Physical Changes Versus Chemical Changes
Lesson 6 of 10
Objective: SWBAT determine if changes in matter have created something new or not.
The Why Behind Teaching This:
Unit 2 addresses standards related to matter and it's interactions. The unit begins with identifying types of matter and the particles that make it up. This is covered in standard 5-PS1-1: Developing a model to describe that matter is made of particles too small to be seen. We will be changing matter by melting, evaporating, and dissolving to prove that although the physical appearance has changed, the same amount of matter still exists. This is covered in standard 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. We will also be using a variety of properties to identify matter through standard 5-PS1-3: Make observations and measurements to identify materials based on their properties. The investigations and experiments during this unit will focus on physical and chemical changes that occur when mixing matter which is addressed in standard 5-PS1-4: Conduct an investigation to determine whether the mixing of two or more substances results in a new substance.
This specific lesson covers standard 5-PS1-4 because students are changing various types of matter and determining if the change that occurred results in a new substance, or simply changes the form of the existing substance.
Students will observe matter change form and determine if it is a physical change or chemical change based on indicators they observe.
Students will demonstrate success on meeting this goal by correctly identifying the changes on their investigation sheet.
Preparing for Lesson:
The following materials are needed for each group to complete the chemical change demonstration:
- small ziplock bag
- tbs of Calcium Chloride
- Copy of the Physical Change vs Chemical Change Foldable for each student, prefolded
- Copy of the Physical and Chemical Change Investigation Sheet for each student
- Physical and Chemical Change Station Rotation sheets printed so that you have the directions
- Each station has materials that you will also need to prepare
- Station 1 - colored paper cut into squares for origami and origami instruction template that you can print off from the link in the Explore section.
- Station 2 - empty water bottles prefilled 3/4 full of vegetable oil, water, Alka Seltzer tablets, food coloring
- Station 3 - Aluminum foil cut into 10" x 10" squares, 50 - 80 pennies, tub for water
- Station 4 - Large Bowl, empty water bottle, vinegar, baking soda, balloon, funnel, spoon
- Station 5 - small cups, water, microwave, Borax, bottle of glue, craft sticks, ziplock bag
- Station 6 - apple for each group, plastic knife, plate
No preparation needed, this is a wrap up discussion for sharing our findings.
Introducing Chemical Changes:
Students have not yet been introduced to physical or chemical changes. Up to this point in the unit, they have been focusing on properties of matter. In order to introduce them to chemical changes, I have chosen an activity that leads them into thinking scientifically about how heat is created from a mixture. I want them to make observations that lead to their own discovery of a chemical change.
I provide each group with a ziplock bag with a little water in it. I tel them that we will be adding a chemical called Calcium Chloride to the bag. Calcium Chloride is a substance that is found in most science labs in schools, and can be purchased online pretty cheap through companies like Amazon. I tell students that once the Calcium Chloride is added to their bag, they need to seal their bag completely closed and then mix the ingredients together by swooshing the bag in their hand. I tell them that will observe something happening and I don't want them saying it out loud and ruining it for the other groups, just observe and see what occurs and then we will discuss.
I choose one student to add about 1 tablespoon of Calcium Chloride to each bag. As she adds the substance to each bag, students begin noticing the change that is occurring immediately...the water is getting hot. You can see some of reactions of students in the video of students observing chemical change.
After observing the change I ask students what happened and why it happened. They can easily tell me that the water got hot, but explaining why is not as easy. One student said it was the H2O, trying to pull in the compound term for water since we had been talking about compounds. Another student said it was the chlorine (calcium chloride), but when asked if the calcium chloride was hot she said no and could not elaborate on that. The next student I called on built off what she had said, that when the chemical mixed with the water it produced the heat. I told them that is exactly right, that by mixing the Calcium Chloride with the water, a chemical reaction occurred releasing stored energy in the form of heat. Something new had been created that was not there before, heat. This realization led into our lesson for the day, differentiating between physical and chemical changes.
Physical and Chemical Changes Foldable:
I provide each student with a Physical Change vs Chemical Change Foldable that is already folded trifold for them, and ask them to glue it into their science notebook. Foldables that can be glued into their science notebooks are a great tool because it provides them with a resource that is interactive to help them review and study throughout the year. After it is glued in, I ask students to look at the pictures on the front of the foldable. One side has cakes and pies that were just baked, fireworks, and a fire burning. The other side has ice melting, salt being added to a cup of water to dissolve, and a stick breaking in half. I ask them which side they believe illustrates physical changes and which side would illustrate chemical changes. They correctly identify the side with the fire as the chemical changes and the side with the ice melting the physical changes. I labeled my foldable, which is displayed on the overhead for students to see, and students copied onto theirs. Having my foldable up for the class to see, helps the ESE and ELL students with spelling, and keeps those who struggle with following directions focused on what they should be doing.
After labeling the front, we open the foldable and create a T-chart on the inside to compare physical and chemical changes. I use T-charts often as a way to help organize similarities and differences between two things. As I write down information in my foldable, students copy into theirs. We begin with the headings which align with the front. Under that I record on the physical changes side "Does not create something new", and on the chemical changes side, "Creates something new". I go on to describe how the arrangement of particles changes in a physical change, but the particles themselves do not change. However, in a chemical change, the bonds between particles are broken (bonds is a word they are familiar with from previous lessons), and molecules are changed. We record this information in the foldable as well. The final thing that we list in the foldable are identifiers for each type of change. I inform students that these indicators are what they will be watching for today as they create some physical and chemical changes. We create the following list in our foldable:
Physical Change Chemical Change
- Change in size - Change in color
- Change in shape - Change in smell
- Change in state - New matter is created
freezing (bubbles or fizzing indicate
melting a gas is being produced)
evaporating - Heat or light created
The Focus of the Investigation:
After our foldable is created, it is time to investigate some changes to practice identifying them as physical changes or chemical changes. The students get very excited about some of these activities so it is important to help guide them to help them focus on what is most important, observing the changes that are occurring and watching for one of the indicators listed in the foldable. The Physical and Chemical Change Investigation Sheet that I use for this lesson has students identify properties before and after to help them notice these changes.
Investigating in Small Groups:
We do the rotations as a class, but each group completes the activities and investigation sheet together. Each activity should only take about 5 minutes. We start with station 6: Apple Colors. I have groups record their observations on the properties of the apple before they change it. Then they cut their apple into slices and leave it out on a plate while we complete the rest of the activities. This allows the apple to have time to begin to turn brown.
Next, we move to the station 1 activity: Origami. I chose three items that students could choose from but due to time, I had them all make the dog because it was the easiest. There are many free templates to choose from online. Students recorded properties of the paper before changing it, then followed the directions for folding it to create a dog, and recorded how the properties have changed. They then indicated if they thought it was a physical or chemical change and what indicator supports their reasoning.
We move on to station 2: Lava Lamps. I provide each group with 2 empty water bottles with lids. I have already prefilled them 3/4 full of vegetable oil to save time. I send one group to the sink at a time to fill them the rest of the way with water. As they are filling them with water, I provide each group with a thing of food coloring and one Alka Seltzer tablet. When all groups are finished adding their water, I point out that the water sank to the bottom because it is more dense then oil. Density is a term that will come up later when separating mixtures so I wanted to point it out now. I tell groups to add about 8 - 10 drops of food coloring to their bottle. They notice that the food coloring does not mix in right away, it gets caught up in the oil and stays in little drops. I instruct them to break their Alka Seltzer tablet into small pieces (quarters), drop one piece in at a time and wait until the fizzing stops. Students notice that this causes the food coloring to mix in as the bubbles rise to the surface. You can see in the video of lava lamps being made that students observe the bubbling that occurs which is the indicator of a chemical change.
Station 3 is building a boat out of an 10" x 10" square of aluminum foil. Each student gets their own foil, just as they did with the origami, and they each create their own boat. I tell them that we will measure how much weight (pennies) they each hold the following day. Because I only have 1 hour with each class for science, this is something we don't have time for during the investigation. If you have time you could always do it after the stations, or later in the day. After students record the beginning properties, they are allowed to start making their boats. There are so many different styles created, some are long like hotdog buns, some are flat like squares with small walls up around the edges, and the most creative thing I saw was students taking their foil and wrapping it around the bottom of their lava lamp bottle to create a mold. Not all boats were successful in holding many pennies as you can see in the video of boat that was not successful. Others held over 30 which you can see in the video of boat that was successful.
After boats are built, we move on to station 4: Balloon Blow Up. I choose two students to demonstrate this activity for us instead of each group doing it. I show all groups the vinegar and baking soda which are the two ingredients being used for this activity. They record properties for each item. Then the two students I choose to come up, follow the directions outlined on the station sheet, and everyone observes the change that occurs. You can see in the video of balloon blow up activity that it takes the student quite a while to get the balloon attached to the bottle. By the time he was done getting it on, he must have poked a small hole in the balloon because the air was leaking out on the side. The balloon will usually blow up much larger than in this video.
Our final station is station 5: Glue Bouncy Balls. I show each group the ingredients for this station, Borax, water, and glue, and have them record beginning properties for the items. I provide each group with 2 small cups of warm water and add 1 tbs of Borax to each cup. Students use a craft stick to stir it to get it to dissolve. I then place 1 bottle of glue at each group, and tell students to pour half of the bottle in each cup of Borax solution. After adding the glue, they use the craft sticks to mix it together. They note the change that has occurred and lists the new properties. The Borax causes the glue to become hard and rubbery. Students are able to take it out of the water solution and roll it into a ball which will bounce like a bouncy ball. You can see in the video of glue bouncy balls being made that the students really enjoy this one. You have to make sure students break all of the glue pockets in the ball before taking out to roll it in their hands or glue will pop out of the pockets and make a mess. You can see the second group in the video is trying to break all of their pockets by poking them with the sticks.
After making the glue bouncy balls, students record the end properties for their new substance, and for their apple that was cut at the beginning of the investigation. The apple slices have now started turning a brownish color which is not how they appeared before. As they finish up their lab sheet, I call groups over to throw out their water, wash hands, and get zip lock bags for their glue balls. Each group has 2 lava lamps, and 2 glue balls that they get to keep. Each group has four students so each student will keep one of the items.
Sharing our Findings:
After all activities are completed, we come back together as a whole group and share our findings. We discuss the changes that occurred in each activity, if it was a physical or chemical change, and what evidence we have to support that. This is important so that I can check for understanding by seeing if they got the correct answers. It also allows them to practice with the science vocabulary and to argue their opinions if any groups have different thoughts. Some of the answers I got during the discussion are noted below:
Station 1: Origami
The paper changed size and shape but it is still paper so this was a physical change. All groups agreed with this.
Station 2: Lava Lamp
When the Alka Seltzer was added, it caused the food coloring to mix with the water, and bubbles were formed. The water stayed in a blob together after the Alka Seltzer was added. The bubbles indicated a chemical change occurred. All groups agreed with this.
Station 3: Build a Boat
The aluminum foil changed size and shape but it is still aluminum foil so it was a physical change. All groups agreed with this.
Station 4: Balloon Blow Up
The vinegar and baking soda bubbled when mixed together so it was a chemical change. I asked why the balloon blew up and students were able to tell me a gas was produced. I asked them if that gas was present before and they told me no. I said that means a new substance was created which could have been another thing written down on lab sheets.
Station 5: Glue Bouncy Ball
The Borax and water caused the glue to change into a solid so instead of having glue, we ended up with a rubbery ball which was something new. I wanted to make sure I made reference of a change of state here so that I know students are clear on the the difference that occurred. I asked them why things usually change state (this is review from previous lessons in this unit) and they tell me heat is added or taken away. I asked them if we froze the glue in this activity causing it to change state and they tell me no. I ask them what caused the glue to change state. They tell me the reaction with the Borax and water. It is important to note this because on the foldable it states that a change of state is a physical change, but students need to understand that is referring to a normal change of state like ice melting, not a change due to a reaction.
Stations 6: Apply Colors
One student tells me that it is a chemical change because the apple changed color because it is starting to rot. This is the change that I was envisioning when I created the lab sheet. However, I had another group that told me it was a physical change because they cut the apple so it was in several smaller pieces but it was still an apple. I told students to write down both, because both are correct. The cutting of the apple was a physical change, the color change due to the reaction with the oxygen is a chemical change.