Physical and Chemical Properties of Materials 40- to 2 50-minute sessions ACTIVITY OVERVIEW 14 L A B O R ATO R Y Students explore the properties of a wide variety of materials and examine the relationship of these properties to the uses for the materials. They examine physical properties that include; color, transmission or absorption of light, density, flexibility, and hardness. They also examine a chemical property; reactivity with an acid. Students then determine an appropriate material for several products. KEY CONCEPTS AND PROCESS SKILLS (with correlation to NSE 5 8 Content Standards) 1. Substances have characteristic properties, such as density and ivity, that are independent of the amount of the sample. (PhysSci: 1) 2. Substances are often placed in categories or groups if they react in similar ways; metal is an example of such a group. (PhysSci:1) 3. Students use appropriate tools and techniques to gather, analyze, and interpret data. (Inquiry: 1) KEY VOCABULARY chemical property density material physical property B-27
Activity 14 Physical and Chemical Properties of Materials MATERIALS AND ADVANCE PREPARATION For the teacher 1 large strip of each of the following: aluminum copper iron Formica polystyrene plastic 1 large version each of a: piece of ceramic tile block of wood glass rod piece of granite piece of limestone carbon rod 1 Transparency 14.1, Categories of Materials * 1 overhead projector * water For each group of four students 1 270-mL (9-oz.) plastic cup 1 stir stick 1 glass scratch plate 1 battery harness and lightbulb * 1 9-volt battery 1 15 ml dropper bottle of 1M hydrochloric acid 1 strip each of: aluminum copper iron Formica polystyrene plastic 1 piece of ceramic tile 1 piece of wood 1 glass rod 1 piece of granite 1 piece of limestone 1 small carbon rod * water * paper towels B-28
Physical and Chemical Properties of Materials Activity 14 For each student: 1 Student Sheet 14.1, Properties of Materials (optional) 1 Group Interaction Student Sheet 2, Developing Communication Skills (optional) * 1 pair of safety goggles *Not supplied in kit Group Interaction Student Sheet 2 can be found in Teacher Resource II: Diverse Learners. For easy distribution, prepare sets of materials for each group of students. You might place each set in a clear zipper-lock sandwich bag. Group Interaction Student Sheet 2 is in Teacher Resources II: Diverse Learners. The metals - copper, iron and aluminum - will take time to display signs of a chemical reaction with the 1M HCl. Set up this demonstration before class so that students will observe evidence of a reaction in one class period. SAFETY Safety eyewear should be worn in this activity. Stress to students that they must use care in handling the materials. If they cannot easily flex a material with gentle pressure when they test it, they should add no pressure that could break or tear it. Tell students to avoid contact with sharp edges. It is recommended that students wear protective plastic gloves when working with caustics, such as hydrochloric acid. Note, however, that the concentration that is used in this activity is low enough that wearing gloves is not imperative. Check your school s and district s safety requirements to determine if you will provide them in this activity. TEACHING SUMMARY Getting Started 1. The class discusses common materials and their uses. Doing the Activity 2. Students explore some properties of common materials. 3. Students sort materials based on their properties. 4. The class discusses the results of the investigations and compares categories. Follow-Up 5. Students choose materials for several products.if this works) B-29
Activity 14 Physical and Chemical Properties of Materials BACKGROUND INFORMATION Categories of Materials used in this Activity Four of the materials used in this activity are pure elements. Aluminum, copper, and iron are metallic elements, while carbon is nonmetallic. Students will be formally introduced to elements in Activity 15, Families of Elements. Three of the materials used in this activity the plastics, Formica, and limestone are compounds, and each is a different compound. Limestone is a form of the compound calcium carbonate. Wood, granite, glass, and ceramic tile are mixtures of a number of compounds. For example, wood contains cellulose and other compounds, while granite contains a variety of minerals, including silicon dioxide and several silicates. Ceramics, including glass, are mixtures of materials fused at a very high temperature and then cooled. Synthetic Materials Although natural glass, such as obsidian, and natural plastics, such as amber and horn, exist, plastics and ceramics are two of the major categories of synthetic materials. Plastics are made of very large molecules that are polymers of many smaller units called monomers. They are discussed in more detail in the Background Information for Activity 19, Properties of Plastics. Ceramics are a broad class of materials that include pottery, glass, tile, concrete, and cement. They are manufactured by processing inorganic raw materials, such as sand or clay, at high temperatures. Ceramics are generally hard and brittle. B-30
Physical and Chemical Properties of Materials Activity 14 TEACHING SUGGESTIONS GETTING STARTED 1. 1. The class discusses common materials and their uses. Tell the class that in this activity they will investigate a large variety of materials to understand how the properties of materials determine their uses. This will broaden the discussion they began in Activity 12, Evaluating Materials, on plastic, aluminum, and glass for drink containers. Ask them to recall the properties of the three materials they considered, such as cost, convenience, and recyclability. Remind them also of the product life cycles they constructed in Activity 13, Product Life Cycle, and of the useful-life stage of the product. Explain that materials engineers work to improve materials to make them better suited for their intended purpose during their useful life. DOING THE ACTIVIT Y 2. Students explore some properties of common materials. Hand out a set of materials to each group. As you hold up your large pieces of the materials, identify them, and have students find the corresponding ones in their sets. Stress to students that because they and other classes will be using these materials in several activities they must not to break any of them. Point out that the carbon rod is easily broken. Check to see that students understand the term property, and, if necessary, remind them that a property is a quality or trait that characterizes a material or object. Scientists frequently distinguish between physical and chemical properties of substances. Physical properties can be determined without seeking a chemical reaction. Chemical properties can only be determined by adding another chemical to see if a reaction occurs. Explain that a chemical reaction takes place when one or more substances change chemically into another substance or substances. When this happens, scientists say that the substances react. For example, in Unit A, Studying Materials Scientifically, students observed that some metals react with acid. Discuss some examples of physical and chemical properties. Point out that computer paper is white, translucent, creases or crumples when folded, and tears easily; these are all physical properties of a certain kind of paper. Paper when ignited also combines with oxygen in the air in the chemical reaction called combustion. This is an example of a chemical property. A chemical property can be determined only by mixing a substance with another substance and observing whether and how it reacts. A chemical property of iron is that it rusts in the presence of water and oxygen. Remind students that in Unit A, Studying Materials Scientifically, they investigated such physical properties as density and electrical ivity. Tell them that in this activity they will investigate these additional physical properties: Color: Does it resemble the color of something else? Hardness: How resistant to scratching is it relative to another substance? Luster: How is light reflected from the material? Is it shiny, dull, metallic, glassy, waxy, etc.? Light transmission: Does light pass through the material? Texture: How does the material feel between the fingers? Is it gritty, smooth, etc.? Flexibility: Does the material bend with gentle pressure? And one chemical property: Reaction with hydrochloric acid: Does it react? In Unit A, students investigated the chemical properties reactivity and corrosiveness. In this activity they will investigate only one chemical property reactivity with hydrochloric acid. Make sure students understand the terms listed above; they will appear throughout the activity. You B-31
Activity 14 Physical and Chemical Properties of Materials might review them with the class by discussing the properties of paper as an example, since it is a material that won t be studied in the activity. During this introductory discussion, be sure to point out that the objects in the sets of materials have different shapes. Some are strips (iron, copper, polystyrene plastic, and melamine plastic); others are blocks (tile and wood); and still others are cylinders (carbon and glass). Two others are irregularly shaped (granite and limestone). The reasons for this are practical these are shapes that are easily and inexpensively obtained. Each material, however, can be produced in any shape. Therefore, shape cannot be used to classify materials and is not a physical property of a material. Ask students to give some examples of familiar shapes of the materials, such as metal rods (wires and nails), and glass strips or sheets (microscope slides and windows). With the class, review the testing procedures as explained in Table 1, Testing Physical and Chemical Properties. Discuss with students the importance of having an organized method of recording their observations during their investigations of the properties of each material. In Procedure Step 2, students construct a data table in their science notebooks. If they need guidance in constructing the table, pass out copies of Student Sheet 14.1, Properties of Common Materials. Have groups perform the tests and record their results. A completed version of the table appears below. Note that the metals will react with the 1M HCl in time. Set up this demonstration before class so that students will see evidence of a reaction in the time of one class period. Sample Answers, Student Sheet 14.1 Testing Physical and Chemical Properties Material Name Color Light transmission Luster Texture Flexibility Hardness versus glass Electrical ivity Density relative to water Reaction to Hydrochloric Acid Aluminum Silver Opaque Brilliant Smooth Very Softer Conducts More Yes (over time) Carbon Black Opaque Dull Smooth Not Softer Conducts More No Copper Reddishbrown Opaque Brilliant Smooth Very Softer Conducts More Glass Colorless Translucent Glassy Smooth Not Same Granite Speckled black and pink Opaque Dull Gritty Not Harder More More Iron Gray Opaque Brilliant Smooth Very Harder Conducts More Limestone Brown Opaque Dull Gritty Not Harder Formica Gray Opaque Dull Smooth Somewhat Polystyrene plastic White Opaque Dull Smooth Somewhat Softer Softer More More More Yes (over time) No No Yes (over time) Yes No No Tile White Opaque Dull Rough Not Harder More No Wood Tan/brown Opaque Dull Smooth Not Softer Less No B-32
Physical and Chemical Properties of Materials Activity 14 3. Students sort materials based on their properties. As student groups finish the tests, Procedure Step 3 asks them to sort the materials they tested into groups based on their properties. Each group of materials must have one, two, or more properties in common. Look for patterns in the groupings. For example, Metals: exhibit a shiny metallic luster. are flexible. are opaque. are cold to the touch. usually sink in water. react with hydrochloric acid Nonmetals: vary in color and texture. float or sink in water. may or may not be flexible. may range from transparent to opaque. Give student groups time to discuss their choices and to come to a consensus. You might hand out Group Interaction Student Sheet 2, Developing Communication Skills, to encourage productive discussion. Model and provide guidance as to how agreement and constructive disagreement look and sound. As they work with their group, students should record the components of each category in their science notebooks and create a title for each. 4. The class discusses the results of the investigation and compares categories. Have groups present to the class how they arranged the materials by properties. Groups of students who disagree about the properties of any material to revisit their records again to see if they can come to an agreement. They need not, however, come to an agreement about how they grouped the materials, because Analysis Question 1 asks them to consider differences in categories. Emphasize that there is more than one reasonable way to sort, as long as it is based on properties of the materials. For example, one group may have chosen to separate the materials into metals and nonmetals, while another created a separate category for rocks. Suggest to students that one way the materials can be categorized is by their raw materials and how they are made. Show Transparency 14.1, Categories of Materials, and discuss the definition of each category. Explain that the categories provided are only one way to group the materials, and are very loose definitions of what each category entails. There are other possible groupings. For example, the metals may also fit in the natural category. One possible way to group the materials follows: the ceramics are glass and ceramic tile; metals are aluminum, copper, and iron; plastics are Formica and polystyrene; and natural materials are carbon, granite, limestone, and wood. Be sure to stress that this is only one way to sort the materials. Give students a chance to discuss Analysis Questions 2 and 3 in their groups, and then ask for their responses. Review the definition of property if necessary. During the discussion students should develop the concept that shape is usually a property of the object, not the material. (An exception would be the shape of a crystal, such as a salt crystal.) Color, on the other hand, may or may not be a property of a material. For example, copper has a characteristic color, but plastics can be produced in all sorts of colors. FOLLOW- UP 5. Students choose materials for a variety of uses. Analysis Questions 2 and 3 focus on differences between the properties of an object and the properties the material is made of. Analysis Question 4 has students suggest materials for several products. Their responses to this question will indicate whether they understand the relationship between properties and uses of a material. B-33
Activity 14 Physical and Chemical Properties of Materials SUGGESTED ANSWERS TO QUESTIONS 1. Were your groupings the same as those of the other students? If they were different, explain how. Answers will vary, and students should realize that there were different ways to sort these materials, depending on the properties each group chose to consider. 2. Should the shape of an object be considered a property of the material? Explain. No, the shape of an object is the property of the object, not the material. The same material, like plastic, can be made into many different shapes. 3. In this activity, you recorded the color of each material. Think of and explain two cases in which color does not help identify a material. Some materials have a distinctive color, such as metals, but many other materials such as plastics and glass, can be produced in a variety of colors. Plastic is another material that can be dyed in any color. So knowing the color of the plastic does not automatically indicate which plastic it is. 4. In your science notebook, make a copy of Table 2, Selecting Materials for Products, shown below. For each product listed in the first column, complete the table by listing one material that you tested that would work well and one that would not work well. Explain your reasons for each choice in the appropriate column. Sample Student Results for Table 2, Selecting Materials for Products Use of material Material that would work well Reasons Material that would NOT work well Reasons Electrical wire Copper, iron Conducts electricity Plastic, wood It does not electricity. Garden statue Granite Strong, attractive, and not reactive Limestone It would scratch easily. Toy boat Plastic Plastic can be flexible and resists breaking. And it won t be damaged by water. Glass It may break and be dangerous. Tabletop Most of the materials can be used for a tabletop. Most of the materials can be used for a tabletop, because they are fairly hard. Carbon It breaks easily. Inexpensive container for an acid, such as vinegar Glass It does not react with acid, and you can see through it to find out when you will run out. Aluminum, or iron These react with acid. B-34
Categories of Materials Ceramics Metals Plastics Natural Hard, brittle Usually shiny solids Chemical compounds Materials that are materials that are that heat or usually made from found in nature. formed by heat. electricity and can petroleum products. usually be formed Plastics can be into sheets and molded into various drawn into wires. shapes. 2007 The Regents of the University of California Issues and Physical Science Transparency 14.1 B-35
Name Date Testing Physical and Chemical Properties 2007 The Regents of the University of California Material Name Color Light Transmission Aluminum Carbon Copper Glass Granite Iron Limestone Formica Polystyrene plastic Tile Wood Luster Texture Flexibility Hardness versus Glass Electrical Conductivity Density Relative to Water Reaction to Hydrochloric Acid Issues and Physical Science Student Sheet 14.1 B-37