The Why Behind Teaching This:
Unit 2 addresses standards related to matter and its 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 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 addresses standard 5-PS1-3: Make observations and measurements to identify materials based on their properties. In this lesson, students gather information about both physical and chemical properties of five white powders. They then use these properties to identify the powders again when unlabeled.
The goal of this lesson is for students to demonstrate an understanding of how to use physical and chemical properties to correctly identify matter.
Students will demonstrate mastery by correctly identifying the substances on their lab sheets and then sharing their findings with the class.
Preparing for Lesson:
(insert photo of construction paper set up)
(Insert photo of construction paper set up)
I begin today's lesson by providing each group with 5 Ziplock baggies labeled A, B, C, D and E. Each baggie contains about the same amount of one of the following: salt, baking soda, corn starch, or sugar. I ask groups to discuss some of the properties for the substances and create a list on their whiteboards. I circulate and listen to conversations while groups discuss the properties and create a list.
After a few minutes, I ask groups to share their list of properties. Groups have things such as white, powdery, and solid. I ask students if these are all examples of physical properties or chemical properties, students tell me physical which is correct.
I tell them when physical properties are the same for a substance, scientists need to rely on chemical properties to help them identify the substance. I remind students that chemical properties are how a substance reacts to another substance. I ask them to think about some of the activities we have done, and see if they can come up with a list of chemical properties. As students discuss this and create a list on their whiteboard, I circulate to help lead conversations and listen to the science talk taking place. The students are writing things such as dissolving, changes color, fizzes or bubbles. As they share these items on their whiteboards, I ask guiding questions about what tests were have completed that were evidence of these. They are able to tell me that Borax reacted with glue, and baking soda reacted with vinegar when we did chemical changes. I ask them what happens to the Borax when it mixes with the glue and they tell me the glue clumps together. I ask them what happens to baking soda when it mixes with baking soda and they tell me it bubbles.
I inform students that these are a couple of the reactions they will be watching for today. They will become the scientists that will be testing the properties of various white powders and using those properties to identify them.
Preparing for the Investigation:
Because we are using chemicals for this investigation, there are a few additional safety rules that I need to go over with the class. I place the Lab Rules for White Powder Lab on the overhead and go over each one with the class. I make sure everyone is clear on these rules before I pass out safety goggles to each student and remind them that they need to remain on throughout the entire investigation. I stress to students that when handling chemicals they should be extra careful, and if anything spills they need to raise their hand and let me know so that I can clean it up.
Investigating Physical Properties:
I begin by calling up the materials manager from each group and asking them to bring their baggies of white powders and white board and markers up with them. I take those materials, and I provide them with a tray of materials. I ask groups not to touch any of the materials until I have given them directions. Each group gets one tray with the following materials: a small cup of salt, baking soda, corn starch, Borax, and sugar, each labeled so that groups know exactly which substance is in each cup, a piece of black construction paper that has been sectioned with 3 rows and 5 columns, each labeled with one of the five white powders, 4 hand lenses, and 5 spoons. After each group has their materials, I pass out an investigation sheet to each group and I place one on the overhead so that I can refer to it throughout the guided practice section of the lesson.
The first thing I ask students to do is to observe the white powders and complete the first column of their investigation chart labeled "color". This should only take a few seconds because all should be labeled as white.
I then ask students to feel the texture of each substance by pinching a small amount between two fingers, keeping it all in the cup. I point out the second column that says "grain size" and tell students to pay close attention to how the grains feel because that is what they will need to record after feeling each substance. I circulate to ensure that students are observing accurately and are not making a mess or removing any of the substances from the cups.
Investigating Chemical Reactions:
After groups have the texture recorded, I tell them to remove all materials from the tray and place the black construction paper flat on the tray. I point out the first row of circles on one group's paper and tell groups that they will need to place one teaspoon of each powder in the circle labeled as that substance. I model this by placing one teaspoon of corn starch on the first circle for group one. I point out that my teaspoon is flat, not a huge heap of the white powder. I give groups a minute to get each substance out on the correct circle.
After groups have their substances out on the construction paper, I tell them that their first reaction test will be with the water. They should take turns adding a couple of drops of water to each substance, one at a time, and observing what happens. The hand lenses are if they need to look at the reactions more closely. Things to watch for, are dissolving, clumping together, changing in appearance, or bubbling. I pass out a cup of water, labeled as water, with a dropper in it to each group and allow them to test each substance. I circulate while they test, observe, and record their observations in the investigation log.
I then ask them to get out another flat teaspoon of each powder and place it in the correct circle in the second row. I wait for a minute while groups do this. I then tell them the second reaction they will be testing is the vinegar. I pass out a small cup of vinegar labeled as vinegar and a new dropper to each group. I tell them that they should add a couple of drops of vinegar to each substance, observe the reaction, and record their observations. I circulate while groups complete this part of the investigation.
The final reaction that groups will be testing is the reaction to Iodine. I ask students to get out a teaspoon of each powder and place it in the last circle labeled as each substance. Once groups have the substances out, I pass out a small cup of Iodine labeled as Iodine with a new dropper. I remind them to add a couple of drops to each substance, observe the reaction, and record their observations.
Video of group observing the texture of white powders shows a group observing the grain size of the powders by using their hands lenses and by pinching a small amount in their fingers. The Video of students testing water reaction with white powders shows students adding a few drops of water to each pile of powders and discussing their observations. The Video of students testing vinegar reaction with white powders shows a group adding drops of vinegar to each white powder and discussing their observations of what is happening. The Video of students testing iodine reaction with white powders shows a group adding drops of iodine to each white powder. You can hear this group discuss how the drops roll off the powder being tested which was surprising to them.
Identifying the Mystery Powders:
I walk around to each group with a trash and throw away their piece of black construction paper that has the substances tested on them. I circulate to collect the cups of white powders leaving all other materials at their desks. I pass out five baggies of white powders labeled A, B, C, D, and E and a new piece of black construction paper with circles labeled with those letters. The powders in the baggies are the same powders they just tested, but students do not know which powder is which.
I inform students that they will be completing this portion of the investigation with their groups, at their own pace. I point out the bottom chart on the lab sheet and tell them that their task is to use the properties that we just tested, to help them identify each of the unknown powders. They should begin with the grain size, and then check reaction to each of the liquids. I ask if there are any questions for getting started, and remind them that I will be circulating and expect to see them doing the right thing or they will be removed from the group.
As groups begin testing, I circulate to observe, listen to the science talk that is occurring, and ask questions. I remind students that they should be filling in their predictions on what each substance is as they are making their observations.
You can see students completing their independent tests in the video of students testing mystery powders with water and the video of students testing mystery powders with iodine. You don't really hear students making their predictions in these videos because most groups made these predictions while feeling the powders before they begin testing with the liquids. Some predictions changed as they tested, some remained the same.
Were Your Identifications Correct?
As groups finish testing each substance and making their identifications, I take the trash over to throw away their construction paper with their substances tested on it, and ask the materials manager to gather all materials on the tray and take everything over to the table. I ask them to pick up a white board and marker when they drop off their materials. I ask groups to record their identifications on the whiteboard while they wait for other groups to finish.
Once all groups have their materials returned, and I see their identifications for substance A, B, C, D, and E, on their whiteboards, I ask groups to hold up their findings. Everyone should have A listed as Corn Starch, B listed as Borax, C listed as Salt, D listed as Baking Soda, and E listed as Sugar.
As well as sharing their findings with others, which is an important step in science, I am also using this as a way to assess understanding. If there were groups that were way off on their identifications, they clearly did not make accurate observations, or complete the investigation accurately. Once reason we did the first set of testing together was so that I could check that all groups were completing the task correctly and gathering accurate information. If they were not able to correctly identify the substances when testing on their own, that means they did something wrong during their independent group investigation that I will need to address. In the first class, 3 out of 4 groups correctly identified all of the white powders, the last group had salt and sugar mixed up. In the second class, all groups were able to correctly identify all white powders.
Reflecting on The Investigation:
I ask students to think about why I had them test the mystery powders. If we already tested the properties and knew how the substances would react, why didn't we just stop there? I would like to see that students are able to make the connection that they were applying what they learned to an actual test, similar to what scientists might do in the real world. If we have stopped after testing each powder originally, they would not have had the opportunity to use the properties for identification purposes. Students were able to explain this to me.