the first time. At the end of the reading, ask the following questions: What was the story about? How do you think this story connects to the topic of changes?

Explain to the students that this story connects to changes that happen and that they will be participating in several different lessons over the next few days. Each of the following demonstrations can be done as a full class demonstration with students participating as appropriate. At the beginning of each activity, refresh the idea that students are looking for changes to the objects; if the change can be reversed or undone, and where or how heat helps make those changes. (Safety note: Remind students that they should not put anything in their mouth during science activities. Additionally, teachers should verify whether students have allergies to the items used in these demonstrations ahead of time).

Provide a small bag of Skittles and a small bag of M&M’s for each table along with a plastic container. Ask the students to first open the M&M’s and make observations and then the Skittles on their What Is Happening Change Sheet (see NSTA Connection). Have the students pour the two different candies into the plastic container and mix them up. Now make observations. Questions to help prompt the students include: Can you separate the candies out again into their own piles? Did the candies change their shape or form? Did the candies change into something new? Was heat added or taken away at any point? If your school has a “no food” policy, you could substitute green and red marbles for the M&M’s and skittles.

Give each student a sheet of white paper and then ask them to tear it up or shred it into smaller pieces. Ask them to make observations about the piece of paper before and after they shred it. Questions to prompt student’s discussion include: After you shredded the piece of paper, was it still paper? Could you reassemble it to its original shape? Students will often say yes if they put the pieces together, but they would need to either tape it or find another way to reassemble the pieces, which is still a change from the original piece and shape. Other examples of physical changes that are not reversible include peeling an orange or cutting your hair.

Demonstrate a physical change for students by making a sandwich with two pieces of bread and a piece of bologna. Assemble the sandwich for the students and ask them if it is possible to undo this sandwich in a similar way to sorting the skittles and M&M’s in the first demonstration. Then cut the sandwich in half and ask the students if it is still possible to undo or separate the parts of the sandwich? Has the bread changed? If so, how? Is it still bread or has it changed into a new substance?

After these three demonstrations, discuss that each of these represented a physical change which means the objects or substances may change their shape or form, but are still the same object. An option for this if you choose not to use food would be to cut out bread and bologna from either cardboard or Styrofoam ahead of time to use.

Demonstrate how to make toast with a toaster, similar to what the children did in the story. Prompt the students with questions such as “How did the heat change the bread? What observations can you make? Is it possible to change the toast back to bread?” An alternate option would be to video the idea of making toast and share the video to allow students to make observations.

Using a standard muffin mix, demonstrate for the class or allow the different tables of students to make their own muffins with adult supervision. Show students the individual components of the muffin mix (for example, oil, water, and eggs) to help them understand the concept of mixtures. Allow the students to observe the muffin mix before it is baked and after the muffins are removed from the oven, and record their observations on their student sheet. Use of a video would work or perhaps asking your food service staff to assist so that the muffins are prepared in the kitchen.

Show the students baking soda and vinegar and then mix the ingredients together in a beaker with one teaspoon of baking soda and two teaspoons of vinegar. What do they observe when the two are mixed? Can the mixing of these two items be undone or reversed?

After these three demonstrations, discuss that each of these represented a chemical change, meaning the objects or substances were changed into something new. Also discuss that when this type of change happened, heat was part of what caused the change.

Help students understand each of these ideas by discussing the ideas and adding the proper terminology to what is happening in each demonstration. The ideas are physical change, chemical change, reversible, irreversible.

Return to the following pages in Do You Really Want to Burn Your Toast? and connect the story to the concepts related to heat and change. Tell the students that they are going to discuss parts of the story and they should think about where heat was used and what kind of change happened.

• p. 4: When the children decide to cook food for their parents, they state that they will need heat to do so. What is heat?
• p. 7: What happened when too much heat was used to toast the bread? What observations can you make about the change from the bread to the toast? Could they change the toast back to bread?
• p. 12: We used different ingredients in the muffin mix, such as eggs, flour, baking soda, and blueberries. Each of these ingredients were mixed together. What happens to the muffin batter as it is heated? Can this change be undone or reversed?
• p. 15: If the butter warmed up when taken out of the fridge, what change happened to it (physical or chemical)? What would happen if you were to put the warm butter back into the fridge? Why is this a physical change?
• p. 20: In the story, the young girl cooks the eggs and makes scrambled eggs. Explain how the eggs were changed by adding heat to them while they were in the pan.

Using the Changes Cards (see Supplemental Resources) that are provided, ask the students to sort the cards into the different categories to demonstrate their understanding of physical versus chemical changes and also their understanding of when heating or cooling has been part of the change and if something is reversible or not. It is important to realize that we are asking students at this age to demonstrate an understanding of each idea and not to be able to combine all of the ideas together. Provide the card set to each student or pair of students and ask them to complete the following tasks.

• Can you separate the cards into the changes that cause the object to change shape or form or change the original substances into a new substance?
• Can you pull out the cards that show situations where heating or cooling helped make the change?
• Can you separate the cards into two categories that show what changes can be undone and what ones can’t be undone?

This topic in physical science is challenging for students and needs explicit examples to help them understand and connect the concepts. Students’ initial understanding is assessed when they are asked to describe what is happening to a piece of bread and how the bread might be changed. As students are participating in the demonstrations, they are making observations about changes that happen and also starting to identify if heat helps make the change that connects to the disciplinary core idea. Finally, students are asked to sort images based on characteristics discussed in this lesson including physical and chemical changes, reversible and irreversible changes, and changes that involved heating and cooling.

Students explore what happens to mass during situations that involve different physical and chemical changes.

Provide some context for the students about the story that they are going to hear. Specifically, tell students that Michael Faraday was a scientist who lived in England in the mid1800s. During that time, lectures or presentations were given at the holidays and his lecture encouraged kids to really observe a candle and determine how it burned. This is a retelling of his lecture for students in the form of a picture book. Now that students have been provided some context, read the story Burn: Michael Faraday’s Candle to the students and discuss the following points:

• p. 7–8: How did Michael Faraday describe the candle that he was using in his demonstration? What were the candles made from?
• p. 11–12: Look closely at the diagram of the candle when it is lit. What are some of the key parts of the candle? What is happening when it is lit? How did the shape help the candle burn?
• p. 15–18: When fuel is carried to the part of the candle where burning happens, what is that action called?
• Ask the students to consider what type of changes happen with the burning of a candle and explain why. If necessary, review what happens in a physical change and chemical change. Burning a candle produces both a physical change: the wax melting and then hardening again and also a chemical change. The chemical change happens where some of the wax vapor burns since it produces carbon soot, water vapor, and carbon dioxide. Challenging students to think about where and how physical and chemical changes happen begins to engage their understanding about changes in substances. Pose the following question to the students and ask them to discuss their initial ideas. If we were to measure the mass of the candle before burning it and again after burning it, what do you think you would notice? Now, what do you think would happen if we could collect every product (the carbon dioxide, the water vapor, and the soot) as the candle burned and determined the mass of everything combined? Allow the students to consider this aspect and record questions they have on chart paper.

Outline for the students that they are going to participate in several different stations where they are determining what happens to the mass of matter (any object) when changes happen.

Have a station where students can put on a variety of different types of clothes over their own clothes and then determine their mass on a scale (an electronic scale works best). Ask students to record this information on their Its Mass is What? student data sheet (see NSTA Connection). Then ask the students to remove their clothes and determine both their own mass and the mass of their individual clothes. Have the students note that the mass should be the same when they are wearing the clothes and when the clothes and their mass are determined separately and then added together. Engage them in a discussion about what type of change (physical or chemical) this is and why.

Determine the individual mass of one cup of sand and one cup of gravel (make sure you are only finding the mass of the sand or gravel and not the container that it is placed in as well). Record this information on their student data sheet. Now, mix the sand and gravel together and determine how much it weighs (again taking care not the include the mass of the container). Would this be a physical or chemical change and why?

Have students measure the mass of a glass of warm water by using a balance and record the information. Then ask the students to pick up a premeasured amount of salt (such as 100 grams) and slowly mix the salt into the water until it dissolves. After the salt has dissolved, ask the students to determine the mass of the cup with the water and now dissolved salt again. Ask them what they notice about the first two masses when they add it together and compare it to the mass of the glass with both the water and salt. Some students may be off by a few grams and this can be explained by a balance not being precisely calibrated.

Place three cups of Kool-Aid or juice into a sealable bag and seal it. Ask students to measure the mass of the bag with the liquid and record the information. Now have the students place the bag, which should be labeled with the group’s name, into the freezer and allow it to freeze overnight. Remeasure the mass of the bag and compare the measurement to the first measurement. What happened to the liquid? What type of change was this?

Up to this point, the different stations have involved physical changes. No new substances were created although the shape or form of some substances occurred. In this station, students will be examining what happens in a chemical change. Safety note: Chemical splash goggles and gloves are necessary. Provide each group with two tablespoons of baking soda wrapped in tissue paper, a small paper cup filled half-way with vinegar, and a sealable bag. Ask the students to place the bag on the balance, then carefully place the tissue paper with baking soda inside, and then put the cup of vinegar inside the bag without spilling it. Have students remove as much air as possible as they seal the bag carefully. Determine the mass of the bag and its contents. Remind the students that they will NOT open the bag again and should make sure that it is sealed. Once they have recorded the mass, ask them to tip the bag sideways so that the vinegar mixes with the baking soda in the tissue paper. Make observations about what is happening. After five minutes, remeasure the mass of the bag with its contents and compare that number to the original number. Again, it may be off by a few grams but that could be due to a leaky bag or the balance.

Once students have had a chance to participate in the different stations, draw them back together for a group discussion. Using the following questions to guide the conversation, have students report on their findings and observations, and eventually help them draw a conclusion about what happens to mass at these stations.

• Which of the stations represented a physical change and which represented a chemical change? What is the difference between the two types of change?
• What did you notice about the mass of the clothes when you wore them and when you measured the mass of the clothes you added and your mass separately? How does this model a physical change?
• If a physical change means that no new substance is created but the shape or form of the object might change, which stations gave an example of this happening?
• Explain why each of the stations with the clothes, the sand and gravel, the dissolving salt, and the state changes demonstrated a physical change? Which one involves a change of state as well?
• When you mixed the baking soda and vinegar, something else was created in the reaction: What was it? Why was it important to keep the bag sealed so that the gas was trapped inside of the bag? Do you think the gas created had mass? Why or why not?
• Why was mixing the baking soda and vinegar an example of a chemical change?
• Which stations demonstrated heating, cooling, or mixing substances?

Ask the students to conduct the following investigations.

Alka-Seltzer and Water: Using a similar method that they did for the vinegar and baking soda, ask students to chop up half an Alka-Seltzer tablet and place it in a sealable bag. After placing a small paper cup full of water in the bag, sealing it and determining its mass, have the students develop a picture or sketch of what happens to include labeling the picture. At the bottom of their picture, ask them to explain if it is a chemical or physical change and why, as well as their understanding of what happened with the mass.

Trail Mix: Provide each group with one cup each of M&M’s, nuts (check for allergies), dried fruit, and sunflower seeds and allow them to create trail mix. Once again have the students determine the mass of the individual components first and then the mass of the trail mix. Have students develop a picture or sketch of what happens to include labeling the picture. At the bottom of their picture, ask them to explain if it is a chemical or physical change and why as well as their understanding of what happened with the mass. (Safety note: Remind students not to eat anything during class.)

Students are asked to first describe their understanding of properties of matter as they listen to the story about Michael Faraday’s lecture and also the difference between physical and chemical changes. Throughout the explore stations, they are examining that mass does not change during a physical or chemical change in a closed system and then explaining their understanding during the explain and elaborate steps where they are labeling and diagraming what is happening and explaining their thinking.