Materials Included In Kit

Additional Materials Required

Safety Precautions

To avoid burns, use extreme caution when working with heat sources, hot water and handling hot glassware. Keep combustible materials 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.

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. 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. Cooled wax may be placed in the trash according to Flinn Suggested Disposal Method #26a.

Lab Hints

• Enough materials are provided in this kit for 24 students working in groups of two or for 12 groups of students. This investigation can reasonably be completed in two 50-minute class period.
• To avoid burns from steam, heat-resistant gloves are recommended rather than the use of tongs to handle the hot 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 time frame. 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.

Teacher Tips

• The guided-inquiry design and procedure section was developed to subtly lead students through the experimental design process. You may decide to provide less/more information than is included therein. So long as the students are challenged to think critically.
• This laboratory provides a unique opportunity to demonstrate the interdisciplinary nature of science. The ability of the distinct disciplines, chemistry and physics, to inform each other is particularly pronounced in this investigation. In fact, many chemistry classes will incorporate a laboratory activity that covers heat transfer.
• 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).

Further Extensions

Opportunities for Inquiry
Expand this advanced inquiry investigation to include convection and radiation by asking students to design alternative experiments that use those thermal energy transfer processes to melt the wax.

Alignment to Curriculum Framework for AP^® Physics 2 

Enduring Understandings and Essential Knowledge
The energy of a system is conserved. (5B)
5B6: Energy can be transferred by thermal processes involving differences in temperature; the amount of energy transferred in this process of transfer is called heat.

The tendency of isolated systems to move toward states with higher disorder is described by probability. (7B)
7B1: The approach to thermal equilibrium is a probability process.

1. The amount of thermal energy needed to change the temperature of a system of particles depends both on the mass of the system and on the temperature change of the system.
2. The details of the energy transfer depend upon interactions at the molecular level.
3. Since higher momentum particles will be involved in more collisions, energy is most likely to be transferred from higher to lower energy particles. The most likely state after many collisions is that both systems of particles have the same temperature.

Learning Objectives
5B6.1: The student is able to describe models that represent processes by which energy can be transferred between a system and its environment because of differences in temperature: conduction, convection, and radiation.
7B1.1: The student is able to construct an explanation, based on atomic-scale interactions and probability, of how a system approaches thermal equilibrium when energy is transferred to it or from it in a thermal process.

Science Practices
1.2 The student can describe representations and models of natural or man-made phenomena and systems in the domain.
6.2 The student can construct explanations of phenomena based on evidence produced through scientific practices.

Answers to Prelab Questions

1. Which of the following processes entails heat transfer by conduction? Explain.
   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.

   The transfer of heat by conduction requires direct contact between two objects with different temperatures. Of the examples given, two fit that requirement: an egg frying in a pan and a damp, cool washcloth placed on the forehead of a child.

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.

3. The conductometer used in the introductory portion of this experiment has a handle made of wood. Explain why this is the case.

   Wood is a thermal insulator. Therefore, any heat transferred from a Bunsen burner flame to the conductometer’s metal components, which are thermal conductors, will not travel through the wooden handle and potentially burn the person holding the conductometer.

4. When heating something using a ringstand, metal clamp and Bunsen burner, why is it necessary to avoid touching the ringstand?

   Materials made of metal such as ringstands and some clamps conduct heat quickly and efficiently. A flame position under a metal clamp for an extended period of time can transfer heat to the metal clamp and subsequently to the ringstand. It is important to be wary of touching these pieces of equipment because they may cause burns.

Sample Data

Introductory Activity

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.
   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. 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.

Part 2. Copper is the best thermal conductor, followed by steel, aluminum, brass and nickel-alloy steel.

Answers to Questions

Guided-Inquiry Discussion Questions

1. Unlike the conductometer used in the Introductory Activity, the metal strips here do not have wooden handles. Therefore you will not be able to hold the strips while heating. How can boiling water be used to heat the metal strips, in a way that does not require you to hold them and risk burning yourself?

   The metal strips can be placed upright in a hot water bath or beaker of boiling water. The strips can be leaned against the sides of the beaker to keep them upright.

2. Which of the materials that you have been given will likely melt at the boiling temperature of water (100 °C)?

   Of the materials provided, the wax beads are the best choice for a material that will melt at the boiling temperature of water.

3. How can the rate at which the metal strips transfer thermal energy to the material identified in Question 2 be measured, or quantified?

   An experiment with the proper controls must be designed. Using a marker or wax pencil, mark a line across each metal strip 9 cm from one end. Obtain three paraffin wax beads. Press one wax bead onto each metal strip, just above the 9-cm mark (see Figure 2).

   {14010_Answers_Figure_2}

   Lift the metal strip to confirm the wax adheres to the metal. Wearing a heat-resistant glove, grasp the tops of all three metal strips together. 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 3). The wax should be above the water and each metal strip should be angled the same. Record the time it takes for the wax beads to slide down past the 9-cm mark. The entire bead does not need to be below the mark, just the bottom edge.

   {14010_Answers_Figure_3}
4. What drawbacks, or experimental shortcomings, can you identify in your experimental setup or apparatus?

   This particular experimental setup limits the ability to precisely measure conduction because the metal strips and wax are exposed to steam. In other words, the heat transfer and melting observed may not be attributable entirely to conduction. We cannot separate the contributions from the steam to the wax’s melting from the contributions from the conduction process.

5. Carry out your experiment and rank the metals in order of increasing thermal conductivity. Justify your ranking based on your experimental results.

   The wax bead on the copper strip melted in 0:42 minutes; the wax bead on the aluminum strip melted in 1:34 minutes; and the wax bead on the zinc strip melted in 2:03 minutes. Thus, the copper is the best thermal conductor, while aluminum and zinc are 2nd and 3rd, respectively.

6. How do your results compare with those determined using the approach prescribed in the Introductory Activity? Justify your observations. That is, if you got similar results from both experiments explain why (e.g. the limitations of the second apparatus were not significant enough to impact the data).

   As in the Introductory Activity, the copper was determined to be the best thermal conductor.

Review Questions for AP^® Physics 2

1. Describe the process of thermal conduction in metals.

   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 slowermoving 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 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.
   Many metals conduct thermal energy well because they have a large number of mobile electrons. These mobile electrons help with heat conduction because as the metal heats up, the mobile electrons gain kinetic energy and have the ability to travel throughout the metal at a faster rate. The fast-moving electrons “bump” into neighboring slow-moving “cooler” electrons and transfer some of their energy to these slower electrons. The energy transfer continues from regions of high thermal energy to areas of low thermal energy until the metal is in thermal equilibrium.

2. Explain why some metals conduct heat slow and others conduct it fast.

   Some metals conduct heat faster than others due to structural differences. Some metals may have impurities that impede heat transfer, and others may have geometrical arrangements of atoms simply not conducive to efficient thermal energy transfer. Consider a bicyclist trying to get from point A to point B, with two options. The first option is a flat, paved road between the two points that the bicyclist can traverse very quickly. The second path is composed of windy, bumpy, and cracked pavement and impedes the bicyclist’s efficient movement. Similarly, on a microscopic level, the arrangement of atoms in a solid form paths for thermal energy transfer that can promote or impede movement of thermal energy.

3. Describe the process of heat transfer by conduction in the guided-inquiry portion of the experiment, starting with the hot plate and ending with the wax.

   The hot plate has a ceramic top. As it is heated, the atoms that compose the ceramic top vibrate vigorously and thereby transfer thermal energy to the glass beaker. The atoms that compose the glass beaker—boron, oxygen and silicon—begin to absorb energy from the hotplate and move vigorously. The thermal energy manifested as vigorous movement on the atomic scale is then transferred to the water molecules in the beaker. The water molecules begin to move with more random motion and at faster speeds. They then contact the metal strips. The atoms that compose the bottom portions of the metal strips acquire thermal energy, begin to vibrate, and transfer their thermal energy up the strips to the wax. The wax absorbs thermal energy, and the atoms that compose the wax begin to move and ultimately spread apart enough that the wax melts, or undergoes a phase change from solid to liquid.

4. 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 these values? If not, what are some possible sources of error?

   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).

5. 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.

6. In chemistry labs, flammable chemicals, such as acetone and methanol, are commonly stored together in metal cabinets. Tests have shown that the internal temperature of a metal cabinet can rise as much as 1400 °F in a fire, whereas the internal temperature of a wooden cabinet rises only 8 °F. Explain.

   Because wood is a thermal insulator, it does not transfer heat well. Thus, even in a fire, the external wood on the cabinet absorbs heat until it becomes completely charred (and used up as a fuel source) without transferring any heat to the internal portion of the cabinet. In contrast, heat easily moves through metal into the internal contents of the cabinet because metal is a thermal conductor.

References

AP^® Physics 1: Algebra-Based and Physics 2: Algebra-Based Curriculum Framework; The College Board: New York, NY, 2014.

Introduction

A wooden spoon used to stir boiling pasta is safe to hold whereas a metal spoon would burn the chef. This is the case because wood is a thermal insulator and metal is a thermal conductor. That is, the thermal energy (heat) travels easily from the boiling water along the metal spoon until it is too hot to handle. In contrast, thermal energy does not travel readily through wood owing to wood’s microscale structure. In this advanced inquiry investigation, you will quantitatively explore the abilities of various materials to conduct thermal energy, by two methods. The introductory activity will provide detailed instructions for carrying out the first method while the guided-inquiry activity is less structured, requiring you to think through the experimental design process and engage in error analysis.

Concepts

• Thermal conductivity
• Qualitative vs. quantitative processes
• Thermodynamics
• Heat transfer

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 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.

Thermal conductivity is a measure of how well a substance transfers thermal energy (heat) through itself, and to other matter. The higher the thermal conductivity of a substance, the faster heat transfer will take place. Many metals conduct thermal energy well because they have a large number of mobile electrons. These mobile electrons help with heat conduction because as the metal heats up, the mobile electrons gain kinetic energy and have the ability to travel throughout the metal at a faster rate. The fast-moving electrons “bump” into neighboring slow-moving “cooler” electrons and transfer some of their energy to these slower electrons. The energy transfer continues from regions of high thermal energy to areas of low thermal energy until the metal is in thermal equilibrium.

Alloys, or homogeneous metal mixtures, typically have much lower thermal conductivities compared to the pure metals that compose them. Electron mobility and energy transfer are impeded due to the structural differences that result when two or more different atoms mix together to form a homogenous solid. See the Thermal Conductivity of Metals Table on the following page. In this experiment, you will compare the thermal conductivities of several metals to each other and known values, by two methods. The first method is prescriptive and guides you in a step-by-step way through the process. The second method is less structured and requires you to play a more active role in experimental design and error analysis.

Thermoconductivity of Metals

*Approximate values at room temperature (25 ºC). Thermal conductivity is temperature dependent.

Experiment Overview

The purpose of this advanced inquiry investigation is to qualitatively and quantitatively explore thermal conductivity. In the introductory activity, students will press their wrists against plastic and metal samples to come up with a qualitative description of the heat transfer inherent to such contact. In addition, students will measure thermal conductivities of various metals using a special piece of equipment called a conductometer. In the guided-inquiry portion of the investigation, students will devise an alternative method for ranking the thermal conductivities of the metals.

Materials

Prelab Questions

1. Which of the following processes entails heat transfer by conduction? Explain.
   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?
3. The conductometer used in the introductory portion of this experiment has a handle made of wood. Explain why this is the case.
4. When heating something using a ringstand, metal clamp and Bunsen burner, why is it necessary to avoid touching the ringstand?

Safety Precautions

To avoid burns, use extreme caution when working with heat sources, hot water and handling hot glassware. Keep combustible materials 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

Introductory Activity

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.
   1. Which object felt cooler to the touch—the copper strip or the plastic spoon?
   2. What direction was heat flowing—from the objects to your wrist, or from your wrist to the objects? How do you know?
   3. Which object has better thermal conductivity, the plastic spoon or the copper strip? How does this explain the perceived difference in temperature?

Part 2.

1. Obtain a Bunsen burner and, if available, a support stand and clamp.
2. If a support stand and clamp are used, secure the conductometer to the support stand with the clamp. Clamp as close to the wood handle as possible. If a support stand and clamp are not used, carefully hold the conductometer above the Bunsen burner flame positioned as shown in Figure 1.
   {14010_Procedure_Figure_1}
3. Position the dimples on top and the spokes parallel to the tabletop.
4. Obtain five wax pieces (or carefully cut small wax pieces using a razor blade).
5. Press one wax piece (clump) in the dimple at the end of each metal spoke. Brush off any excess wax with a paper towel.
6. Obtain a stopwatch or other timer with a second hand.
7. Light the Bunsen burner and adjust the flame height to approximately 8–10 cm.
8. Position the center hub of the conductometer approximately 10–12 cm over the Bunsen burner flame, making sure the wax pieces are on top and the spokes are parallel to the tabletop. Caution: Hold the conductometer only by the insulated wood handle.
9. As soon as the conductometer is in position, begin timing. Measure the time it takes for the wax to melt completely in each dimple. Record the time measurements in a data table.
10. After 10 minutes, or when all the wax has melted (whichever is first), remove the conductometer from the flame and place it on a heat-resistant ceramic fiber square and allow it to cool for at least 10 minutes. Do not place the hot conductometer directly on the tabletop. It may scorch the finish or cause a fire.
11. Rank the metals in order of increasing thermal conductivity.

Guided Inquiry Design and Procedure
Given the following equipment—aluminum, copper and zinc strips; paraffin wax beads; a marker or wax pencil and other normal labware—design an alternative experiment to the one presented in the Introductory Activity to test and compare the thermal conductivities of the metals. The following instructions and questions will guide you in the experimental design process.

1. Unlike the conductometer used in the Introductory Activity, the metal strips here do not have wooden handles. Therefore you will not be able to hold the strips while heating. How can boiling water be used to heat the metal strips, in a way that does not require you to hold them and risk burning yourself?
2. Which of the materials that you have been given will likely melt at the boiling temperature of water (100 °C)?
3. How can the rate at which the metal strips transfer thermal energy to the material identified in Question 2 be measured, or quantified?
4. What drawbacks, or experimental shortcomings, can you identify in your experimental setup or apparatus?
5. Carry out your experiment and rank the metals in order of increasing thermal conductivity. Justify your ranking based on your experimental results.
6. How do your results compare with those determined using the approach prescribed in the Introductory Activity? Justify your observations. That is, if you got similar results from both experiments explain why (e.g. the limitations of the second apparatus were not significant enough to impact the data).

Student Worksheet PDF

14010_Student1.pdf