Materials Included In Kit

Additional Materials Required

Safety Precautions

Make sure students handle the hot metal samples with care. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please consult relevant Safety Data Sheets for additional safety, handling and disposal information before beginning this activity.

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. Collect, dry and store all metal shot samples (Storage code—Inorganic #1). Coffee cup calorimeters can be saved for reuse or disposed of in the solid waste disposal.

Teacher Tips

• This kit is a Super Value Kit. Enough materials are provided in this kit for 5 classes of 30 students working in pairs. Enough shot is provided so half the class can use aluminum shot while the other half is using copper shot.
• This laboratory activity can reasonably be completed in one 50-minute class period. The Prelaboratory Activity should be completed before coming to lab, and the data compilation and calculations can be completed the day after the lab.
• The instructions in the procedure of this laboratory activity have students determine the specific heat of only one of the metals included in this kit. You may wish to have your students determine the specific heat values for both metals instead of just one. To do this, have half the class start with aluminum while the other half starts with copper. Then have them switch metals.
• Different sources use different symbols to represent specific heat, such as s, C_p, C or s.h. This lab uses s to represent specific heat.
• Different masses of water and metal shot may be used. For best results (those that give a temperature change large enough to be easily measurable), choose masses such that the mass of metal is equal to or greater than the mass of water. It is desirable to have a temperature change greater than 10 °C to make sure enough significant figures are present to carry through the calculations.
• Have students take the temperatures of the heated metal shot and water samples immediately before mixing to ensure accurate temperature readings.
• If the test tube holders are not supporting the weight of the tubes and samples, place a piece of masking tape around the upper lip of the test tube to prevent slippage.
• Digital thermometers work well with this experiment and eliminate the risk of breaking a thermometer. Caution students not to leave thermometers standing up in any cup as the cup may tip over and the thermometer may break.
• Clearly identify where students are to return the metal shot samples after they have completed the experiment to avoid mixing the different metals.
• The procedure may be modified to make the lab an open-ended experiment.
  (1) Tell the students the identity of the metal, but do not provide Table 1 (Background section) to them. Have students look up the specific heat for their metal in a chemical reference handbook (CRC) or in their textbook.
  (2) Keep the identity of the metals from the students so that the lab works as an unknown lab. In this case, have students determine the specific heat, then determine the identity of their unknown metal by comparing their value to Table 1.

Answers to Prelab Questions

1. How much energy (in Joules) is needed to heat an iron nail with a mass of 7.0 grams from 25 °C until it becomes red hot at 750 °C?
   q = (m)(s)(ΔT)
   q = (7.0 g) × (0.451 J/g °C) × (725 °C)
   q = 2300 Joules
2. Calculate the amount of energy (in Calories) released during the combustion of a peanut that heats up 100 grams of water from 20 °C to 65 °C. (Note: Food Calories are given in kilocalories where 1 Calorie = 1 kcal = 1000 cal.)
   q = (m)(s)(ΔT)
   q = (100 g) × (1.00 cal/g °C) × (45 °C) × (1 kcal/1000 cal)
   q = 4.5 kcal = 4.5 Calories

Sample Data

Answers to Questions

1. Calculate the
   1. mass of the water by subtracting the mass of the dry calorimeter from the mass of the calorimeter plus water. Record this mass as m_water in the Data Table.
      See Sample Data Table for answers. A sample calculation is given.
      m_water = mass of calorimeter plus water – mass of dry calorimeter
      m_water= 28.04 g – 2.96 g = 25.08 g
   2. temperature change of the water , ΔT_water, by subtracting the initial temperature of the water from the final temperature of the mixture. Record this temperature change in the Data Table. Be sure to include the correct sign with your answer.
      ΔT_water = T_final – T_initial
      ΔT_water  32.2 °C – 20.0 °C = 12.2 °C
   3. temperature change of the metal, ΔT_metal, by subtracting the initial temperature of the metal shot from the final temperature of the mixture. Record this temperature change in the Data Table. Be sure to include the correct sign with your answer.
      ΔT_metal = T_final – T_initial
      ΔT_metal = 32.2 °C – 98.3 °C = –66.1 °C
2. Use Equation 3 to calculate the heat energy gained by the water. Record this value in the Data Table.
   See Sample Data Table for answers. A sample calculation is given.
   q_water = (m_water)(s_water)(ΔT_water)
   q_water = (25.08 g) x (4.184 J/g °C) x (12.2 °C)
   q_water = 1280 Joules
3. Use Equations 4 and 5 to calculate the specific heat of the unknown metal in J/g °C. Record this value in the Data Table.
   See Sample Data Table for answers. A sample calculation is given .
   q_metal = –q_water 
   (m_metal)(s_metal)(ΔT_metal) = –q_water
   (50.19 g) x s_metal x (–66.1 °C) =  –1280 J
   s_metal = 0.386 J/g °C
4. Determine the average specific heat of the unknown metal by averaging the three trials. Record this value in the Data Table.
   See Sample Data Table for answers.
5. Determine the identity of the unknown metal used by comparing the experimental specific heat value to the literature specific heat values listed in Table 1.
   See Sample Data Table for values.
6. Experimental procedures will no doubt lead to some degree of difference from the published literature value. Determine the percent error for specific heat for the metal used. This can be done by comparing the value obtained in the lab (experimental value) with the literature value. Use the equation for percent error below. Record this value in the Data Table.
   {11915_Answers_Equation_11}
   See Sample Data Table for answers. A sample calculation is given below.
   {11915_Answers_Equation_12}

   Percent Error = 0.26% error

7. Compare the experimental and literature specific heat values. How do they compare?
   The values are slightly different because the calculation did not account for any heat lost to the environment or the calorimeter.
8. Suggest possible reasons for discrepancies between the experimental and literature values.
   Heat may have been lost to the environment because the calorimeter did not have a lid and because it is not a perfect insulator. The calorimeter itself also absorbed some energy that was not accounted for. The temperature of the metal was assumed to be equal to the temperature of the boiling water. This may not have been exactly true.

 

Introduction

Experience tells us that if a hot piece of metal is added to water, the temperature of the water will rise. If several different metals having the same mass are heated to the same temperature and added to the same amount of water at the same temperature, will the final temperature of each mixture be the same? Let’s find out with this laboratory activity.

Concepts

• Specific heat
• Heat capacity
• Calorimetry

Background

What Is Specific Heat?

The ability of any material to retain heat energy is called that material’s heat capacity. The measure of heat capacity, or the quantity of heat needed to raise the temperature of one gram of a substance by one degree Celsius, is termed specific heat and is represented by the symbol s. The SI units for specific heat are given in J/g °C. Specific heat values are also commonly given in cal/g °C, where 1 calorie = 4.184 Joules. The specific heats for some common substances are provided in Table 1.

Compare the heat capacities of concrete (0.88 J/g °C) and wood (1.76 J/g °C). Because the specific heat of wood is twice as great as that of concrete, it takes about twice as much heat to raise the temperature of wood than concrete. This can be verified by comparing the feel of walking on concrete versus wood on a hot, sunny day with bare feet. The concrete feels hotter. The sun gives off energy which is absorbed by the concrete and the wood equally. However, because the wood has a greater specific heat value, it is able to absorb more heat before its temperature rises, and therefore it does not feel as hot as the concrete feels to the bare feet.

General Rule 1—The greater the specific heat value, the less the temperature will rise when a given heat energy is absorbed.

Not only does the specific heat value describe how much heat may be absorbed by a substance before its temperature rises, it also describes the ability of a substance to deliver heat to a colder object.

General Rule 2—As the specific heat value decreases, the ability to deliver heat to a colder object increases.

For example, imagine holding two hot pieces of metal—one copper and the other aluminum. If the hot piece of copper was held in one hand and the hot piece of aluminum in the other hand, the hand holding the copper would get hotter. Because copper’s specific heat (0.385 J/g °C) is less than that of aluminum (0.902 J/g °C), the copper sample transfers its heat to a colder object (your hand) more readily.

Why Do Different Materials Possess Different Specific Heat Values?

One reason for the variation is that each substance is made up of atoms that have different masses. The mass of each copper atom is larger than the mass of each aluminum atom, for example. Therefore, a given mass (such as 58 grams) of copper has fewer atoms than the same mass of aluminum. When heat is added to 58 grams of copper, fewer atoms need to be put in motion. Thus, less heat is needed to increase the kinetic energy of the atoms in the sample, and raise the temperature by 1 °C. As a result, the specific heat value for copper is lower than the specific heat of aluminum. Notice that copper and zinc have identical specific heat values. This is due to the similar mass of the atoms.

General Rule 3—The larger the metal atom, the lower its specific heat value.

How Is the Specific Heat of a Material Determined?

Heat transfer or heat flow always occurs in one direction—from a region of higher temperature to a region of lower temperature—until some final equilibrium temperature is reached. In this experiment, heat is transferred from a hot metal sample to a colder water sample. Because each metal has a different specific heat, each metal will cause the temperature of the water to increase to a different extent. The transfer of energy can be detected by measuring the resulting temperature change, ΔT, calculated by taking the final temperature minus the initial temperature, according to Equation 1. For the hotter object in this scenario (the metal), the amount of heat (q) delivered by the metal (q_metal) is equal to the mass of the metal (m_metal) multiplied by the specific heat of the metal (s_metal) multiplied by the temperature change of the metal (ΔT_metal). This relationship is given by Equation 2. For the cooler object in this scenario (the water), the amount of heat absorbed by the water (q_water) is equal to the mass of the water (m_water) multiplied by the specific heat of the water (s_water) multiplied by the temperature change of the water (ΔT_water). This relationship is given by Equation 3. By convention, the sign of q is a signal showing the direction of heat transfer. When heat is transferred out of a material, the sign of q is negative. Conversely, when heat is absorbed by a material, q is positive. The signs of q, along with the necessary associated temperature changes, are summarized in Table 2. According to the Law of Conservation of Energy, the heat delivered by the heated metal, q_metal, must be equal to the heat absorbed by the water, q_water, and its surroundings. Incorporating the sign convention given in Table 2 gives Equations 4 and 5: In this laboratory activity, Equation 5 is used to calculate the specific heat of a heated metal added to a water sample. For calculation purposes, it is important to realize that when the metal is added to the water, the final temperature of both materials will be the same. The calculated specific heat value will then be compared to the known specific heat value given in Table 1.

To make accurate measurements of heat transfer and to prevent heat loss to the surroundings, an insulating device known as a calorimeter is used. A calorimeter is a device used to measure heat flow, where the heat given off by a material is absorbed by the calorimeter and its contents (often water or other material of known heat capacity). In this laboratory activity, a set of two Styrofoam^® cups will be used as the calorimeter.

Sample Calculation

Problem

If a 58-gram sample of metal at 100 °C is placed into a calorimeter containing 60 grams of water at 18 °C, the temperature of the water increases to 22 °C.

1. Calculate the amount of heat absorbed by the water in Joules.
2. Determine the identity of the metal by calculating its specific heat. (Note: Assume no heat loss to the surroundings.)

Solution

a. Use Equation 3.

b. Use Equations 4 and 5.

Using Table 1, the unknown metal can be identified as tin.

Materials

Prelab Questions

1. How much energy (in Joules) is needed to heat an iron nail with a mass of 7.0 grams from 25 °C until it becomes red hot at 750 °C? Show all work.
2. Calculate the amount of energy (in Calories) released during the combustion of a peanut that heats up 100 grams of water from 20 °C to 65 °C. (Note: Food Calories are given in kilocalories where 1 Calorie = 1 kcal = 1000 cal.) Show all work.

Safety Precautions

Handle the hot metal samples with care to avoid burns. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

1. Fill a large beaker about half-full with tap water. Heat the water to a boil using a hot plate or Bunsen burner.
2. Weigh 40–50 g of the assigned metal shot and place it in a large test tube. Record the exact mass of the metal in the Data Table.
3. Put the test tube in the boiling water bath for approximately 10–15 minutes. Be sure the test tube is in the water so the metal is completely submerged.
4. Stack two Styrofoam^® cups, one inside the other. This set of cups will be the calorimeter. Mass the empty calorimeter and record its mass in the Data Table.
5. Pour 25 mL of tap water into the calorimeter and mass the calorimeter again. Record this mass in the Data Table.
6. Measure the temperature of the water in degrees Celsius. Record this temperature in the Data Table.
7. Determine the temperature of the metal sample. To do this, measure the temperature of the boiling water bath. An assumption is made that the temperature of the metal is equal to the temperature of the water bath. Record this as T_metal in the Data Table.
8. Hold the thermometer in the calorimeter with the tap water. Caution: Do not leave the thermometer sitting in the calorimeter because it will likely cause the cup to tip over and break the thermometer.
9. Using a test tube holder, lift the test tube containing the heated metal shot from the boiling water bath and quickly, yet carefully, pour the metal shot into the calorimeter. Make sure no hot water from the outside of the test tube drips into the calorimeter.
10. Gently stir the water and metal shot in the calorimeter with a stirring rod. Measure and record the highest temperature the mixture reaches. Record this temperature in the Data Table as temperature of mixture (T_mixture). Caution: Do not stir the mixture with the thermometer as it could break if hit too hard by the metal shot.
11. Drain the water out of the calorimeter and pour the metal shot onto paper towels. Pat the metal dry thoroughly. Dry the calorimeter. Repeat steps 2–10 for two additional trials using the same type of metal shot.
12. Return the metal shot to the instructor.

Student Worksheet PDF

11915_Student1.pdf