Sci-Tech. Connections. The Heat's On. Hot Potatoes Grade 7 Sampler

Transcription

1 Sci-Tech Connections The Heat's On Hot Potatoes Grade 7 Sampler

2 HOT POTATOES EXPECTATIONS work cooperatively, respect each other, work safely, and keep a clean work space use the terms heat and cooling capacity and conduction identify and describe heat capacity in liquids and gases relate heat capacity to everyday living MATERIALS water (room temperature) rubbing alcohol (room temperature) thermometers retort stands string plastic wrap elastic bands 500 ml Pyrex beaker test tube beaker tongs WORK SAFELY hot water bath (pan of water on a hot plate, kept at 212 F or 100 C) cold water bath (pan of ice water) safety glasses hot plate oven mitt Hot Potatoes Chart (page 53) graph paper Investigate Explore and compare the heat capacity of liquids and gases and use this information to discuss solids and their ability to hold heat. Fill a Pyrex beaker with water at room temperature. Record the precise amount of water in the beaker. Suspend a thermometer in the beaker (Don t let it touch the glass!) and measure the precise temperature. Record the temperature beside 0 minutes in the water column of chart. Wear safety glasses while you are working over the hot water bath. Place the test tube in the hot water bath (See the Student Background Information sheet.) and record the temperature every minute for 10 minutes. 46 Sci-Tech Connections : The Heat s On / Curriculum Plus 2006

3 Repeat the process with the same volume of rubbing alcohol, and then with air. To trap the air in the beaker, place several layers of plastic wrap over the beaker and fasten with an elastic band. Make a small hole in the plastic wrap and insert the thermometer so that it is suspended in the air, not touching the sides or bottom of the beaker. Make a second chart, identical to the first, and repeat the entire experiment, but this time place the beakers of water, alcohol, and air in an ice water bath. Graph each set of results on a separate graph, placing temperature on the y axis and time on the x axis. THINK AND CONSIDER Will the liquids heat up to the same temperature in the same amount of time? Why or why not? Will all solids heat up at the same speed? Will they all attain the same temperature? Is the same true for gases? Why or why not? Is the opposite true for cooling a liquid? Cooling a gas? How does your investigation relate to the scenario? Continuing the Learning Make generalizations about the heating and cooling capacities of liquids and gases, then use this information to compare solids. THINK AND CONSIDER Compare: walking on pavement with walking on grass in the hot weather a Styrofoam cup with a ceramic cup filled with hot tea. a house made from wood with a house made of bricks. cooking a cake or pie in a tin pie plate or a glass pie plate. Which states heat the quickest? To the highest temperature? If something heats up quickly, does it cool down just as quickly? Sci-Tech Connections : The Heat s On / Curriculum Plus

4 NOTES TO THE TEACHER GET READY Make a supply of ice cubes. Check glassware to make sure that there are no flaws. SAFETY CONSIDERATIONS Safety glasses or goggles should be worn at all times when working over the hot water bath, as the boiling point of alcohol is quite low. In addition, flawed Pyrex may shatter when heated. Make sure that the temperature of the heat source does not exceed 212 F (100 C). Key Understandings compares the heat capacities of different materials describes how high heat capacity materials warm up slowly and cool down slowly describes how low heat capacity materials warm up quickly and cool down quickly recognizes the varying heat capacity of materials and how it affects heating and cooling systems and construction methods INQUIRY AND DESIGN SKILLS exploring, investigating, interpreting, communicating, evaluating, reflecting Introducing the Learning Introduce the illustrated context page. Begin the discussion by asking the following questions. What is a potato made up of? (starch, protein, water) What is popped popcorn made up of? (starch, protein, water, air) How do the popcorn and the potato differ? (The potato has a lot of water, the popcorn mostly air.) If you had 1 lb (500 g) of baked potato chopped up into 1 in (2 cm) cubes, and 1 lb (500 g) of popped popcorn, which do you think would cool down faster? (popcorn) What makes you think this? Do all materials heat at the same rate? How do you know? What do you think heats up the fastest? Give proof. (Students may tell of heating a steel pan and a cast iron pan. The cast iron takes a great deal of time to heat up and a long time to cool down. The other pan heats more quickly but cools as soon as it is removed from the heat.) Introduce the investigation and the materials. Demonstrate using the beaker tongs to handle the hot glassware. Remind students that hot glassware looks exactly like cold glassware. Insure that students set up the experiment so that the thermometers are not touching the sides of the glassware. (Otherwise they will record the temperature of the glass, not the substance inside.) Explain what a hot water bath is. Demonstrate covering the beaker with plastic wrap, securing, and puncturing for the thermometer. 48 Sci-Tech Connections : The Heat s On / Curriculum Plus 2006

5 Have students make predictions about the speed of heating and cooling of the various substances, and test and record these predictions in their notes. When students request more information, introduce the Student Background Information sheet (page 52), or provide a copy of the sheet for each group so that the information can be read and discussed as a team. Interacting with the Learning Which substance heated fastest? Most slowly? Which substance cooled fastest? Most slowly? Did they both retain the same amount of heat? How would you know? Which substance has the highest heat capacity? The lowest? (Refer students to the Student Background Information sheet page 52). How would knowing the heat capacity of a building material help you make decisions when building a house? What heat capacity of construction materials would you want under the following conditions? Give reasons for your answers. cold days, cold nights: (high heat capacity slow to warm initially but good at keeping the heat) warm days, cold nights: (high heat capacity warms slowly during the day, cools slowly at night) warm days, warm nights: (low heat capacity so that any breeze or drop in temperature is quickly reflected in the building s temperature.) Two common methods of heating a house are forced air (The air is heated by a gas or oil flame and then blown into the rooms.) and hot water circulation (radiators). Which of these might be the most appropriate for the following conditions? Give reasons for your answers. (Disregard the possibility of air conditioning.) cold days, cold nights: hot water high heat capacity of water and low heat capacity of air means efficient transfer of heat from water to air; water once heated retains heat warm days, cold nights: forced air, otherwise hot water will continue to heat building during the day; heated air will cool quickly for daytime. warm days, warm nights: forced air for occasional heating, cools quickly. Consolidating the Learning Plan time for students to share their learning by returning to the story and answering the cousins questions regarding heat capacity activities. FOR YOUR INFORMATION The heat capacity of water has implications in the heating and cooling of structures and in their construction. Hot water heat is efficient because the water gives off heat slowly to the air, which has a very low heat capacity and heats up quickly. When the source of the hot water is free, as in geothermally heated water, it becomes very efficient. Brick and concrete, which contain water, heat up slowly and cool slowly, making them ideal construction materials for areas where daytime temperatures are warm and nighttimes cool. Desert dwellers often used adobe, or an adobe-like material, which has a high heat capacity. The adobe would heat up slowly over the day, keeping the interior relatively cool, and then release heat slowly over the cool desert night, keeping the interior warm. Sci-Tech Connections : The Heat s On / Curriculum Plus

6 Think of examples from everyday life when the high heat capacity of water is evident, or times when you take advantage of it. (Outdoor swimming pools still warm in the morning; hot water bottles; hot tubs stay warm for a long time even when turned off; hot water radiators for heating; kettles reboil quickly.) Humid air stays warmer at night than dry air. Explain why. (Humid air contains more water, which has a higher heat capacity, so it retains heat; dry air has low heat capacity, so cools quickly.) East of Detroit, Michigan by 46 miles (74 km) is Point Pelee in Ontario, Canada. Point Pelee is a sand spit about 6 miles (10 km) in length and 1/2 to 1 mile (1 to 2 km) wide that juts out into Lake Erie. It is the southernmost point in mainland Canada. Trees on Point Pelee leaf out significantly later in the spring and retain their leaves later in the fall. Explain why this is so in terms of the heat capacity of the surrounding lake. (Lake cools slowly in the fall due to high heat capacity of water, keeping the point warmer and frost free longer. In the spring, the high heat capacity of water means the lake warms slowly, keeping the temperature on the point cooler and delaying leaf development.) Observing the Learning Does the student follow safety rules? record the necessary information? time the readings accurately? graph the data accurately? interpret the data correctly? use the terms heat and cooling capacity and conduction appropriately? identify and describe heat capacity in liquids and gases? relate the learning from the heat capacity of liquids and gases to solids? apply learning to everyday situations? Strategies for Assessing the Learning 1. Teacher Observation Rating Scale (BLM 24) 2. Mathematics Observation Checklist (BLM 28) 3. Journal Entry Write or draw an analogy for the heat capacity of water. (e.g., Water is like a sponge that can absorb heat.) Connecting the Curriculum SCIENCE/ SCIENCE AND TECHNOLOGY CONNECTIONS Heat causes matter to expand. When we have trouble taking a lid off of a jar, we put the jar lid under hot water. 50 Sci-Tech Connections : The Heat s On / Curriculum Plus 2006

7 Why do we do this? Where else might you use this same technique? Take a deflated balloon (that has been blown up a few times to loosen the balloon) and place it over the mouth of a 2 qt (2 L) plastic soda bottle. Pour hot water over the side of the soda bottle. Predict what will happen, then observe. Explain what happens. What would happen if you put an inflated balloon in the freezer for a period of time? How might what you have observed be used in other ways? Research how the heat capacity of a solid is calculated. MATHEMATICS CONNECTION A calorie is the amount of heat needed to raise the temperature of 1 g of water by 1 C. Calculate the heat energy used to raise the temperature of the water from room temperature to the maximum temperature reached in the investigation, remembering that 1 ml of water = 1 g. HISTORY CONNECTIONS Research building materials and methods used by pre-industrial cultures throughout the world. Analyze the materials and methods with regard to their heat capacities. Research how ancient Roman buildings were heated. LANGUAGE CONNECTION Write a story in which you go back in time to a chosen pre-industrial society (for example, to a medieval castle). In your story, use your 21st century knowledge of heat capacity to help your hosts be warmer in the winter or during cold nights. MATHEMATICS CONCEPT solves and explains multi-step problems HISTORY CONCEPT researches methods of generating heat for daily living in ancient cultures LANGUAGE CONCEPTS communicates ideas and information for a variety of purposes produces pieces of writing using a variety of forms Sci-Tech Connections : The Heat s On / Curriculum Plus

8 STUDENT BACKGROUND INFORMATION Heat capacity refers to the ability of a material to absorb heat energy. In other words, to store that heat energy within the chemical structure of the material. Materials with high heat capacities are slow to heat up. They take a lot of heat energy and store it, without raising their own temperatures very much. Materials with low heat capacities heat quickly: their chemical structures can t store much heat energy, so they give it off again. Materials with high heat capacities also cool down slowly, because they are slow to release the heat energy from their chemical structures, while low heat capacity materials cool quickly. Water has a high heat capacity. It takes a lot of energy to raise the temperature of water, but once it is raised it will stay hot for a long time compared with other substances. Substances that contain a lot of water (like potatoes) will also have a high heat capacity. Hot Water Bath A hot water bath is a controlled method of heating a liquid in a slow and gradual manner. 52 Sci-Tech Connections : The Heat s On / Curriculum Plus 2006

9 HOT POTATOES CHARTS Time (min) Temperature Time (min) Temperature Water Alcohol Air Water Alcohol Air Sci-Tech Connections : The Heat s On / Curriculum Plus

10 PROBLEM SOLUTION Problem List solutions to the problem Choose one solution to consider and place a star beside it. List consequences for the solution Is it a good or bad consequence? How important is the consequence? (Rate 1 to 4) BLM - 16 Sci-Tech Connections BLM 4-8 / Curriculum Plus 2006

11 OBSERVATION RATING SCALE FOR Levels: 4 Independently and goes beyond by challenging self; Thoroughly 3 Independently; Successfully 2 With some assistance; Partially 1 With assistance; Rarely NAMES Does the student Sci-Tech Connections BLM 4-8 / Curriculum Plus 2006 BLM - 24

12 RATING SCALE ASSESSMENT Rating of Name: Date: highly accomplished accomplished acceptable incomplete Shade in the rating scale to show what you think of the model. Provide reasons for given rating below Rating of Name: Date: highly accomplished accomplished acceptable incomplete Shade in the rating scale to show what you think of the presentation. Provide reasons for given rating below BLM - 36 Sci-Tech Connections BLM 4-8 / Curriculum Plus 2006