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An Investigation Into Heat Transfer, Cooling Capacities, and Dilution BY RENEE CLARY 34 H eat energy experiments are fun for students, relatively easy to conduct, use minimal equipment, and can effectively integrate mathematics. Heat transfer can be documented through temperature changes that track energy flow. This article describes inquiry investigations that verify—or contradict— claims that rocks can successfully chill a beverage without diluting it. The science of heat Thermal energy results from the kinetic motion of atoms and molecules: When the particles within an object move faster, the thermal energy of the object increases. Heat is the thermal energy that is transferred between systems of different temperatures. The heat of a system is mass dependent, but temperature can be used to compare how hot or cold an object is, because it is a measure of the average energy of the object. When objects of different temperatures are placed together, heat flows from the warmer object to the cooler one until thermal equilibrium is achieved. The specific heat of a substance is the amount of heat needed for a unit mass of the substance (e.g., 1 g) to increase or decrease in temperature by one degree (e.g., 1°C). Heat is not only required to raise the temperature of an object, but it is also involved in phase changes: A substance requires heat to move from its solid to its liquid phase. Different objects and different phases of the same substance have varying heat capacities. The specific heat capacity of H2O, for example, is 1 cal/g°C in its liquid phase (water) and 0.5 cal/gºC in its solid phase (ice). Because rocks do not undergo phase changes within the normal temperatures and pressures of our daily lives, the phase change of ice cubes into water is critical in this experiment: The energy necessary for the phase change transfers more of the drink’s heat into the ice, which makes the drink much cooler. The law of conservation of energy states that the total amount of energy in isolated systems remains the same. Therefore, we know that when two substances of different temperatures are placed in contact, heat will flow from the warmer substance to the cooler one. When they have reached equilibrium, heat lost is equal to heat gained. Cooling a drink: “On the rocks” versus ice Can rocks be more efficient at cooling a beverage than ice? Advertisements CONTENT AREA Heat transfer, conservation of energy GRADE LEVEL 6–8 BIG IDEA/UNIT Ice is more effective at cooling beverages than rocks (“whiskey stones”) ESSENTIAL PRE-EXISTING KNOWLEDGE Heat flows from warmer to cooler substances, and these changes are documented with temperature changes (heat lost = heat gained) TIME REQUIRED 45 min. COST < $30 (three sets of whiskey stones range from $20 to $30 ) A p r i l / M a y 2 0 17 35 state that “whiskey stones” are the perfect way to cool a drink without diluting it. Like ice, the stones are cooled in a freezer and put into a beverage. Unlike ice, they do not melt at room temperatures, so no phase change is involved. Whiskey stones are made of soapstone, which is primarily talc that has been metamorphosed through pressure and heat. Talc is the softest mineral on the original Mohs hardness scale (Mohs 1, out of 10), but commercial soapstone is typically Mohs 2.5 or harder (Figure 1). These rock cubes are inexpensive, reusable, and nonporous, which decreases the risk of bacterial growth. A set of nine whiskey stones can be purchased for under $10, and only two or three sets will be needed for six to eight lab groups in a classroom of 30 students. on heat transfer, convection, or conduction, simple demonstrations and activities that use the PredictShare-Observe-Explain framework are available. These can help teachers identify students’ alternative conceptions about heat (Brown 2011). A typical Predict-Share-Observe-Explain sequence involves • using students’ prior experiences or knowledge to introduce a challenging question, • introducing the investigation, • recording students’ predictions of what will happen, • discussing students’ predictions, • conducting the investigation and observing the results, Classroom investigation: Ice versus rocks • explaining results, Can soapstone actually cool your drink? In this investigation, students explore whether rocks can chill a liquid as efficiently as ice cubes, with the added benefit of not diluting the drink. Students can design and conduct this experiment as an inquiry activity or follow a general procedural outline for a fun, guided investigation. If your students need a refresher • providing scientific explanations, and • following up if needed (Haysom and Bowen 2010). Give each group of two to four students: • 2 thermometers, PELEX; RA’IKE, VIA WIKIMEDIA COMMONS |FIGURE 1: Talc and soapstone Talc (left) is a soft mineral easily scratched with your fingernail (Mohs hardness = 1) and has multiple commercial uses. Soapstone (right) is primarily metamorphosed talc and can have a hardness greater than 1. Commercial soapstone is typically 2.5 Mohs or more but is always less than 5.5; it can be scratched with a knife. 36 BEAT THE HEAT! AN INVESTIGATION INTO HEAT TRANSFER, COOLING CAPACITIES, AND DILUTION • 2 identical containers (beaker, large foam cup, or small foam cup with aluminum foil on top to hold the thermometer), • a graduated cylinder, • 2–4 soapstone cubes (placed in a freezer overnight; the number of soapstones should approximate the volume of a single ice cube for easy visual comparison; typically, three stones = one ice cube), • water, and • ice (typically one or two ice cubes per group). |FIGURE 2: Recording temperature for ice versus rocks By providing different groups Initial water temperature readings are recorded, then rocks are added to one with different containers—such container, and an ice cube is added to the other. Temperature readings are as glass and foam—the groups’ recorded for each container in two-minute intervals for 30 minutes. results can be compared and used to facilitate discussions termine the mass of the ice cube beabout insulating materials. fore water is added. Alternatively, (Safety note: Students should By providing different they can measure the final volume wear chemical splash goggles groups with different of the water in the container after when conducting the experiment. They should also wear containers—such as glass the ice has completely melted. They and foam—the groups’ should remember that 1 mL of wainsulated gloves when handling results can be compared ter has 1 g of mass.) cold materials.) After noting the initial temperaFor students who may need and used to facilitate ture of the 50 mL of water (room additional scaffolding to dediscussions about temperature at time 0), students then sign and carry out an investiinsulating materials. record the temperature within each gation, you can provide a data container every two minutes, for 30 collection sheet (see Online minutes total. One student in each Supplemental Materials) and group can be the time keeper, one student can be simple instructions. We direct students to meathe data collector for the rock-and-water mixture, sure 50 mL of room temperature water for each and one student can be the data collector for the icecontainer and place a thermometer in each. Next, and-water mixture. (Each data collector can write students record the masses for the soapstones and down the temperature observed in the assigned ice cubes used in the experiment. Soapstone cubes container, or a fourth student in the group can serve are added to one container, and an ice cube is addas the scribe.) ed to the other (Figure 2). (Note: Students can de- A p r i l / M a y 2 0 17 37 | At the conclusion of the exFIGURE 3: Sample graph periment, students graph their data and interpret the graphs. An example of collected data and the resulting graph are shown in Figure 3. Student groups then should evaluate the effectiveness of rock cubes for cooling liquids. Although students typically learn that ice is more effective at cooling a liquid, the melting of ice also results in a diluted liquid when it is used to cool any liquid other than water. In Figure 4, for example, the melting of the ice cube would add enough water to the liquid to increase its volume by 62% (dilution = [original liquid volume] / [final liquid volume]). Students can evaluate whether This graph was produced during an experiment using ~50 ml water, a 30 g ice the cooling capacity of ice offsets cube, and three soapstone cubes within glass beakers. the dilution factor of the original liquid. This can be accomplished age containers of similar compositions (e.g., foam, by asking students to investigate at home whether glass, waxed paper). diluting 50 mL of their favorite beverage with water (using the dilution percentage they calculated in their experiment) will result in a beverage that is still Classroom extensions: Beat the heat appetizing. Students assemble a lab report of their experiIn addition to recording data, determining how ment and results, which teachers can score usdata should be used for analysis, and constructing ing Thomas’s (2010) modified rubric (see Online a graph, students can compare container results, Supplemental Materials). Teachers should provide graph class averages, or for differentiated instruction students with the rubric at the beginning of the with advanced classes, calculate the amount of heat experiment so that they are aware of the required involved in their experiments. report components of the report. In addition to submitting lab reports with the data and analyses, Calculating the heat groups should also present their results and recomUsing the equations below, students can calculate how mendations to the class. If groups used different much heat was removed from the water when it was types of containers (Figure 4), ask students to comcooled with the rock cubes or the ice cube, at the lowpare group results and determine why differences est temperature of the water mixture. For example, exist (Figure 5). Teachers should ask students which students can answer, “What was the total amount of variables changed in this experiment (i.e., containheat dissipated when 50 mL of water was cooled from ers’ composition) and whether they personally 25°C to 22°C using the soapstone rocks?” The amount experienced different chilling effects with beverof heat removed from the system is calculated using 38 BEAT THE HEAT! AN INVESTIGATION INTO HEAT TRANSFER, COOLING CAPACITIES, AND DILUTION heat lost = mcΔT where m is the mass of the water, c is the specific heat capacity, and ΔT is the change in temperature. Therefore, because 50 mL of water has a mass of 50 g, and water has a specific heat capacity of 1 cal/g-°C, |FIGURE 4: Ice versus rocks sample data Different groups can test large foam cups or smaller, coffee-sized cups with aluminum foil over the top to hold the thermometer in place. heat lost, water + rocks = (50 g) × (1 cal/g-°C) × (25°C − 22°C) = 150 cal How does this compare with the heat lost by 50 mL of water in the water-and-ice mixture, to a low temperature of 9°C? (Note: Although the melting ice cube adds water to this system, the calculation is beyond the skill level of most middle school students.) Using the sample data from Figure 4, heat lost, water + ice mixture = (50 g) × (1 cal/g-°C) × (25°C − 9°C) = 816 cal Students can also compare the heat removed in investigations using different containers and mathematically relate the insulating capacities of these containers. Other activities, such as engineering insulated “penguin homes,” can also extend the concept of heat transfer and heat loss to the atmosphere (Schnittka, Bell, and Richards 2010). Additional classroom investigations Other inquiry investigations can be identified, designed, and conducted with student groups. Some potential questions that students may answer include: • What happens if we change the liquid and substitute lemonade or milk? • Will other solid objects—such as gravel pebbles or glass marbles—work as well as the soapstone for cooling a liquid? Other uses for soapstone cubes Teachers can also conduct density investigations using cube volumes determined by both direct measurements and displacements. Teachers can also Water and ice Volume of water added 50 mL Mass of beaker 232 g Mass of beaker and ice 262 g Mass of ice 30 mL Freezer temperature −20°C Water temperature, initial 25°C Volume of water, conclusion 80 mL Water and rocks Volume of water added 50 mL Mass of rocks (3) 60 g Freezer temperature -20°C Water temperature 25°C Volume of water, conclusion 50 mL A p r i l / M a y 2 0 17 39 use the soapstone cubes for mineral investigations (including hardness, or what scratches soapstone and what soapstone scratches; and reactivity to vinegar), and students can create data tables and bar graphs for the various minerals examined. |FIGURE 5: Sample graph using various containers (glass, foam, and foam with foil cover) with 50 mL water and either an ice cube or three soapstone cubes. Discussion In addition to functioning as an inquiry investigation that requires students to collect, analyze, and graph data, the Beat the Heat activity also asks them to evaluate a claim about the effectiveness of rocks in chilling a beverage. Although many students wrote that having an undiluted liquid is a positive attribute, most students still argued against rock cubes for chilling beverages, primarily because they are less efficient than ice. Therefore, this experiment also conveys the message that claims should be investigated, and not taken at face value. Ice and soapstone investigations can be tailored for a range of student skills, including student-driven inquiry or guided experimentation, additional differentiation for extended topics, or more advanced scientific and mathematical concepts. I hope you try the activities in your own classroom, achieve results of improved student understanding of heat transfer, and increase student interest for experimentation. • REFERENCES Brown, P. 2011. Teaching about heat and temperature using an investigative demonstration. Science Scope 35 (4): 31–35. Haysom, J., and M. Bowen. 2010. Predict, observe, explain: Activities enhancing scientific understanding. Arlington, VA: NSTA Press. National Governors Association Center for Best Practices and Council of Chief State School Officers (NGAC and CCSSO). 2010. Common core state standards. Washington, DC: NGAC and CCSSO. NGSS Lead States. 2013. Next Generation Science Standards: For states, by states. Washington, DC: National Academies Press. www.nextgenscience.org/next-generation-sciencestandards. Schnittka, C., R. Bell, and L. Richards. 2010. Tried and True: Save the penguins: Teaching the science of heat transfer through engineering design. Science Scope 34 (3): 82–91. Sumrall, W.J., and D. Rock. 2002. The cycles of math and science. Science Scope 25 (7): 18–22. Thomas, J.D. 2010. Getting students to be successful, independent investigators. Science Scope 33 (6): 24–31. ONLINE SUPPLEMENTAL MATERIALS Data collection sheet and lab report rubric—www.nsta.org/ scope1704 Renee Clary ([email protected]) is associate professor, graduate coordinator, and director of the Dunn-Seiler Museum in the Department of Geosciences at Mississippi State University in Mississippi State, Mississippi. She also serves as director of the EarthScholars Research Group and the 15 Degree Laboratory. 40 BEAT THE HEAT! AN INVESTIGATION INTO HEAT TRANSFER, COOLING CAPACITIES, AND DILUTION Connecting to the Next Generation Science Standards (NGSS Lead States 2013) • The chart below makes one set of connections between the instruction outlined in this article and the NGSS. Other valid connections are likely; however, space restrictions prevent us from listing all possibilities. • The materials, lessons, and activities outlined in the article are just one step toward reaching the performance expectations listed below. Standard MS-PS3-4: Energy www.nextgenscience.org/pe/ms-ps3-4-energy Performance Expectation MS-PS3-4. Plan an investigation to determine the relationships among the energy transferred, the type of matter, the mass, and the change in the average kinetic energy of the participles as measured by the temperature of the sample DIMENSIONS CLASSROOM CONNECTIONS Science and Engineering Practice Using Mathematics and Computational Thinking Students determine the volume of water that results when ice and soapstones are used to cool a drink. Disciplinary Core Ideas PS3.A: Definitions of Energy • Temperature is a measure of the average kinetic energy of particles of matter. Students compare and contrast ice and soapstone as effective cooling agents in heat transfer experiments. PS3.B: Conservation of Energy and Energy Transfer • The amount of energy transfer needed to change the temperature of a matter samples by a given amount depends on the nature of the matter, the size of the sample, and the environment. Crosscutting Concept Cause and Effect Students compare the results of using different containers to cool water Connections to the Common Core State Standards (NGAC and CCSSO 2010) ELA RST.6-8.3. Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks. Math MP.2. Reason abstractly and quantitatively. 6.SP.B.5. Summarize numerical data sets in relation to their context. A p r i l / M a y 2 0 17 41