Mystery Package
Written by: UTeach Outreach Date of lesson: Fall 2014 Grade: 5th Grade Heterogeneous Classroom Length of Lesson: 50 -­‐ 55 minutes Source of Lesson: UTeach Outreach TEKS Addressed: 5.(2) Scientific investigation and reasoning. The student uses scientific methods during laboratory and outdoor investigations. The student is expected to: (C) collect information by detailed observations (F) communicate valid conclusions in both written and verbal forms; 5. (5) Matter and energy. The student knows that matter has measurable physical properties and those properties determine how matter is classified, changed, and used. The student is expected to: (A) classify matter based on physical properties, (C) demonstrate that some mixtures maintain physical properties of their ingredients such as iron filings and sand; (D) identify changes that can occur in the physical properties of the ingredients of solutions such as dissolving salt in water. I. Overview Students will investigate the ingredients of a “mystery package” (similar to sand art) that was said to be delivered to UT without a materials list. During this investigation they will explore the physical properties of each layer of the mixture, including color, texture, and changes in water. Following the students’ investigation they will need to report back to UT on what they discover, including categorizing the ingredients as homogeneous or heterogeneous. II. Performance Objectives 1. Students will identify the ingredients of a mixture by exploring the mixture’s physical properties and identifying changes that can occur when water is added. 2. Students will demonstrate that some ingredients of a mixture maintain their physical properties throughout the investigation. 3. Students will apply their knowledge by solving a variety of problems involving mixtures. III. Resources/Materials: All materials used in teams of four students Copyright UTeach Austin 2013
Engage (per class): • Large envelope with a mailing label on it. • Envelope with a stapler in it. • Envelope with pens and pencils in it. • Envelope with marbles in it. Explore (Per Group of 4 students): • One vial containing a layered mixture of pepper, magic sand, salt, regular sand, instant snow with a cotton ball between each layer. Make sure there is an ample amount of each and the cotton is tightly packed.) • An 8-­‐10oz cup of water • Ice Cube Tray or 1 oz cups labeled 1-­‐6 • Water • Pipette • Magnet • Small sampling spoons • Tray or paper plate • Hand lens • 6 toothpicks • Paper towels • Jumbo paperclip straightened with a hook at the end to get out the cotton layers • Newspaper Explanation: per class • Physical properties list • 1 Bottle with lid, half-­‐filled with water, half-­‐filled with sugar • Bottle with lid, half-­‐filled with water, half-­‐filled with oil Elaboration: per class • Pint size container of salt water • Pint size container of salt crystals left from evaporation • Mixture of sand and iron fillings in a petri dish Copyright UTeach Austin 2013
IV. Advanced Preparation The beakers of water will need to be filled with water for each group. The oil/water bottle and water/sugar bottle will need to be prepared. Ensure vials are prepared before class begins. V. Supplementary worksheets, materials, handouts “Mystery Package” Observation Worksheet Show Off What You Know -­‐ “Mystery Package” Job cards VI. Background Information: College Level A property of matter is any characteristic of an object or material that can be used to describe, sort, or identify it. For example, a piece of copy paper is white. A carrot is orange. Paper is flat, and carrots are conical. The color and shape of a carrot or piece of paper are properties of those materials, because they can be used to identify them or distinguish them from other objects. Any time you sort or describe different objects, you are making distinctions based on the differing properties of the objects. Properties of matter are broken down into physical properties and chemical properties. Copyright UTeach Austin 2013
Physical properties are properties that can be measured or observed without changing what the object is made of. For example, a piece of computer paper is white, flat, bendable, has a certain height and width and thickness, and has a certain mass. Any of these properties can be determined without changing the paper. A piece of computer paper is also foldable and can be torn in half. These, too, are physical properties, because even though they leave the paper in a different state than it was before, the identity of the material itself has not changed -­‐-­‐ the paper might be in more pieces now than it was before, but it is still paper. Many physical properties are easily observable or measurable properties, such as shape, color, height, volume, mass, density, temperature, and odor. These can be determined without doing anything that changes the object. Other physical properties might not be evident without doing something to the object. Properties such as melting point, boiling point, malleability, and solubility require doing something to the sample that changes it in some way. These are still physical properties because the chemical formula of the material does not change when these properties are examined. When solid ice melts to liquid water and then evaporates to gaseous water vapor, the chemical formula of the particles (H2O) does not change. The same particles that were there before the change are still there after the change. Any change in a material that does not involve changing the chemical formula of the substance is a physical change. Burning a piece of paper does turn it into something else (mostly carbon dioxide and water). Since the chemical formula of the material changes, this is a chemical change. Rusting a piece of iron is a chemical change because the ending material (rust, Fe2O3) has a different chemical formula than the starting materials (iron, Fe, and oxygen, O2). The particles that were there before the change are now gone and have been replaced with different particles that have different physical and chemical properties. All chemical changes involve a chemical reaction that changes the chemical formula of the material in question. Chemical properties describe a material's ability to react in a particular chemical reaction. Flammability is a chemical property of paper. Rusting is a chemical property of iron. The fact that a material does not participate in a chemical reaction is also a chemical property. Therefore, another chemical property of iron is that it is not flammable. A chemical property always refers to some type of chemical reaction, and always indicates whether or not that reaction will change the identity (the chemical formula) of the material. Physical changes are sometimes mistaken for chemical changes. When sugar is dissolved in water, a sparkly white crystalline solid "disappears" into a colorless aqueous solution. This is a physical change, not a chemical change, because the chemical formula of the sugar molecules has not changed. The molecules that were present as a white crystalline solid are the same molecules that are now dissolved in the water. Another physical property of the sugar -­‐-­‐ its sweet taste -­‐-­‐ has not changed despite the change from solid to aqueous form. Dissolving salt in water is similarly a physical, not chemical, change. Solid table salt (NaCl) is a collection of sodium ions and chloride ions bound together in a rigid arrangement. When salt is dissolved in water, the sodium ions and chloride ions spread out and move freely, but they are still the same sodium ions and chloride ions that were in the original solid. Copyright UTeach Austin 2013
Evaporating away the water (another physical change) brings the ions back together again and recovers the salt in its original form. This shows that even though some of its physical properties, such as its color, changed when it was dissolved, the chemical formula of the salt never changed. Adding salt or sugar to water is an example of a mixture. A mixture is formed when two or more substances are combined but do not react with one another or bond together. The chemical formula of each component of the mixture remains unchanged and the individual components can be recovered from the mixture through a physical separation. Sometimes the components of a mixture are easily identifiable, such as the ingredients that make up a salad, and sometimes the components mix so thoroughly that the individual components can no longer be recognized, as in milk or saltwater. A mixture that has a uniform composition and appears to be a single substance is called a homogeneous mixture, or solution. Kool-­‐Aid, milk, and gasoline are all examples of solutions. A solution is made up of a solvent and one or more solutes. The solvent is the substance doing the dissolving (for example, the water) and the solute is the substance being dissolved (the sugar or salt). In the case of two gases mixing, the solvent is considered to be whichever gas there is more of, so our atmosphere is a gas phase solution made up of oxygen, argon and various trace gases dissolved in nitrogen. Metal alloys are solid solutions of one metal dissolved in another. Again the solvent is whichever metal there is more of, so brass is a solution of zinc dissolved in copper. A heterogeneous mixture results when the components making up a mixture are not evenly distributed and are easily identifiable. When sand is added to water it sinks to the bottom and the components of the mixture are readily apparent, so sand in water is an example of a heterogeneous mixture. Other heterogeneous mixtures include Raisin Bran and oil and vinegar salad dressings. Some heterogeneous mixtures will appear homogeneous when sufficiently stirred, but if the components settle out when allowed to sit undisturbed, the mixture is heterogeneous. Any time there are two different phases in a mixture, such as solid and liquid (sand in water) or two different layers of liquid (oil and water), the mixture is heterogeneous. Because mixing does not involve a chemical reaction and is a purely physical process, the components of the mixture can be recovered through a physical separation. The physical separation of two substances is always based on differences in the physical properties of those two substances. For example, water boils at 100°C but salt is a solid at that temperature, so a mixture of salt and water can be separated by boiling away the water. A mixture of golf balls and ping pong balls can be separated by dumping them in water, where the golf balls will sink while the ping pong balls will float. Once a mixture has been separated into its individual components, the physical properties of each component can be used to help identify it. In this activity, seven different unknown materials will be identified by comparing their physical properties (color, magnetism, solubility, sink or float, etc.) to the physical properties of a list of known materials. Some materials used in this lesson are magic snow and magic sand. Magic snow or instant snow is also extremely absorbent and can expand up to one hundred times its original volume Copyright UTeach Austin 2013
(http://www.youtube.com/watch?v=XCiDcJ9fqdo). There is also a substance called “magic sand” that contains hydrophobic properties (http://www.youtube.com/watch?v=-­‐1id-­‐gHQjbs). Hydrophobic means repelling and will not mix with water. For Elementary Students Any word that you could use to help describe something is called a property of that object. For example, you could say a piece of paper is white, rectangular, and bendable. You could measure its height, width, and thickness, and use a balance to determine its mass. All of these are properties of the piece of paper. These are all physical properties because you can determine these things without changing what the piece of paper is made of. The paper can be folded or torn, and these are also properties of the paper. Even though folding and tearing change the paper in some way, they do not change what the paper is made of, so they are also physical properties of paper. You can also describe paper by saying that it burns, but when you burn paper it isn't paper any more. Any property that results in changing the material into something else is called a chemical property. Properties are used to identify things and to sort or separate things. If frogs are green and toads are brown, you could identify one at a distance based on color, and you could sort a collection of frogs and toads based on color. If you had a box of golf balls and ping pong balls, you could separate them by throwing them in water -­‐-­‐ the golf balls will sink and the ping pong balls will float. Sink or float is another property of matter. Solubility (the ability of something to dissolve in something else), is another physical property. You can't tell just by looking at something new whether or not it is soluble in water -­‐-­‐ you have to test it with water to find out. Adding salt or sugar to water is an example of a mixture. A mixture is formed when two or more substances are added together but do not combine in any way. This means that the substances you started with are all still there in their original form. They are touching, but are not attached. There are two different kinds of mixtures, heterogeneous mixtures and homogeneous mixtures. In a homogeneous mixture, the components of the mixture are spread out evenly throughout the mixture and cannot be easily identified. Some examples of homogeneous mixtures are salt water, milk, smooth (but not chunky) peanut butter, ice cream, and gasoline. These are all made up of many ingredients, but because they are thoroughly mixed, the mixture is the same everywhere and appears to be a single substance. A homogeneous mixture is also called a solution. We'll talk more about those in a minute. (See Figure 1.) A heterogeneous mixture results when the components that make up a mixture are not evenly distributed and are easily identifiable. A salad or a box of assorted toys are two examples of heterogeneous mixtures. When sand is added to water it just sinks to the bottom, so sand in water is an example of a heterogeneous mixture. Mixing oil and water together creates two liquid layers that are easily identified, so that is also a heterogeneous mixture. If you Copyright UTeach Austin 2013
Figure 1: Heterogeneous and Homogeneous
stir a heterogeneous mixture (like oil and water) fast enough, it will start to look like a homogeneous solution, but if the components settle out on their own when allowed to sit undisturbed, the mixture is heterogeneous. Any time there are two distinctly different phases in a mixture, such as solid and liquid (sand in water) or two different layers of liquid (oil and water), the mixture is heterogeneous. (See Figure 1.) A solution is made up of a solvent and one or more solutes. The solvent is the substance doing the dissolving (for example, the water) and the solute is the substance being dissolved (the sugar or salt). Not all solutions are liquids. Mixing two gases is also a solution, and so is a metal alloy. In the case of two gases mixing, the solvent is considered to be whichever gas there is more of, so our atmosphere is a gas phase solution made up of oxygen, argon and various trace gases dissolved in nitrogen. The metal alloy brass is a solid solution of zinc dissolved in copper. Because mixing is a purely physical process, the components of the mixture can be recovered through a physical separation. The physical separation of two substances is always based on differences in the physical properties of those two substances, like with the frogs and toads, or the golf balls and ping pong balls mentioned earlier. Once a mixture has been separated into its individual components, the physical properties of each component can be used to help identify what it is. VII. Common Misconceptions • A heterogeneous mixture always appears in layers. Although a heterogeneous mixture may appear in layers, by definition a heterogeneous mixture is simply one that has substances unevenly distributed. For example, conglomerate rocks and sand at the beach is a heterogeneous mixture but may not appear in perfect layers. • Physical properties are human characteristics. Physical properties can be used to describe a substance. Physical properties include appearance, texture, color, odor, melting/boiling point, density, solubility, polarity, and many others. People also have physical properties -­‐-­‐ height, mass, volume, color, and so on, but when talking about people we generally refer to them as characteristics rather than properties. • Dissolving is a chemical property. When a substance is dissolved, it does not react with the solvent and therefore doesn't undergo a chemical change. The solute can be separated from the solvent and recovered its original form, such as evaporating the water from salt water to leave solid salt behind. The salt is still present as salt even when it is dissolved and you cannot see it. If you tasted the water (although we generally don't taste anything in the lab), you would still taste the dissolved salt. Background Information Sources: http://www.elmhurst.edu/~chm/vchembook/106Amixture.html http://www.elmhurst.edu/~chm/vchembook/104Aphysprop.html http://www.mcwdn.org/Physics/Magnetism.html http://www.teachersource.com/Chemistry/HydrophilicHydrophobicPolymers/WaterGelCrystals.aspx http://www.stevespanglerscience.com/experiment/00000082 Copyright UTeach Austin 2013
http://www.stevespanglerscience.com/product/instant-­‐snow VIII. Vocabulary List College Level Mixture: A combination of two or more substances that maintain their own chemical compositions when combined. Heterogeneous mixture: Two or more different substances that are mixed together unevenly and are not chemically combined. Homogeneous mixture: Two or more different substances that are mixed together evenly but are not chemically combined. Solution: A mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent). Solution is another name for a homogeneous mixture. Physical property: Any measurable property that can be observed without changing the chemical composition of the substance, such as appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity. Elementary Level Mixture / Mezcla: A mixture is a combination of two or more different things that don't bond together or change their individual composition when they are added together. They are touching, but are not attached. Heterogeneous mixture / Mezcla heterogenea: Heterogeneous mixtures are made up of two or more substances that are not mixed evenly. You can often see the individual components of the mixture. Homogeneous mixture / Mezcla homogenea: Homogeneous mixtures are made up of two or more components that mix together evenly and do not separate out after being mixed. Solution / Solucion: another name for a homogeneous mixture Solute / Soluto: the substance dissolved in a given substance Solvent / Solvente: usually a liquid substance that is capable of dissolving one or more other substances Physical property/propiedad fisica: A physical property is anything about an object that can be used to help describe it, but which doesn't require changing the substance into something else. Some examples of physical properties are appearance, texture, color, odor, melting point, boiling point, density, or solubility. IX. Safety considerations Before passing out materials: make sure students are clear that they may not smell or taste any materials nor perform any undirected experiments. Repeat throughout the lesson: Do not allow students to taste any of the materials. X. Question of the Day How can we identify substances in a mixture? Copyright UTeach Austin 2013
ENGAGEMENT Time: _3 minutes What the Teacher Will Do Probing Questions Hi everyone! I’m [outreach student name] and this is my teaching partner [outreach student name]. We will be coming each week to teach you science. At the beginning of each lesson, you’ll need to put everything away, except a pencil and your science notebook. Tell a little about your major or your research if you have done any or are intending to do any. First, I want to introduce our favorite spirit signal. When we want to get your attention, we will put our horns up, and say “Hook’em”, and that’s when we need your attention on us. So you’ll put your horns up and say “Horns!” Let’s Practice. “HOOK’EM!” Great! Now everyone should have everything put away with their eyes on us. Are you ready to be scientists with me? Teaching Tip: Show your attention signal and wait for all the students’ attention each time before you begin Student Responses Potential Misconceptions Horns! Copyright UTeach Austin 2013
ENGAGEMENT What the Teacher Will Do Probing Questions talking. Ask for attention once then wait. As you probably know research scientists from the University travel all over the world to do their work. We have one group of scientists that does research in the Arctic, while others explore rainforests, and still others that research tiny microscopic organisms in the oceans. Science is everywhere and so that’s where scientists go. One of the first things that scientists do is make observations. They observe things in order to determine properties. Let’s see if we can practice using our senses to make observations in order to figure out what is in each of these envelopes. We are going to pass around these three envelopes with different items in them. We want you to make observations about them without opening the envelopes. Pass around the envelopes with the pens and pencils, stapler and marbles and let the students feel what is 1.
Copyright UTeach Austin 2013
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Time: _3 minutes Student Responses Potential Misconceptions Where does science 1. A lab, in a school, on TV happen? Where might a scientist go 2. To the University, to the to do science? desert/rainforest etc., to the doctor’s office What do you hear? 3. Clinking What can you see? 4. Nothing ENGAGEMENT Time: _3 minutes What the Teacher Will Do Probing Questions inside without opening the envelope. After about 1 or 2 minutes, ask students to tell their observations and write them down on the board or doccam as they are said. Next show the students what is in each envelope. That was some great practice. Now today, we brought this package with us from the University. Show the envelope that has all of the vials in it and has a mailing address written on it that shows who it is being sent to and where it was sent from. We’re going to explore like real scientists and try to figure out what this is. This package says it’s from KIMP. MS. The UT post office had never heard of such a place so they called 911 and had a police K-­‐
9 unit sent in. The K-­‐9 unit cleared the package of any kind of explosive material so they took it to the chemical research lab at the University who determined that it wasn’t deadly or toxic. So since it was determined to be safe we brought it here to get your help to see what it is. Hold up one of the vials. 4. What does this vial look like? Student Responses Potential Misconceptions 4. Its pretty. It looks like sand art. Copyright UTeach Austin 2013
EXPLORATION What the Teacher Will Do Probing Questions Time: 30 minutes Student Responses Potential Misconceptions Please get out your interactive science journals. Make sure to copy down any important words we review today into your journals! The topic for today is “Mystery Package”. Write it on the board. Write that at the top of your paper. Pencils down and give me your attention. Today we are going to figure out what is in this vial. By the end of this lesson you should be able to answer the question of the day: How can we identify substances in a mixture? Show the question of the day to the students. 1. How can we go about 1. Look at each substance identifying the substances separately. Use a Some of you may think in this mixture? microscope or hand lens. observing the physical Test it. properties could help us. 2. What is a physical 2. Characteristics of property? something. Something you can observe with your senses. Post the “Physical Properties” poster. Here is a poster of some physical properties that you may recognize. Read the words on the poster. Pass out the role cards face down to the students. Call on a color to read their card out loud to the rest of their group. Blue cards, take a minute to read your job card aloud to Copyright UTeach Austin 2013
your group members. Continue until everyone has read their role to their group. Pass out worksheets. As I pass out worksheets, reporters should make sure everyone in their group has one. Let’s turn to the side of your worksheet that has a list of vocabulary. The first vocabulary word is mixture, which should be a review word. Post vocabulary word, mixture, on the doc cam. A mixture is when two or more substances combine and their chemical make up does not change. Fill in the word “mixture” for the correct definition Monitor students as they write. This will give you feel for their language level. Let’s look at your data table on the other side of your worksheet. You may use your senses of touch and smell to make observations about your materials as a group, but DO NOT taste any materials. Remember, as scientists, we don’t eat any lab materials. Copyright UTeach Austin 2013
3. How many substances is a mixture made of? 4. Does a substance change when it’s in a mixture? 3. Two or more! 4. No! It stays the same! You can use your hand lens to get a closer look! Also, remember lab safety! For this lab, it is okay to smell the substance directly, because we have determined that nothing is dangerous BUT, in all science labs you should use a technique called “wafting” when smelling any unknown substances. Demonstrate wafting to your students. Remember to wait for instructions before touching your materials. Remember, you may use your senses of touch and smell to make observations about your dry materials as a group, but do not taste any materials. Use your hand lens to get a closer look! Time/safety monitors make sure that everyone in the group is very careful with the materials and aware of where they are on the desk. If anything is knocked over, tell one of the teachers. The Technician needs to come up and get a tray for their group. Do not touch any of the materials once you are seated until we give you further instructions. Each tray should contain an ice cube tray or 6 cups labeled 1-­‐6, forceps, a bent paper clip, Copyright UTeach Austin 2013
and a vial that is a mixture containing Instant snow, sand, salt, magic sand, and pepper. Now I need the principle investigators in the groups to very carefully unscrew the cap to the vial and remove the cotton ball with the your fingers or the paperclip. Then, very carefully pour out the first layer into the cube or cup labeled “1”. Then set your vial on your tray or paper plate. Now, look back at your data table on your worksheets. We are going to do the first column together as a class and then move on. Everyone record the physical properties of the first layer on your worksheet in the first column. Allow about 1 minute for the first layer. Now that you know what we are doing, you will be pouring the rest of the layers out onto the ice cube tray or cups, one at a time, to observe each one's physical properties. Remove each cotton ball between each layer, put it next to the other one, and pour each layer out one at a time then record your observations. The next layer Copyright UTeach Austin 2013
5. What is one physical property of this layer? 5. It is small. Its white! should go in cube or cup “2”. The cotton ball helps separate the layers so we can observe the physical properties of each layer. Be sure to make your observations about one layer before you move onto the next one. Allow students approximately 8 minutes to complete this section. Students may need help taking out some of the cotton balls. Make sure to monitor students using probing questions #7-­‐10 to help them through the worksheet. Once everyone has the first column complete, continue. Now you will make predictions of how each layer will change when we add water to it. Think about if the substance will mix with the water, or if it will form a layer separate from the water. Make sure to be descriptive and don’t just write will get wet for your prediction. Most students will write “gets wet” for all predictions. Try to ask them Copyright UTeach Austin 2013
6. Why is there a cotton ball in between each layer? 7. What do you think that layer is? 8. What color is it? 9. What does it feel like? 10. What does it smell like? 6. The cotton separates the layers so we can identify each individual layer’s physical properties. 7. Instant Snow! 8. White! 9. Rough. 10. It does not have a smell. why or to describe what they mean. Once everyone has made their predictions in your group, then I will bring the water to you. You will use a pipette to slowly add the water. You will only add 2 pipettes full of water to each layer. Use your toothpick to mix each layer in the ice cube tray, and your spoon to scoop up the substance so you can get a better look. You may now begin making your predictions. Make sure all students have recorded their predictions, and then you may pass out the water. Ask each group if they know how to use the pipette. Demonstrate as you pass out the water as needed. As you pass out the water: Be sure to write down your observations on your worksheet under the “Observation in Water” column. You must complete observations of one layer before moving on to the next. Make sure the students are taking turns. Allow students approximately 5 minutes to complete this part. Use questions #12-­‐16 as a guide for discussing each layer. Copyright UTeach Austin 2013
11. How many pipettes of water will you add to each layer? 12. What change did you notice when you added water? 11. Two! 12. It separated from the water. After the students complete their worksheets and observe all the layers, pass out the “scientific” materials and properties list or post on doc cam. Now that we have observed the physical properties of each layer, we are going to compare them to the materials on the scientific list to see if they match any of our layers. This list was made by scientists at UT and has physical properties of different substances. We know that some of the items on the list are in the vial, but there are also some that are not. So be sure to look back at your physical properties and compare them to this list, then write the substance you think each layer is in the column that says, “What is this substance?” Help students read the Copyright UTeach Austin 2013
13. What happened when you mixed the water with the first layer? 14. What happened to the sand when you stirred it? 15. What happened when you stopped stirring? 16. Is the mixture evenly spread out? Or is it in layers? 13. It got wet. 14. It moved around and mixed with the water, but you could still see it. 15. It sunk to the bottom of the tray. 16. It isn’t even. I can still see the sand and the water. properties on the “scientific” list if needed. Assist them in identifying their layers. Let’s go over your answers. Be sure to call on different groups and different children. Layer 1: Instant Snow Layer 2: Sand Layer 3: Salt Layer 4: Magic Sand Layer 5: Pepper 17. What did you get for layer 17. Instant Snow! It was 1? Why? white and rough! 18. Were you able to identify 18. Yes! The scientific list of each layer? How? What properties matched mine! were they? EXPLANATION Time: 10-­‐15 minutes What the Teacher Will Do Probing Questions In the last column, we are supposed to identify which layer is homogeneous and which is heterogeneous. What does this mean? Let’s find out! In one bottle we have colored water and oil. In the second bottle we have colored water and sugar. Teacher one hold up the bottle with oil. Teacher two hold up the second bottle with sugar on the bottom. Great, so the oil and water 1. What do you observe about these two bottles/vials? 2. What are similarities between the bottles/vials? Student Responses Potential Misconceptions 1. The oil and water are in layers! The sugar is at the bottom. 2. They have layers. Copyright UTeach Austin 2013
EXPLANATION Time: 10-­‐15 minutes What the Teacher Will Do Probing Questions has layers and the sugar is sitting on the bottom, so they both have layers Shake both containers. Let the sugar dissolve. (Be sure it isn’t a saturated solution, so all of the sugar will dissolve) Don’t shake the oil and water too much or it will take too long to separate back out. Those are great observations! The materials in the bottles are examples of two types of mixtures -­‐ homogeneous and heterogeneous. Now these are difficult words, so let’s break them down. Now the first parts of the words are homo-­‐ and hetero-­‐. Turn your worksheets over to your vocabulary list. Homo-­‐ means the same and Hetero-­‐ means different. Write homo-­‐ = the same and hetero-­‐ = different. Record these on your worksheet. 3. What do you think will happen when I shake them? Turn and tell your partner what you think will happen. 4. What do you observe? What happened? Student Responses Potential Misconceptions 3. They will mix. No more layers. 4. There are still two layers. The sugar disappeared! There is still some sugar in the cup. Copyright UTeach Austin 2013
EXPLANATION Time: 10-­‐15 minutes What the Teacher Will Do Probing Questions Tape up the vocabulary sheet on the board or put it on the doc cam. Be sure you are recording the vocabulary words in your interactive notebooks. Heterogeneous mixtures are two substances that do not mix evenly. This means after mixing, the substances usually separate out. Point out on your worksheets which of the cups show a heterogeneous mixture. Have students point to this diagram on their worksheets. Substance 2
Substance 1
Now turn to a partner the student next to you and tell them what type of mixture the oil and water is and why. Allow a few seconds for the students to do this, ensuring that you walk around and monitor students. Ask students what answer they came up with. 5. Is the oil and water a Student Responses Potential Misconceptions 5. Heterogeneous mixture! Copyright UTeach Austin 2013
EXPLANATION Time: 10-­‐15 minutes What the Teacher Will Do Probing Questions Student Responses Potential Misconceptions 6. The oil and water make layers! Misconception: The heterogeneous mixture must be in layers. Truth: It is a mixture that is simply unevenly distributed. 7. Rice and Beans. A Salad. Right! The oil and water are not evenly distributed so it is a heterogeneous mixture. On the other hand, homogeneous mixtures do mix evenly and do not separate out after being mixed. An example of a homogeneous mixture is a solution! Everyone repeat solution with me. SOLUTION! A solution is where a substance is dissolved in a liquid. Record this in your vocabulary worksheet. Now, point out the cup on your worksheets that is an example of a homogeneous mixture. Have Students point to this diagram on their worksheets. Substance 1 and Substance 2 heterogeneous or homogeneous mixture? 6. How do you know that the mixture is a heterogeneous mixture? 7. What are some other examples of a heterogeneous mixture that aren’t in layers? Copyright UTeach Austin 2013
EXPLANATION Time: 10-­‐15 minutes What the Teacher Will Do Probing Questions Right, so the sugar and water is a homogeneous mixture. It is an example of a solution, because the sugar is dissolved in water. This means that the sugar and water are evenly distributed in the cup. When a substance is dissolved, it does not react with the solvent and therefore doesn't undergo a chemical change. The solute can be separated from the solvent and recover its original form, such as evaporating the water from salt water to leave solid salt behind. In the different layers we saw a mixture of substances that reacted differently to water. 8. Is the sugar and water a heterogeneous or homogeneous mixture? 9. How do you know that the mixture is a homogeneous mixture? 10. Is this a physical or a chemical property? Student Responses Potential Misconceptions 8. Homogeneous. 9. The sugar dissolved. You can’t easily separate them out. 10. Chemical! Physical! Copyright UTeach Austin 2013
Misconception: Dissolving is a chemical property. Truth: When a substance is dissolved, it does not react with the solvent and therefore doesn't undergo a chemical change. EXPLANATION Time: 10-­‐15 minutes What the Teacher Will Do Probing Questions Now, in the next column in our data sheet, we will circle which layer was homogeneous and which was heterogeneous when we added water. Walk around the room, and make sure groups are discussing. Ask questions #11-­‐12 to spur discussion. All these different materials have different physical properties that allow them to respond differently. A solution is an example of a homogeneous mixture but not all homogeneous mixtures will be solutions. So we figured out that a mixture can maintain the physical properties of each substance, which allowed us to identify them. Technician please place the 11. Which layers made homogenous mixtures when water was added? Why 12. Which layers were heterogeneous? Why? 13. So you saw that instant snow and salt were homogeneous mixtures. Are they both solutions? Why or why not? 14. Now let’s answer our question of the day: How can we identify substances in a mixture? Student Responses Potential Misconceptions 11. Instant snow and salt. It was evenly distributed. 12. Magic sand, pepper, sand. They stayed separate from the water and were not evenly distributed. 13. No. Salt is a solution when added to water, but instant snow isn’t. 14. We observed each layer's physical properties and figured out what they were. Copyright UTeach Austin 2013
EXPLANATION Time: 10-­‐15 minutes What the Teacher Will Do Probing Questions Student Responses Potential Misconceptions materials back in the bag and bring your cups or ice cube trays up to the front of the classroom. ELABORATION What the Teacher Will Do Probing Questions Time: 10 minutes Student Responses Potential Misconceptions Now we are going to pass out a small sample that has been separated from the mixture in our vial. This sample consists of two layers that got mixed up together. 1. Since they are mixed up, 1. A filter. does anyone have any idea of how we can separate them? A filter would be a great idea, but the substances look like they are about the same size. 2. What about a magnet? 2. If one were magnetic then How could we use a it would stick to the magnet to separate the magnet. layers? Right. We don’t know which layers are in this sample, but we can try it. Have the technician get plates with sand and iron mixtures and magnets. Everyone rub the magnet over the bottom of the petri dish while holding it. You can hold the magnet still and tilt the petri dish to the side. Copyright UTeach Austin 2013
ELABORATION What the Teacher Will Do Probing Questions Time: 10 minutes Student Responses Potential Misconceptions Demonstrate to the class if 3. What observations did you 3. Some black particles necessary. make when you placed the moved. Some stuck to the magnet near the mixture? magnet. 4. How could this be helpful to scientists who need to 4. They can use magnets! separate a mixture? They can tell the difference. Right! Magnetism is a physical 5. What are some other property of a substance. examples of physical properties for this 5. It’s brown, black, doesn’t mixture? smell, small particles, solid. Right, those are all examples of physical properties. Here is a list of some others. Hold up physical properties 6. Turn and talk with your list. Now let’s imagine that we shoulder partner and added water to our mixture. come up with answer to the question: How could 6. Use a filter. Use a magnet. we separate out the three substances in the mixture? 7. What physical properties would allow you to 7. Magnetism, size, states of separate the substances? matter (one is liquid) We could identify physical properties of each substance and think about how we could separate them. We could use a filter to separate the iron filings and sand from the water. Then we could use a magnet to separate the iron 8. What other physical filings from the sand. properties did we look at 8. Magnetism, Size, Color, today? Smell, Texture Copyright UTeach Austin 2013
ELABORATION What the Teacher Will Do Probing Questions The difference in the physical properties of substances in a mixture can be used to help separate them out. The two substances in the petri dish mixture are iron and sand. Iron is magnetic and sand is not. Therefore, a magnet separates the two when you place it near the mixture. Some mixtures, like homogeneous mixtures, are harder to separate. Show them the petri dish with salt water and the petri dish with salt left after evaporation. One way to separate some mixtures, like a salt and water mixture, is to boil the salt water. When you boil the salt water the water evaporates out but the salt stays on the bottom of the container! 9. Are there any other properties that could be useful to help separate them out of a mixture? 10. Are there other methods you know of that scientist might use to separate mixtures, like salt and water? Time: 10 minutes Student Responses Potential Misconceptions 9. Size: strainer, Density: oil and water layers, boiling point: Salt dissolved in water 10. They can evaporate it! Use a coffee filter. EVALUATION Copyright UTeach Austin 2013
Time: 10 minutes What the Teacher Will Do Probing Questions We have determined how to identify substances of a mixture as a group of scientists. It is also important that scientists make reports and write down what they have done for the day. Now we will give you an opportunity to show us what you know. Hand out Show off what you know to the each student. Once students have completed answering questions on their own, discuss answer choices asking questions 1-­‐4. Remember this is also an important part of being a scientist! If time permits, continue with the journal prompt or use it as a class discussion. Journal Prompt: In your interactive journals, explain how you would separate each substance in a mixture containing water, rocks, salt, and paper clips. Copyright UTeach Austin 2013
Student Responses Potential Misconceptions Physical Properties Size B oiling p oint Color Solubility Smell M
agnetic Texture Density Melting point Taste Question of the Day: How can we identify substances in a mixture? Copyright UTeach Austin 2013
Important Vocabulary Mixture/Mezcla: When two or more substances are combined and their chemical make-­‐up does not change. Heterogeneous mixture/Mezcla heterogénea: Two substances that do not mix evenly. Homogeneous mixture/ Mezcla homogénea: Two substances that mix evenly and do not separate out easily after being mixed. Solution/Solución: A type of homogenous mixture where one substance dissolves in another. Journal Prompt Explain how you would separate each substance in a mixture containing water, rocks, salt, and paper clips. Copyright UTeach Austin 2013
Mystery Package Materials List Substance Physical Properties Small, round particles; repels water, Magic Sand brightly colored Instant Snow White, small, round, absorbs water White, small, sparkly particles, will Salt dissolve in water Black and white, small particles, Pepper strong smell Brownish tan color overall, small Sand and round Copyright UTeach Austin 2013
Name: _______________________________ “Mystery Package” Observation Sheet Layers Physical Properties Prediction Observation Substance (of what will in water happen in water) 1 2 3 4 5 6 Copyright UTeach Austin 2013
Homogeneous or Heterogeneous (circle one) Homogeneous or Heterogeneous Homogeneous or Heterogeneous Homogeneous or Heterogeneous Homogeneous or Heterogeneous Homogeneous or Heterogeneous Homogeneous or Heterogeneous Name: __________________________________ “Mystery Package” Vocabulary A __________________ is a combination of two or more substances that maintain their own chemical compositions when combined. _________________ = the same _________________ = different A _____________________ is two substances that do not mix evenly. A _____________________ is two substances that mix evenly and do not separate out easily after being mixed. Substance 1 Substance 2
and Substance 2 Substance 1
____________________________ ___________________________ A ________________ is a type of homogenous mixture where one substance dissolves in another. Copyright UTeach Austin 2013
Name____________________________________________ Show What You Know! 1. Which of the following is an example of when two substances mix evenly but do not separate out easily after being mixed? a. Sand and water b. Salt and water c. Rocks and water d. Cotton ball and water 2. Which of the following is NOT a physical property? a. Color b. Density c. Dissolving d. The chemical make up Solubility
3. Based on the graph to the right, which of the Solubility of Sugar and Salt
following will dissolve the fastest or has the highest solubility at 70˚C? a. Salt b. Sugar c. Both d. Neither 4. You have a bowl of unknown objects and you are given a list of the physical properties of the objects. You know that in the bowl there is a magnet, some ping pong balls, some rocks, and some salt. How can you separate the ping pong balls from the other objects? a. Boil the bowl of objects b. Put a magnet near the bowl c. Drop the objecting into a funnel d. Dump the objects into a bucket of water Copyright UTeach Austin 2013