Using Properties to Separate Mixtures
Lesson 9 of 10
Objective: SWBAT identify properties of given items and select a property that would help them easily separate the items from each other.
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 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 is linked to standard 5-PS1-3. We will be identifying physical properties of various types of matter and using those properties to separate them.
The goal of this lesson is for students to apply their knowledge on properties of matter, to help them come up with a way to separate mixtures easily.
Students will demonstrate success in meeting this goal in two different ways. One way is by correctly identifying the property that is different and that will be able to help them separate the mixture quickly and easily. The other way to demonstrate success is by correctly describing how they would separate 3 items on the exit ticket provided.
Preparing for Lesson:
Have common examples of mixtures that student experience in real like. I chose to provide each group with a cup of cheerios and milk and a bag of Cheez-It Party Mix.
Have the following tools ready to show students during the discussion:
- filter paper
- cup of water
- copy of the Using Properties to Separate Mixtures Lab Sheet for each student
- Tray of items for each group, the tray should have the following items on it:
- 1 magnet
- 1 sieve
- 1 spoon
- 2 paper plates
- 1 funnel and a couple of pieces of filter paper
- Several premixed mixtures for each group (you will want them to be the same for each group). The mixtures I used are below:
- sand and pebbles
- sand and iron filings
- cheerios and milk
- salt and pepper
- marbles and small plastic squares
- copy of the exit ticket for each student
Connecting the Lesson to the Real World:
I begin today's lesson by providing each student with a cup of cheerios. I add a little milk to each cup so that the cheerios are floating in the milk. I also give them a little Ziplock bag of Cheez-It Party Mix. I tell students that they use properties and tools to help them separate mixtures everyday, they just don't think about it in that scientific way. I ask them how they separate their cereal from their milk in the mornings. They tell me with a spoon. I ask them what property of the cereal is different from the milk that keeps it floating on top of the milk so it is easy to separate using a spoon. They tell me that the cereal is lighter than the milk. We briefly discussed density in a previous lesson when we mixed oil and water so I remind them of this term. Density is not a property that will be assessed so it is not necessary to stress this term.
I then refer students to the bag of Cheez-It Party Mix and tell them that my favorite parts are the Cheez-Its, the pretzels, and the croutons, but I really don't like the little ball things in it. I ask them how I could get those pieces out. They tell me just to pick them out. I ask what property I would be using to help me separate them. They tell me the shape and another student says I could use color as well because they are white.
I provide each student with a spoon and let them eat these treats as their snack for the day. While they are eating their snack, I continue on with the lesson introducing some new tools that they will use for separating mixtures.
Before beginning the lesson for today, I introduce some new tools to students. These tools are what the students will be choosing between when deciding what to use to separate mixtures. I briefly discuss the tool, how it works, and what property it would work to help separate.
The first tool is a magnet. Students have seen a magnet and know how it works so this is a pretty easy introduction. I show them the magnet. I ask them what it is and how it works. They identify it as a magnet and tell me it attracts metal. I ask them if all metal is attracted to a magnet? They tell me no and I ask for an example of a metal that is not magnetic. They cannot answer this so I ask if anyone has stainless steal appliances at home. Several students raise their hands. I ask them if magnets stick to their refrigerator and they tell me no. I say, steal is one metal that is not magnetic. I tell them that magnetism is one property that can help separate magnetic metals from other materials. I refer to the popular kids movie Toy Story 3. I ask how many students have seen that movie and most raise their hand. I play a video clip from the movie as an example of how a magnet separates mixtures.
The next tool that I introduce is a sieve which I tell them can be called a sieve, screen, or sifter. I show this tool to the class and ask if anyone knows how it works. A student tells me that one item goes through it, and the other item won't. I ask what types of items would go through it, and they tell me small items. I point out that size is a property that can also be used to separate mixtures. If one item is small, and the other is large, a sieve can be used to separate them. I tell them that they may see something similar to this used at home when their parents make pasta. They usually use something like this to separate the pasta from the water after it is cooked and many students comment that their parents do use it or that they have even used it before.
The last tool I introduce is a funnel and filter paper. I show the filter paper and after telling the students what it is, they tell me that it is used for making coffee. I tell them that the water heat up the coffee and drips through the filter paper leaving the ground up coffee on top of the filter paper so that it isn't in the coffee you drink. So even in a coffee maker, the filter paper is being used to separate a mixture. I ask them what property this would be used for. They aren't really sure about this so I have to elaborate more by asking what type of matter will go through the filter paper and they tell me liquids. I ask if solids will go through as well and they say no. This is the property that filter paper will be used for. I show them how I place the filter paper in the funnel to help guide the liquid into the cup or bowl it is going into so that it doesn't make a mess.
I also show students a cup of water and explain that water is also a tool that can be used to separate mixtures. I ask what would happen to salt if we added it to water and they tell me it would dissolve. I ask if sand would react in the same way and they tell me no, sand does not dissolve, it would just sink to the bottom. I explain that solubility (ability to dissolve) is another property that can be used to separate mixtures.
Teacher Led Small Group Investigation:
I am doing this as a teacher led investigation instead of just handing the kids the materials and letting them investigate in their groups to help keep them focused. For some activities, such as experiments, the kids have a very organized set of procedures to follow and data to collect. In activities such as this investigation, it is less organized and they tend to want to go straight to playing with the tools instead of taking the time to identify the properties and relating the separating of mixtures to that. Completing it as a teacher led investigation, I have the ability to control the pace of the lesson and make sure students are focusing on the properties first, then using those properties to separate the mixtures.
I provide each group with a tray of mixtures already combined, several empty cups, a magnet, a sieve, a spoon, and a funnel with filter paper. I also provide each group with 2 plates for separating the items on. The items that I have combined to create mixtures are sand and pebbles, sand and iron filings, marbles and small plastic squares, salt and pepper, and cheerios and milk. The salt and pepper and cheerios and milk are not in the photo below because I put those out right before they test just so the cheerios don't get soggy and the smell of pepper does not fill the room.
I provide each student with a copy of the Using Properties to Separate Mixtures Lab Sheet that is precut at the margins so it will fit into their science notebooks. I have them clear off their desks so that they will have plenty of work space as this can sometimes get a little messy.
Pebbles and Sand: Using the Property of Size to Separate:
The first item that students will separate is the sand and pebbles. I ask groups to observe that mixture, then discuss and record properties of each item on their lab sheet. I circulate to listen to group discussions and make sure students are not playing with the tools. After all groups have recorded the properties, we discuss a few of them. Students tell me things such as the pebbles are green and the sand is tan, both are solids, neither will dissolve in water, and one has small grains and the other is larger. I point out that neither will dissolve in water so we can rule out using water to separate them. I ask what other property is different that we might be able to use to separate them. All groups agree that the size difference will help us separate this mixture. I instruct them to pick up the tool that is used for separating things of different sizes and hold it up in the air. All groups select the sieve. I allow groups to separate the mixture into two piles. You can see a group completing the activity in the video of students separating pebbles and sand.
Iron Filings and Sand: Using the Property of Magnetism to Separate:
The next mixture I have students observe is the iron filings and sand. I circulate to listen to conversations as groups discuss the properties of each item. After all groups have a few ideas listed on their lab sheet, I ask them to share. Groups tell me properties such as the sand is tan and the iron is black, both are solids, both have small grain sizes, neither will dissolve, and iron is magnetic. I point out that I heard a group say both are small, which eliminates the sieve as our tool. I also heard a group mention that neither will dissolve so we cannot use water. I ask which property is different between the two items that we could use to help us separate the items. Students tell me that iron is magnetic and sand is not so we can use a magnet.
I allow groups time to use the magnet to separate the iron from the sand. Students always find this one of the coolest activities and tend to get excited when they begin to see the iron come out of the mixture. They do have to touch the iron to get it off the magnet so it is important to remind them to keep all of the iron on the plate, and after they touch it to keep their hands away from their mouth and eyes. I pass out hand wipes to students to use after they have touched the iron. You can see in the video 1 of students separating iron filings and sand that everyone in the group wants to touch the iron and eagerly reach to help pull it off the magnet. In the video 2 of students separating iron filings and sand the girls are not real sure about touching it and go about removing it very slowly. You will have a variety of reactions but all the students will enjoy this activity.
Separating Cheerios and Milk:
The third mixture that we separate is Cheerios and Milk. Although we did this in the warm up, I want to do it again using the new tools that were introduced. Groups identify properties of both items in the mixture and complete the lab sheet. I circulate to listen to group discussions and then have groups share. They tell me properties such as the cheerios are tan and the milk is white, and that the cheerios are a solid and the milk is a liquid. I ask them if we have one item that is a solid and the other is a liquid, which tool could we use to separate them? I am expecting students to tell me the filter paper and funnel. I ask groups to hold up the item they would use and see that half of the group select the filter paper and funnel, and the other half hold up the sieve. I did not even think about the sieve but both are correct. I tell them that we will see which was the better option in tools to use and let groups separate with the tool they chose.
The sieve actually worked much better than the filter paper and funnel. You can see in the picture above that the milk takes a long time to drain out because it is so thick and because the cheerios clog up the space in the funnel. Many groups that used the sieve, used it similar to a spoon and just scooped out the cheerios which worked quickly.
Separating Salt and Pepper:
The last item that we have time to investigate is salt and pepper. As groups discuss properties and record them on their lab sheet, I circulate to listen to conversations. I have groups share after everyone has a few properties listed. Groups name properties such as salt is white and pepper is black, both have small grains, both are solids, the salt will dissolve in water and the pepper will not. I ask them what property is different that we could use to separate them. A student tells me solubility, the salt will dissolve and the pepper will not. I provide each group with a cup of water and have them pour some of the mixture into the water and stir with the spoon until the salt dissolves. I point out to students that the mixture is not separated yet and ask how we could get the pepper out of the mixture now. Students tell me to pour it through the filter paper and the pepper would stay on top. I allow some time for groups to do this.
You can see a Photo of completed lab sheet here.
Applying What They Learned to a Mixture of 3 Items:
As students clean up their work area and return materials on the trays to the front table, I pass out the exit ticket. The exit ticket question requires students to take the process one step further by explaining how they would use properties to separate three items, salt, sand, and iron filings.
After students have completed the exit tickets, I collect them and separate them into 3 piles: met goal, almost got it, and needs reteaching. In order to get in the met goal pile, the student would have to mention that they would first use a magnet to separate the iron filings from the mixture. Then they would use water to dissolve the salt. The final step would be to pour the mixture of salt, sand, and water through filter paper to get the sand separated from the salt.
I would also like to see if any students take it one step further by putting the additional step of evaporating the water so that the salt would be left. It does mention in the exit ticket question that students are supposed to get the three items into three separate piles. In order to get them into 3 piles, you would have to evaporate the water. I know having this final step is not likely since it is not something we discussed today, but we have separated salt from water through evaporation in prior lessons so they do have that background knowledge to refer back to.
Students who got at least one of the steps correct, but not all of them would be put in the almost got it pile. Students who were unable to identify any of the correct steps or tools, were placed in the needs reteaching pile.
Results from Exit Ticket:
I was pleased to see that I did not have any students in the needs reteaching pile. All students correctly identified using a magnet to remove the iron filings. I only had about 8 students out of 40 that proved mastery on the exit ticket and the rest were in the almost got it pile. The error that about 70% of the students made was that most students said to use the magnet to get the iron filings out, then add water to separate the salt from the sand. They stopped there. When I reviewed this with them, I pointed out that by adding water the salt is dissolving but what would I now have in the cup? Salt, water, and sand. By stopping after adding the water, the students did not separate the sand from the salt. I had a couple of the students who got it correct by explaining the final step, which was to use filter paper to separate out the sand. I did not have any students take it to the next level and mention evaporation would need to be used to get the salt by itself which I kind of expected. I did mention this when reviewing.