Materials Included In Kit

Additional Materials Required

Prelab Preparation

Station 1: Conduction

Hot Water Bath

1. Fill three 150-mL beakers each with 140 mL of tap water.
2. Place the beakers on a 7" x 7" hot plate.
3. Adjust the temperature setting on the hot plate to maintain a water temperature of 75–80 ºC. Do not allow the water to boil.
4. Place a “HOT” sign in front of the hot plate. (This can be printed using a computer and laminated, or use a “Heat and Burn Hazard” Safety Symbol—Flinn Catalog No. AP6841.)

1. Insert one 2½" piece of glass tubing into one hole of a #5 two-hole rubber stopper from the top. Push the tubing through until about a half centimeter protrudes from the bottom of the stopper (see Figure 8).
   {12623_Preparation_Figure_8}
2. Insert one 5" piece of glass tubing into the other hole of the stopper from the bottom. Push the tubing through until about a half centimeter protrudes from the top of the stopper.
3. Repeat steps 1–2 with two more stoppers and the other pieces of glass tubing.

1. Cut three T-shapes from the laminated template. Save the remainder of the template for additional dividers as needed.
2. Cut the 12" x 18" piece of aluminum foil into six 3" x 12" pieces. Three pieces may be saved for additional dividers.
3. Lay the vertical part of one T in the center of the short side of one 3" x 12" piece of foil, with the edge of the 3" side against the bottom of the cross part of the T (see Figure 9a).
   {12623_Preparation_Figure_9a}
4. Fold each side of the foil in, covering the vertical part of the T (like a gum wrapper). See Figure 9b.
   {12623_Preparation_Figure_9b}
5. Fold the bottom extra length of foil up. Part of the foil will extend beyond the top of the T (see Figure 9c).
   {12623_Preparation_Figure_9c}
6. Fold the tab of foil over the top of the T and press the foil down on the other side (see Figure 9d). Only the two arms of the T should be exposed. The vertical center of the T should be covered in foil. Excess overlapping foil may be trimmed.
   {12623_Preparation_Figure_9d}

1. Clamp each lamp to a support stand or other non-flammable structure, making sure the lamps will stay level.
2. Position the lamps to shine down (see Figure 10).
   {12623_Preparation_Figure_10}

Safety Precautions

Burns are one of the most common laboratory accidents. Review proper safety precautions with your students and teach them how to use the back of their hand to “feel” for heat. To avoid burns, use extreme caution when working with heating equipment, hot water, and handling hot glassware in these activities. Students should wear safety glasses and heat-resistant gloves. Please follow all laboratory safety guidelines. Station 1: Use extreme caution when working with a hot plate and hot glassware. Place a laminated sign reading “HOT” in front of the hot plate. Do not allow the hot water bath to reach the boiling point. Do not place hands directly over the hot water in the beaker. Do not touch the hot metal strips. Allow them to cool on a heat-resistant ceramic fiber square before drying. Station 2: Use caution when working with hot water and hot glassware. Hot tap water can cause burns. Station 3: Use extreme care when working with an open flame. Keep combustible material away from the flame. Do not touch the warm plastic cylinder with bare hands. Use tongs or heat-resistant gloves. Station 4: To avoid burns, use extreme caution while using heating equipment in this activity. Lamps and bulbs get very hot and can cause burns. Do not leave lamps unattended.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Cooled candles, clay, and wax may be placed in the trash according to Flinn Suggested Disposal Method #26a. The materials from each lab should be saved and stored in their original containers for future use. Make sure metal specimens are cool and dry before storing to prevent corrosion.

Lab Hints

Station 1: Conduction

• To avoid burns from steam, heat-resistant gloves are recommended rather than the use of tongs to add or remove the metal strips.
• The wax beads may start to melt but not slip all the way down the metal strips due to friction. As soon as the bottom of a wax bead slips below the mark on a metal strip, students should record the time and remove that strip from the hot water bath, allowing it to cool before the next group starts.
• To avoid crowding around the hot plate, students can be assigned roles—one to watch the time and one to watch the metal strips. If three are in a group, one can record the data.
• Steam from the hot water may be a factor in melting the wax. This variable was taken into account during our testing of the activity. We found that the wax took longer to melt when aluminum foil was placed over the beaker and the metal strips were inserted through narrow slits in the foil, but the order of results was the same.
• A water temperature of 75–80 ºC is ideal to allow the activity to be completed in a 7–10 minute timeframe. Do not allow the water to boil. Periodically check the temperature. Leaving tall thermometers in the beakers is not recommended—the likelihood of a beaker tipping over is too great.

Station 2: Convection of a Liquid

• Any clear, large container may be used to contain the warm water flask, provided the container is tall enough. A 125-mL Erlenmeyer flask will fit inside a 1-L tall form (Berzelius) beaker. A basic 1-L beaker is not tall enough to allow the cold water to cover the glass tubing in the flask.
• To prevent staining of skin, students may want to wear a disposable glove when dispensing the food coloring.
• The greater the difference in temperature of the two regions of water, the more noticeable the convection will be. Hot tap water is usually between 50–60 º C and cold tap water around 18–20 ºC.
• For more efficient use of time, provide large pitchers of ice water to use in the beaker. Students can then obtain the hot water from a faucet with less wait time. Students can pour the cold water directly from the pitchers, eliminating the need for a second 1-L beaker.

Station 3: Convection of a Gas

• Each group should start with a new candle.
• Butane safety lighters rather than matches are recommended for lighting the candles. Student groups may share one lighter without causing much time delay.
• One 250-mL beaker of water is sufficient for all the student groups.
• Be sure the candles are upright and not leaning. The heat from the flame can weaken the wall of the cylinder.
• Leaving the candle burning longer than one minute may cause a weakening and distortion in the wall of the cylinder. Caution students to remove the cylinder after a 30-second burning time. Grasp the cylinder near the top where it is cooler.
• Without the divider, the flame should go out almost immediately after the cylinder is set in place. With the divider, the flame should continue burning. If the cylinder is lowered too slowly over the flame, a convection current may be established without the divider. If the cylinder is lowered too quickly over the flame with the divider, the flame may go out before a convection current can be established. Lowering the cylinder in 2–3 seconds usually works well with and without the divider.
• Replace the aluminum covering for the laminated divider if it gets torn. The aluminum covering protects the laminated divider from being singed or from melting. Replace the divider if damaged.

Station 4: Radiation

• If available, digital thermometers are recommended for faster, more precise measurements.
• If the thermometers appear “top heavy” in the beakers, each can be supported with a clamp attached to a support stand.
• Two graduated cylinders may be shared by all the student groups. Label one “Black Sand” and one “White Sand.”
• Pour each type of sand into separate shallow containers to spread the sand out. This will facilitate cooling between experiments.
• A higher wattage bulb or flood lamp may be used. Be sure the lamp and bulb wattage are compatible before use.

Teacher Tips

• Enough materials are provided in this kit for 24 students working in pairs or for 12 groups of students. Three groups may work at each station at the same time. Students should rotate through the stations every 8–10 minutes. All four stations of this laboratory activity can reasonably be completed in one 45- to 50-minute class period. The prelaboratory assignment should be completed before coming to lab, and the data compilation and calculations may be completed the day after the lab.
• This kit is designed for students to explore the three types of heat transfer—including convection of both liquids and gases. Four hands-on lab stations can be arranged to accommodate three groups of students at each station.
• The day before the lab, prepare copies of the student pages for each student. Encourage students to read through the entire lab before coming to class to facilitate more efficient use of time at each station.
• A good demonstration of the three methods of heat transfer is making popcorn—on the stove (or hot plate) uses conduction, an air popper uses convection, and a microwave uses radiation.
• When students have completed all four stations, use the marshmallow example from the Background section for additional questions such as “Which would be better to use to heat the inside of a marshmallow—a wood stick or a metal skewer?”
• The following kits can be used to further explore heat transfer—Heat Transfer Kit (Flinn Catalog No. AP4536) and Radiation Can Set (Flinn Catalog No. AP5960).

Answers to Prelab Questions

1. Determine whether heat is being transferred primarily by conduction, convection or radiation in each of the following situations.
   1. A bar of chocolate left in the sun begins to melt.

      Radiation

   2. An egg is frying in a pan on a hot electric stove.

      Conduction

   3. Air above a warm beach rises and cooler air from the ocean moves in to replace it.

      Convection

   4. A damp cool washcloth is placed on the forehead of a child with a fever.

      Conduction

2. What precautions should be taken when using heat sources, hot water, and handling hot glassware?

   To avoid burns, use extreme caution while using heat sources, hot water and handling hot glassware. Keep combustible material away from an open flame. Do not leave heat sources unattended. Wear safety glasses and heat-resistant gloves. Follow all laboratory safety guidelines.

Sample Data

Data Table 1

Answers to Questions

1. In Part 1, which object felt cooler to the touch—the copper strip or the plastic spoon?

   The copper strip felt cooler to the touch than the plastic spoon.

2. In Part 1, what direction was heat flowing—from the objects to your wrist or from your wrist to the objects? How do you know?

   Heat was flowing from my wrist to the object. Heat flows from a region of higher temperature to a region of lower temperature. The wrist is warmer than the objects.

3. Which object has better thermal conductivity, the plastic spoon or the copper strip? How does this explain the perceived difference in temperature?

   Metals are better thermal conductors than plastic. Both objects are at room temperature, but the metal feels cooler to the touch because it is conducting heat away from the skin at a faster rate than the plastic.

4. Describe the process of heat transfer by conduction in Part 2, starting with the hot plate and ending with the wax.

   Heat transfers from the hot plate to the beaker, to the water, to the metal strips, and then to the wax.

5. Based on the time required to melt the wax for each metal in Part 2, rank the three metals tested in order of their thermal conductivity, from highest to lowest. Explain your results.

   Copper had the highest conductivity since the wax melted in the least amount of time from the copper strip, followed by aluminum, and finally zinc with the lowest conductivity.

6. Look at the thermal conductivity values for the three metals tested in this activity—the higher the number, the faster heat transfer will take place. Do your results agree with the data in the table? If not, what are some possible sources of error?

   Note: If student data does not agree, possible sources of error include using significantly different sizes of wax beads, pressing some beads flatter than others, a metal strip immersed farther into the water than the others, and wax melting but not sliding down (making it difficult to observe the exact time the wax started to melt).

7. If an iron strip had been tested, when would you expect the wax to melt from the iron compared to the other metals used? Explain your prediction.

   The wax would melt from the iron strip after the other three metals—iron has lower thermal conductivity than aluminum, copper and zinc.

8. Describe any movement of water that was observed once the cold water covered the flask of hot water. Did this movement change over time? If so, how?

   A stream of colored water flowed out of the flask through the longer tube. (Note: Some students may be able to see clear water flowing into the flask through the shorter tube.) The rate of the flow slowed down over time.

9. Did the level of water in the flask or the beaker change? Explain. The water level did not change. As warm water flowed out of the flask, cold water entered the flask through the shorter tube at the same rate.
10. If the flask and beaker setup were left for a longer period of time, would the convection of water eventually stop? Why or why not?

    Convection would eventually stop when thermal equilibrium was reached between the water in the beaker and the water in the flask.

11. Other than convection, what other method of heat transfer was taking place in this activity?

    Heat was transferred by conduction from the water in the flask through the glass to the water in the beaker.

12. In the following diagram, draw arrows to show the convection current in this activity. Label the two regions of water as “hot” and “cold,” respectively.
    {12623_Answers_Figure_12}
13. Describe and compare what happened to the flame in the cylinder without the divider with what happened to the flame with the divider in place. Explain what might have caused the difference.

    The flame got smaller and then went out when the cylinder without the divider was placed over the candle. With the divider in place, the candle continued to burn. Without the divider, the rising warm air (deoxygenated) did not allow cooler (oxygenated) air to flow down into the cylinder. The burning candle quickly used up the oxygen in the cylinder and the flame was extinguished. With the divider in place, the warm air rose up one side of the cylinder and cooler air could flow down the other side, providing oxygen for the candle.

14. Describe your observations when you placed your fingers above the cylinder on opposite sides of the divider.

    One side of the divider felt very warm, the other side felt cooler.

15. What happened to the flame after the divider was removed?

    The flame quickly went out. Note: If the flame does not go out completely, it will flutter and get smaller when the divider is removed.

16. How do the observations from this activity demonstrate that the divider allowed a convectioncurrent to form in the cylinder?

    Student answers will vary—the candle continued to burn, so air was entering from the top of the cylinder on one side of the divider to replace the warm air rising from the candle;some may see smoke rising up one side of the divider, but not the other. Without the divider, the flame went out, so no oxygenated air was entering the cylinder.

17. In the diagram, draw arrows to show the direction of hot and cold air flow in this activity. Show the regions of hot and cold air, respectively, in the diagram.
    {12623_Answers_Figure_13}
18. Calculate the total change in temperature over time by subtracting the final temperature (4 minutes) from the initial temperature (0 minutes). Record the values in Data Table 4.
19. How did the temperature in each substance vary over time? Explain the variation.

    The temperature of the black sand increased nearly 8 ºC which was more than the white sand with an increase in temperature of a little more than 3 °C. The black sand absorbed more radiation from the bulb than the white sand which reflected more radiation.

20. Explain how you can infer that the sand was heated by radiation and not by conduction or convection.

    Conduction requires direct contact to transfer heat—the bulb was not touching the sand. Heat from the bulb transfers to the air around the bulb, causing the warmer air to rise, and the beakers of sand were below the bulb.

21. On a sunny summer day what color shirt—black or white—might be cooler? Why?

    A white shirt would be cooler because it would reflect more heat energy than the black shirt.

Introduction

Have you ever left a metal spoon in a pot on the stove then tried to pick up the spoon with your bare hands? Ouch! Why does the metal spoon get so hot, but a wooden spoon does not? Why does a marshmallow burn when held above a flame, but only gets toasted when it is next to the flame? These questions involve the same principle—transfer of heat.

Concepts

• Conduction
• Convection
• Heat transfer
• Radiation

Background

All matter has heat energy, also called thermal energy. Thermal energy is the energy a substance has due to the continuous motion of the atoms or molecules that make up the substance. Thermal energy always flows from a region of higher temperature to a region of lower temperature. This flow of heat is known as heat transfer. Heat can be transferred in three ways—by conduction, convection and radiation.

Conduction involves the transfer of thermal energy through the direct contact of hot and cold substances. Hotter regions have faster-moving particles (atoms and/or molecules), which collide with and transfer some of their energy to slower moving particles in a neighboring colder region. The faster moving particles will slow down (and this region will cool down) while the slow-moving particles will speed up (and this region will heat up). This energy transfer will continue to proceed down from the “hot” neighbors to the “cold” neighbors, until there is thermal equilibrium, or no temperature difference between the regions. When there is no temperature difference, there is no thermal energy transfer.

Not all materials conduct thermal energy equally. A material’s ability to transfer its heat energy throughout itself, to other substances, or to have heat transferred into it, is known as thermal conductivity. Metals conduct thermal energy much more readily than nonmetals, for many of the same reasons metals conduct electricity better. Materials that do not conduct thermal energy well are known as insulators.

Convection is the movement of fluids of different heat energy from one region to another. Instead of transferring energy directly between particles, a large number of hotter particles (a “hot” region) move and displace a large number of colder particles (a “cold” region) creating thermal convection currents. Convection occurs in liquids or gases in which the hotter regions are less dense and rise, displacing a colder region above. For example, air heats up more quickly at the surface of the Earth than in the upper atmosphere. As the air becomes warmer, it expands, becoming less dense and the air-mass rises. The colder air-mass above will be displaced, sink and then flow in to fill this space. This produces a familiar effect known as wind. As with conduction, when thermal equilibrium is reached, no thermal energy is transferred and convection stops.

Radiation does not require matter to transfer heat—it travels through the vacuum of space. The energy from the Sun that we can see (visible light) is about 43% of the total radiant energy the Sun emits. Most of the thermal energy from the Sun (49%) is in the region of the electromagnetic spectrum called infrared radiation. Infrared radiation cannot be seen by the naked eye, but its effects can be felt as heat. A piece of metal can be heated to a high enough temperature to emit light (such as the tungsten filament of a lightbulb), but even as it cools and no longer glows, it continues to emit infrared radiation. All matter with a temperature above absolute zero emits some infrared radiation.

Experiment Overview

Activity stations are used to demonstrate different methods of heat transfer—by conduction, convection of a liquid, convection of a gas and radiation. Conclusions will be made from observations of each method.

Station 1: Conduction
Some materials conduct heat better than others. In Part 1, compare the thermal conductivity of two materials by using your sense of touch. Metals are generally considered to be good conductors of heat. Do all metals conduct heat at the same rate? In Part 2, compare the thermal conductivity of three different metals.

Station 2: Convection of a Liquid
Investigate the movement of liquids due to differences in temperature.

Station 3: Convection of a Gas
Investigate convection of air as warm air rises from a lighted candle.

Station 4: Radiation
Do some materials absorb radiation better than others? Black sand and white sand will be exposed to the same amount of radiation and the increase in temperature of each will be measured.

Materials

Prelab Questions

1. Determine whether heat is being transferred primarily by conduction, convection or radiation in each of the following situations.
   1. A bar of chocolate left in the sun begins to melt.
   2. An egg is frying in a pan on a hot electric stove.
   3. Air above a warm beach rises and cooler air from the ocean moves in to replace it.
   4. A damp cool washcloth is placed on the forehead of a child with a fever.
2. What precautions should be taken when using heat sources, hot water and handling hot glassware?

Safety Precautions

To avoid burns, use extreme caution when working with heat sources, hot water and handling hot glassware. Keep combustible material away from an open flame. Do not leave heat sources unattended. Wear safety glasses and heat-resistant gloves. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Station 1: Conduction

Part 1

1. Obtain a plastic spoon and a copper metal strip and lay them side-by-side (but not touching each other) on the work surface.
2. Press the inside of your left wrist against the plastic spoon, and at the same time, press the inside of your right wrist against the metal strip.
3. Record your observation under Question 1 on the Conduction, Convection and Radiation Worksheet.

4. Obtain three metal strips—aluminum, copper and the shorter zinc strip.
5. Using a marker or a wax pencil, mark a line across each metal strip 9 cm from one end.
6. Obtain three paraffin wax beads. Press one wax bead onto each metal strip, just above the 9-cm mark (see Figure 1). Lift the metal strip to make sure the wax adheres to the metal.
   {12623_Procedure_Figure_1}
7. Wearing a heat-resistant glove, grasp the tops of all three metal strips together.
8. Without placing your hand directly over the water, carefully lower the metal strips into the hot water bath. Spread the metal strips apart so the wax beads are easily seen on each strip (see Figure 2). The wax should be above the water and each metal strip should be angled the same.
   {12623_Procedure_Figure_2}
9. Start the timer.
10. As soon as one of the wax beads slides past the 9-cm mark, note and record the time in Data Table 1. The entire bead does not need to be below the mark, just the bottom edge.
11. Wearing a heat-resistant glove, remove the metal strip with the melted wax from the hot water bath and place the strip on a heat-resistant ceramic fiber square.
12. Repeat steps 9–10 with the other two metal strips.
13. When cool enough to handle, wipe the metal strips dry with a paper towel.

1. Obtain a 125-mL Erlenmeyer flask. Wearing heat-resistant gloves, fill the flask almost to the top with hot tap water.
2. Add 2 drops of red food coloring to the hot water in the flask. Stir with a stirring rod until the water is a uniform color.
3. Holding the flask with a heat-resistant glove, carefully insert the rubber stopper assembly into the flask. The shorter piece of glass tubing should reach the water.
4. Obtain a 1-L tall-form beaker and slowly lower the Erlenmeyer flask into the beaker.
5. Fill a second 1-L beaker or a water pitcher with about 700 mL of cold water. Fill the tall-form beaker with cold water by carefully pouring the water down the inside wall of the beaker, not over the flask. Fill the beaker with enough cold water to cover the higher glass tube by about ½ centimeter (see Figure 3).
   {12623_Procedure_Figure_3}
6. Start the timer or note the time.
7. Using a thermometer, measure the temperature of the water near the top of the large beaker. Record this temperature as the zero–minutes in Data Table 2.
8. Observe any movement of water or changes in the water level in both the flask and the beaker and record your observations on the worksheet (Questions 8 and 9). (Optional) Place a piece of white paper behind the beaker to better see any movement of liquid.
9. Measure and record the temperature of the water in the beaker every minute for three minutes. Place the thermometer at the same level in the beaker each time.
10. Record any additional observations of the movement of water (Question 8).
11. Remove the flask from the beaker and carefully remove the stopper assembly.
12. Pour the warm water from the flask into the large beaker, and then pour the water from the beaker down the drain.

1. Obtain a large marble-sized piece of clay and a plastic weighing dish. Press the clay into the center of the plastic dish.
2. Obtain a birthday candle. Press the bottom of the candle into the center of the clay so the candle stands up straight (see Figure 4).
   {12623_Procedure_Figure_4}
3. Obtain a butane safety lighter and a 12" plastic cylinder.
4. Check to make sure the cylinder will fit over the candle and piece of clay. If not, reform the clay so it will fit inside the cylinder. Remove the cylinder.
5. Add water to the bottom of the plastic dish, about halfway up the piece of clay.
6. Hold the cylinder in one hand with a heat-resistant glove or tongs.
7. Using a butane safety lighter, light the candle.
8. Quickly lower the cylinder over the candle, standing the cylinder upright in the weighing dish. The water should prevent any air from entering the cylinder from the bottom.
9. Time how long the candle remains lit once the cylinder is in place. Record the time and the appearance of the flame in Data Table 3 on the worksheet. Note: If the candle remains lit more than 20 seconds, it is possible the cylinder was lowered too slowly over the candle. Do not leave the candle burning more than 20 seconds. If this happens, remove the cylinder, blow out the candle, allow the cylinder to cool, and try again.
10. Once the candle goes out, use a heat-resistant glove to grasp the cylinder near the top and remove the cylinder.
11. Obtain a laminated T-shaped divider with the vertical part of the T covered in foil.
12. Insert the vertical part of the T into the top of the cylinder. The T should fit snugly.
13. Repeat steps 6–8 (see Figure 5).
    {12623_Procedure_Figure_5}
14. Allow the candle to burn for 20 seconds. Record your observations of the appearance of the flame. (If the candle goes out before 20 seconds, record the time in Data Table 3.) If the candle continues to burn, record “More than 20 seconds” in Data Table 3.
15. Carefully place one finger from each hand an inch above the cylinder, on opposite sides of the divider for about two seconds. Record your observations (Question 14).
16. Using a heat-resistant glove, remove the T-shaped divider, but leave the cylinder in place. Observe any changes in the flame. Note how much time elapses after the divider is removed until the flame goes out. Record the time and your observations in Data Table 3.
17. If the flame does not go completely out after a total time of 30 seconds, remove the cylinder and blow out the candle.
18. Carefully remove the candle from the clay and place the candle in a beaker of water.
19. Pour out the water from the weighing dish.

1. Using a spoon to scoop the sand from its container, measure 45 mL of black sand into a graduated cylinder. Gently shake or tap the cylinder with a finger to level the sand for a more accurate measurement. Do not tap the cylinder on a hard surface.
2. Pour the sand into a 250-mL beaker. Gently shake or tap the beaker to level the sand.
3. Using a clean graduated cylinder, repeat steps 1–2 with white sand.
4. Place a thermometer in each beaker. Measure the initial temperature of the substance in each beaker. Record the values in Data Table 4 on the worksheet.
5. Place the two beakers on a paper towel close together but not touching (see Figure 6).
   {12623_Procedure_Figure_6}
6. Position a lamp approximately 10 cm over the center of the two beakers (see Figure 7). Turn on the lamp and start the timer or note the time.
   {12623_Procedure_Figure_7}
7. Measure the temperature of each substance in the beakers every minute for four minutes. Record the values in Data Table 4 on the worksheet.
8. Turn off the lamp.
9. Remove the thermometers.
10. Pour the black and white sand back into their respective containers. Stir the sand with a spoon.

Student Worksheet PDF

12623_Student1.pdf