Lesson Plan: Mystery Metals

Transcription

1 Lesson Plan: Mystery Metals Summary In this lesson, students will make measurements, calculations, and inferences to help solve a mystery about Created by: 2014 AACT Elementary School Content Writing Team the identity of an unknown metal. After being presented with a scenario about a fire along with some evidence from the fire, students will be challenged to determine the temperature of the fire. They will calculate the density of various metals and then use the periodic table to identify them. They will then compare melting points of the metals and use this information to infer the temperature of the fire. Resource Type Lesson plan Grade Level Elementary school Objectives By the end of this lesson, students should be able to: Measure the weight or mass of a substance. Measure the volume of a substance using the water displacement method. Calculate the density of a substance. Use the periodic table to identify a substance based on its density. Gather information from the periodic table. Infer the temperature of a fire based on knowledge of the melting point of metals. Chemistry Topics This lesson supports students understanding of the following topics in chemistry: Matter Elements Atoms Melting point Density Time Teacher Preparation: First use of curriculum, 1 hour; subsequent years, 10 minutes. Lesson: (Note: The amount of time required for each part of the lesson will depend on your students prior knowledge and on how they choose to present their results.) Engage: 20 minutes Explore 1: minutes Explore 2: minutes Explore 3: minutes Explore 4: 30 minutes Explore 5: minutes

2 Explain: 60 minutes Materials Set-Up: Metal strips: iron, zinc, tin, aluminum, lead, nickel, and copper (can be ordered from a science supply company) Propane torch Engage Firefighter (s) (or one or more people acting as firefighters) Metal strips, some melted, some not o Melted: zinc, tin, aluminum, and lead o Not melted: iron, nickel, copper Mystery metals Receipt Explore Metal strips from Engage Periodic Table that contains information on density and melting point Optional: objects of various densities Scale or balance Graduated cylinder Water Thread Pencil, colored pencils Graph paper or Science Journal Safety Preparation: Use caution when using the propane torch to melt the metal samples. Metal can sometime sputter causing small amounts to jump from the vicinity of the torch that can burn skin or material surrounding the work area. Leather gloves, shirts with long sleeves, and safety goggles should be worn. Have students wash their hands after handling the metal strips. Although this activity is specifically designed with no safety issues, activities like this provide an opportunity to introduce lab safety to students. Forensic specialists make a practice of using safety goggles, rubber gloves, and rubber aprons. Vocabulary Terms Physical change Density Melting Point Keywords periodic table, element, metal, density, melting point, properties, forensics Teacher Notes Preparation

3 1. Order strips of iron, zinc, tin, aluminum, lead, nickel, and copper from a science supply company. 2. Using a propane torch, melt the zinc, tin, aluminum, and lead strips (separately) in an iron bowl. Allow to cool. (After you have prepared the necessary samples, you can store them for follow on years.) Logistics and Tips This activity is easily adaptable to fit the number of metal samples you have. You can conduct the activity with a single set of metals (dividing the single set among 4 groups 2 samples each) or provide a full set of samples to each small group to analyze. This activity is best done after students have some familiarity with the concepts of mass, volume, density, and melting point. However, it can also be used as an introduction to these concepts. If the ideas and methods are new to your students, plan to spend more time guiding them through each step of the Explore activity. It is not necessary for students to understand the concept of an element yet. However, if they do, make it clear that the metals they are investigating are pure elements. This is why the periodic table of elements can be used to identify them based on density. (If the metals were compounds or mixtures, the periodic table would not help.) When measuring volume using water displacement, have students tie a piece of thread around the end of each metal sample and dip it into the water by the thread. The purpose of this is to allow the students to submerge the sample and then pull it out easily. Differentiation The lesson can be simplified by o bypassing exploration and use of the periodic table and simply giving students the simple table of properties provided below. o reducing the number of types of metal strips examined. Using even just a single metal can help narrow down the temperature of the fire. o telling students directly what to do, rather than guiding them to figure it out themselves Students who have experience calculating density should be encouraged to help plan the investigation. Science Background Density In this activity, students identify metals based on density. Density is an intrinsic property of a material: it is the same regardless of the amount of material present. Density is a measure of the amount of matter in a given unit of volume. In general, density is measured in grams per cubic centimeter (g/cm3) and is calculated by dividing mass by volume. The densities of the metals examined in this lesson are given in the table below.

4 Measuring Volume: Water Displacement Method The mass of a sample is easily measured using a scale or balance. Volume, however, can be trickier if the sample is not a regular geometric shape. In this activity, students use the water displacement method: a) Fill a graduated cylinder with water ½ to 2/3 full, to an even marking on the cylinder. Record the level of the water. b) Place the sample in the cylinder. Measure and record the new level of the water. c) Subtract the first reading from the second reading. This is the volume of the object. Note that volume in a graduated cylinder is generally given in milliliters (ml). One milliliter is the same as one cubic centimeter (cm 3 ). It is important to make sure that students understand why this method works: the object is displacing a volume of water that is equal to its own volume. The total volume in the cylinder is the starting volume of the water plus the volume of the object. Sample Volume of Water Volume of Water + Sample Volume of Sample A 20 ml 24 ml 24mL 20 ml = 4 ml = 4 cm 3 Melting Point Once students identify each metal based on its density, they use the periodic table to find the melting point of each metal. The melting point is the temperature at which the metal melts. Each metal has a different melting point. If the students know what the melting point of the metal is and then examine the metal to see whether or not it melted in the fire, they can infer whether the fire temperature was greater or less than the metal s melting point. The melting point of each metal is also given in the table below. Periodic Table In this activity, students use the periodic table to find out the density and melting points of various metals. You can use your own periodic table or have students use the American Chemical Society s online periodic table. To use the ACS periodic table, click on the element of interest to bring up more information. The density and melting point can be found in the physical tab. Note that the melting point is given in kelvins. Explain to students that the Kelvin Scale is a temperature scale like the Celsius scale and the Fahrenheit scale. To convert to degrees Celsius, simply subtract 273. Properties of the metals used in this activity: Metal Symbol Density Melting Point Nickel Ni 8.9 g/cm 3 1,728 K Tin Sn 7.3 g/cm K Iron Fe 7.9 g/cm 3 1,811 K

5 Aluminum Al 2.7 g/cm K Lead Pb 11.3 g/cm K Copper Cu 8.95 g/cm 3 1,358 K Zinc Zn 7.1 g/cm K Note: For this investigation, students must assume that the metal strips are pure metals. Some astute students may point out that requiring this assumption is a flaw in the investigation. Additional Resources Simply Science-Atoms by Melissa Steward; The Properties of Solids by Marylou Morano Kjelle Elements of the Periodic Table by Suzannne Slade Lesson Engage 1. A knock comes on the door immediately followed by the entry of firefighters. One is holding a clear container containing mystery metal samples. The firefighters explain that they have just returned from the scene of a fire and have collected some evidence. We found these metal strips at the scene. We think they could help us find out more about the fire. The firefighters also explain that they don t know what each metal strip is made of, but they did find an on a computer at the scene. The was a receipt for metal strips, which could be useful. The firefighters explain that they need to class to help them figure out how hot the fire got. Can we get your help? The firefighters depart, leaving the evidence with the class. 2. Discuss with the class what the task is (determining the temperature of the fire), and how they might go about accomplishing it. a) What do we know? [There was a fire. Some metal strips were at the scene.] b) What evidence do we have? [We have the metal strips. We have a receipt for metal strips.] 3. Pass around the container of metal strips and allow students to make some initial observations. Safety Note: Explain to students that feeling, smelling, and tasting unknown substances is not a safe practice. Students should refrain from putting hands in their mouths while handling materials. Make sure students wash their hands after handling the metal strips. a) Describe what you see: shape, color, any other characteristics? b) Are all of the strips the same? If not, how are some different? [students should notice that some are melted and others are not; they may also notice differences in weight (due to differences in density) or flexibility]

6 4. Pass around the receipt for students to examine. What is the receipt for? How do you think it is related to the other evidence we found? Guide students to recognize that the receipt is for metal strips like the ones found at the scene. The receipt is for metals that are elements. It is likely that the metals at the scene are these elements. We just don t know which is which. 5. Have students turn and talk to brainstorm ways of figure out how to use the metal strips to determine the temperature of the fire. Then come back as a group to discuss the problem. Guide students with questions like o What happens to some substances in a fire? [they burn or melt] o Why do you think some of the metal strips melted and some did not? [some have a lower melting temperature than others] o How can we figure out what the melting temperature of each of these strips is? [heat them up and measure the temperature at which they melt; find out what metal each is made out of and use the periodic table to find out the melting point] o How will knowing the melting temperature of each strip help us figure out what temperature the fire was? [the fire must have been as hot as the melting temperature of the metal strips that melted, but not as hot as the melting temperature of the metal strips that did not melt] 6. As a group, work together to plan the investigation. Student will have various ideas. The steps below will work well: a) Measure the mass and volume of each strip, and calculate its density. b) Use the periodic table to determine the density of the metals on the receipt. c) Identify the metal that each mystery strip is made of by matching it to the metal on the receipt, based on density. d) Use the periodic table to determine the melting temperature of each strip. e) Figure out the lowest temperature the fire could have been by examining the melting temperature of the strips that melted. (The fire must have been at least this hot.) f) Figure out the highest temperature the fire could have been by examining the melting points of the strips that did to melt. (The fire could not have gotten this hot.) Explore 1. Properties and the Periodic Table If necessary, begin by introducing or reviewing the properties of density and melting point. Make sure students understand the following: Density is a measure of the amount of matter in a given amount of space. You may wish to have students feel substances of different densities. It may be instructive, for example, to have them sort the metal strips according to density, based on how they feel.) A pure solid (an element like iron) has the same density regardless of its size and shape.

7 Density is measured as mass per unit volume, generally grams per cubic centimeter. Density is calculated by measuring the mass in grams, the volume in cubic centimeters, and then dividing mass by volume: Melting point is the temperature at which a solid substance melts and turns liquid. (It is the same as the freezing point, the temperature at which the liquid turns solid.) The melting point of a substance is the same, no matter how much of the substance there is. Different substances have different melting points. You may want to give students examples: the metal mercury is liquid at room temperature while iron is solid. Thus they must have different melting temperatures. The Periodic Table shows all of the known elements, including the metals that are being investigated. For each element, the periodic table includes important information, including density and melting point. 2. Data Collection Have students figure out what data they need to collect or calculate, and how it should be displayed. The following table will work well. Before beginning data collection, have students explain where/how they will get each data point. Metal Property How I will find out General observations Looking, feeling Melted or unmelted? Mass (grams) Volume (cubic centimeters) Density (g/cm 3 ) Identity (what metal is it?) Looking, feeling Use a balance Put in water Calculate Compare to density of a known

8 Melting Point (K) metal Look on the periodic table 3. Calculating Density Have students calculate the density of each mystery metal, recording measurements in their data tables as they proceed. a) Use the balance or scale to find the mass of each sample in grams. b) Use the water displacement method to measure the volume of each sample. (see Teacher Notes) c) Calculate the density of each same by dividing mass in grams by volume in cubic centimeters (milliliters). 4. Identifying the Metals Have students use the periodic table to identify each metal based on its density. a) Look up the density of each metal listed on the receipt found at the scene of the fire. b) Match the metals on the receipt with the mystery metals. 5. Identifying Melting Points Now that they know the identity of each metal strip found at the scene, students can use the periodic table to find out the melting point of each strip. Explain 1. Narrowing Down the Fire Temperature Students now have enough information to infer the minimum and maximum temperature of the fire. Challenge students to figure out how to do this. One way is to make a bar graph showing each metal s melting point. Arranging the metals in order by melting point and color coding them according to whether the strips were melted or not will allow everyone to see clearly the minimum and maximum temperature of the fire. Element Melting Point (K) Tin 505 Lead 600 Zinc 693 Aluminum 933 Copper 1,358 Nickel 1,728 Iron 1, Make and Support a Claim Students are now ready to state their claim about the temperature of the fire. Students can do this in any number of ways. Possible methods include: A report to the fire chief presenting the findings A newspaper article reporting about the fire investigation A TV news video about the fire investigation

9 No matter what form the report takes, it should include description of the methods, all of the data, and the reasoning behind the conclusions. Elaborate Students can extend what they ve learned in a number of ways. For example: Forensic Science Have students find out more about how fires are investigated. What questions do investigators try to answer? What types of evidence do they collect? How do they analyze the evidence? Electrical Engineering Select the resistance setting on a digital voltage ohm meter (VOM). Connect the common line (black) to one end of the metal strip sample while attaching the positive test lead to the VOM (red) to the opposite end. The number displayed is a resistance in ohms. This value should be different from one metal to another. How could we use electrical resistance to identify a metal? Model Atoms of Metal Strip Sample Have students construct atomic models of the metals, including protons, neutrons, and electrons using styrofoam balls, stick pins, or bamboo skewers, Evaluate Students can be evaluated formatively throughout the lesson with questioning, and summatively with the final report. In addition, you may want to use the following items. Multiple Choice Items 1. Platinum is an element. Avron has two cubes of platinum of different sizes. The density of the larger cube is about 21 grams per cubic centimeter. What is the density of the smaller cube most likely to be? 1. About 21 g/cm 3 * 2. Less than 21 g/cm 3 3. More than 21 g/cm 3 4. It is impossible to predict 2. DaShawn has left containers of antifreeze, castor oil, water, and rubbing alcohol outside overnight. He notices that in the morning, the water and the castor oil are solid, but the antifreeze and the rubbing alcohol are still liquid. The melting temperatures of the four substances are shown in the table. Substance Melting Temperature Antifreeze C Castor Oil -9.8 C Pure water 0 C Rubbing Alcohol -89 C Based on this information, what could the temperature have been outside? a. 10 C b. -5 C c. -11 C*

10 d. -50 C Discussion Questions 1. When the house fire melted some of the samples, was the change the samples experienced physical or chemical? How do you know? [The change the metal samples went through was physical. The samples just changed state, from solid to liquid. The atoms did not change.] 2. Why do you think different elements have different densities? [Students should be able to infer that different elements have different amounts of matter in them. In fact, different elements have different numbers of protons and neutrons (which make up the bulk of their mass). They may also infer that the atoms in one elemental substance are packed more tightly together than the atoms in another.] 3. What are some other ways that a scientist could identify the metals found at the scene? [Students may know that there are other properties that could be used, such as electrical conductivity and melting point. They may also know that there is scientific equipment that can analyze the elemental make-up of substances.] 4. How sure are you that your conclusions are correct? What assumptions did we have to make to carry out this investigation? [We had to assume that the strips were pure elements. If they were compounds or mixtures, we would have come to the wrong conclusions. We assumed that the receipt showed the possible metals that could be there, but maybe there were other possibilities.] Cross-Disciplinary Extensions Connect to Math Have students put the metals in order by density and calculate the difference in density between various metals. How much denser is lead than aluminum? Why do you think aluminum is used rather than lead to build airplanes? Have students use density to calculate volume or mass, given the value of the other. For example, If you have a piece of aluminum that has a volume of 1 cubic centimeter, what is its mass? (2.7 g/cm 3 1 cm 3 = 2.7 g) Connect to Reading, Writing, and Social Studies Have students research a particular metal found at the scene of the fire. What is the metal used for? What important properties does the metal have that make it useful? Where is it found on Earth? How is it mined? Next Generation Science Standards This lesson supports the following: Practices of Science and Engineering Asking questions and defining problems Planning and carrying out investigations

11 Analyzing and interpreting data Engaging in argument from evidence Using mathematical and computational thinking Obtaining, evaluating, and communicating information Cross-Cutting Concepts Cause and Effect: Mechanism and Explanation Energy and Matter: Flows, Cycles, and Conservation Stability and Change Disciplinary Core Ideas, Grades 3-5 Physical science The amount (weight) of matter is conserved when it changes form, even in transitions in which it seems to vanish. (5-PS1-2) Measurements of a variety of properties can be used to identify materials. (5-PS1-3) Chemical Reactions No matter what reaction or change in properties occurs, the total weight of the substance (s) does not change (5-PS1-2) Engineering Design Research on a problem should be carried out before beginning to design a solution. Testing a solution involves investigating how well it performs under a range of likely conditions. (3-5-ETS1-2) At whatever stage, communicating with peers about proposed solutions is an important part of the design process, and shared ideas can lead to improved designs. (3-5-ETS1-2)