Materials Included In Kit

Additional Materials Required

Safety Precautions

Wear safety glasses when performing this or any lab that uses chemicals, heat or glassware. Care should be taken when handling or placing food onto the pin point. Allow the peanut to cool before touching or discarding it. Use a glass stirring rod to stir the liquid; never stir with a thermometer. Students should not be allowed to eat the peanuts once they are brought into the lab. This lab should be performed in a well-ventilated room.

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. Burned food samples should be allowed to cool and may be disposed of in the trash according to Flinn Suggested Disposal Method #26a.

Teacher Tips

• Enough materials are included in this kit for one group of students. This laboratory activity can be reasonably completed in one 50-minute class period.
• Additional Calorimeter: Introduction to the First Law of Thermodynamics kits (AP4533) may be purchased for each individual lab group.
• Have students practice sliding the cork/peanut assembly into the calorimeter. This must be done quickly after the food has been ignited in order to provide the best results. It should be centered under the flask and remain upright.
• For the best burning results, have students pin the peanut piece at one of the ends so that the piece “points up” and the length is parallel to the pin.
• It may take about 10 seconds to get the peanut ignited, so some heat related to the burning peanut will be lost during this process. The peanut does not have to be completely engulfed in flames before it is placed in the calorimeter. A small flame on the peanut will spread and engulf it over time.
• Be sure that when the food sample burns, it is close but not touching the glass flask. If it is too close to the bottom of the flask, it may extinguish too early due to a lack of oxygen.
• Black carbon soot will deposit on the bottom of the Erlenmeyer flask when the peanut burns. For best results, this soot should be wiped off with a little water and a paper towel between trials. The flask should be cleaned thoroughly after the experiment to prevent the soot from permanently dirtying or staining the glassware.
• Have students try different samples of food in order to compare the caloric contents of different foods. Note: Avoid sugar cookies or other food samples of high sugar content. They tend to get soft as they burn and may fall off the pin. Walnuts, pecans, popped corn, and Cheetos^® (or other puffed snacks) are good choices.
• Different sources use different symbols to represent specific heat, such as s, C_p, C, c or s.h. This lab uses c to represent specific heat.
• Good ventilation is required since burning peanuts can generate a large amount of smoke. Allow some time between trials so that the smoke has time to dissipate.

Sample Data

Data Table

Answers to Questions

1. Heating is required to melt ice or boil water. However, the temperature of the substances remain the same at 0 °C and 100 °C, respectively. Why does the temperature remain the same?

   Where does the heat go? The heat goes into changing the phase of the matter (latent heating). When water reaches 100 °C, it begins to boil because the heating has caused the vapor pressure of the water to be greater than the vapor pressure of the air at sea level. For the liquid phase to turn to gas phase, more heat is required for this change. The heat goes into converting the liquid to the gas, and the heating no longer increases the temperature until all the liquid has changed to a gas. The same occurs when ice melts. Below 0 °C, ice heats up until it reaches zero. Once it reaches the melting point, the heat is used to break the crystal lattice of the ice to form a liquid water. The temperature will not change until all the ice has melted.

2. Why do some foods have more caloric content per unit mass than other foods? Hint: Think about the caloric content of fats, carbohydrates and proteins.

   Carbohydrates and proteins produce the same amount of energy per gram (4 Cal/gram), whereas fats produce more energy per gram (9 Cal/gram). A food that is made with more fat per gram would produce more energy than the same mass of food made mostly with sugar.

3. A “perfect” calorimeter is one that completely reflects all the heat energy so that it does not absorb any heat. This way, all the heat energy will be transferred to the water and the energy given off can be accurately calculated. From your observations from step 13 in the procedure, is this calorimeter perfect? Why or why not? How does this effect the measurement of the heat gained by the water compared to the actual heat released by the burning peanut? List some other possible errors associated with this setup.

   No, this calorimeter is not perfect. The metal tube feels warm meaning the metal tube has absorbed some of the heat given off by the burning peanut. The measured heat gained by the water will be lower than the actual amount of heat released by the burning peanut.
   
   Answers will vary but some possible sources of error include:

   • Heat lost when the peanut was transferred into the calorimeter. Heat gained by the glass of the Erlenmeyer flask and not completely transferred to the water.
   • Food did not burn long enough.
   • Stirring too much will add to an increase in water temperature, and stirring too little will not adequately mix the water and make an accurate temperature reading.
   • Cork began to burn adding more heat to the water than the peanut alone.
   • Assumption that most of the combustion products are gaseous and will not be left on the food sample after it has burned, leaving only unburned peanut on the pin.
   • Not all the heat given off by the peanut was transferred to the Erlenmeyer flask; some was lost to surrounding air and metal container.
4. How much heat is required to increase the temperature of a lake by 2.0 °C that has a total volume of 4.0 trillion (4.0 x 10¹²) liters (approximately 1 cubic mile of water)? Assume the specific heat of the lake water is 1.0 kcal/kg•°C, and the density of the lake water is 1.0 kg/L. On average, how many grams of peanuts would it take to generate this much heat?

   Find the mass of water that is heated:

   4.0 trillion L x 1.0 kg/L = 4.0 trillion kg

   
   Now find the heat required to raise the temperature by 2.0 °C.

   Q = mcΔT
   Q = 4.0 trillion kg x 1.0 kcal/kg•°C x 2.0 °C = 8.0 trillion kcal

   
   Determine the number of peanuts required to generate this much heat.

   Answers may vary depending on student results, but assuming the average peanut generates 2793 calories per grams, it would take:
   8.0 trillion kcal/2.793 kcal/g = 2.9 trillion grams of peanuts burned

References

Kotz, J. C.; Treichel, Jr., Paul. Chemistry and Chemical Reactivity, 3rd Ed.; Saunders College: New York, 1996; pp 264–271.

Tipler, P. A. Physics for Scientists and Engineers, 3rd Ed., Vol. 1; Worth: New York, 1990; pp 518–524, 534–537.

Introduction

Why are some foods considered high calorie? How is the caloric content of food determined? This experiment introduces the concept of calorimetry as well as heat and thermodynamics.

Concepts

• First law of thermodynamics
• Conservation of energy
• Calorimetry

Background

An important concept in the world we live in is that energy cannot be created or destroyed, but only converted between its many different forms (e.g., heat, electrical, chemical, nuclear). This is the law of the Conservation of Energy. This was an important law from which scientists who first studied thermodynamics, or the study of heat energy, temperature, and the transfer of heat energy, used to derive new laws to describe the world. The First Law of Thermodynamics states that the heat energy lost by one body is gained by another body. Heat is the energy that is transferred between objects when there is a difference in temperature. Objects contain heat as a result of the small, rapid motion (e.g., vibrational, rotational, electron spin) that all atoms and molecules (particles) that make up matter experience. The temperature of an object is an indirect measurement of its heat. Particles in a hot object exhibit more rapid motion than particles in a colder object. When a hot and cold object are placed in contact with one another, the faster moving particles in the hot object will begin to bump into the slower moving particles in the colder object and make them move faster (vice versa, the faster particles will then move slower). Eventually, the two objects will reach the same equilibrium temperature—the initially cold object will now be warmer, and the initially hot object will now be cooler. This is the basis for calorimetry, or the measurement of heat transfer.

In the 1770s, Joseph Black was one of the first scientists to conduct calorimetry experiments with different materials and he discovered that not all materials are equal when it comes to heat transfer. He concluded that different materials have their own unique ability to retain heat energy. Some materials, like water, can gain a large amount of heat energy without a significant change in temperature, while other materials, such as metals, will have a more dramatic temperature change for the same amount of heat energy gained. This property is based mainly on the structure of the material, the size of the atoms and molecules, and the interactions between them, and is known as the specific heat of the substance. The specific heat is defined as the heat energy required to raise the temperature of one gram of a substance by one degree Celsius. The unit of energy commonly associated with heat is called a calorie. Water has a defined specific heat of 1 cal/g∙°C so it takes one calorie of energy to raise the temperature of one gram of water by one degree Celsius. (The reverse is also true, remove one calorie of heat from one gram of water, and the temperature will decrease by one degree Celsius.) With the specific heat of a substance known, the amount of heat energy gained or lost by a substance can then be calculated using the following expression:

Q = heat energy
m = mass of the substance
c = specific heat of the substance
ΔT = change in temperature, T_final – T_initial (“Δ” is the Greek letter Delta which means “change in”)

Experiment Overview

In this experiment, the specific heat of water and its change in temperature will be used to determine the caloric content of food. The heat energy that is released is then transferred into the water above it in the calorimeter. The temperature change in the water is then measured and used to calculate the amount of heat energy released from the burning food.

Materials

Safety Precautions

Wear safety glasses when performing this or any lab that uses chemicals, heat or glassware. Care should be taken when handling or placing food onto the pin point. Allow the peanut to cool before touching or discarding it. Use a glass stirring rod to stir the liquid; never stir with a thermometer. Do not eat anything that is brought into the lab.

Procedure

Calorimeter Setup

1. Place the calorimeter tube upright so that the triangle opening is at the base.
   {12807_Preparation_Figure_1_Calorimeter setup}
2. Place the mouth of the Erlenmeyer flask through the hole in the metal calorimeter lid.
3. Slide and snap the plastic Erlenmeyer spill-rim attachment onto the neck of the Erlenmeyer flask such that the metal lid is beneath the rim attachment.
4. Place the flask/lid assembly into the calorimeter tube so that the entire open end of the tube is covered by the metal lid and the flask is centered in the calorimeter.
5. Push the pin through the center of the cork so that the pin head is flush with the cork base.

1. Obtain three whole peanuts and break them into two pieces so that there are six peanut pieces.
2. Determine the initial mass of a peanut piece (one-half of the whole peanut) by measuring with a precision balance. Use peanut pieces that have an approximate mass of 0.3 to 0.5 grams.
3. Obtain a cork/pin assembly, and carefully place the peanut piece onto the pin so that it is centered and secure. Care should be taken to ensure the peanut piece does not break or crack. The pin does not have to stick into the peanut piece very far for it to be secure.
4. Slide the cork/pin/peanut assembly into the calorimeter through the triangle opening, making sure the peanut sample is approximately 1 to 2 cm below the bottom of the flask. Then remove the cork/pin/peanut assembly.
5. Mass the cork/pin/peanut assembly and record this mass in grams in the data table.
6. Measure 50.0 mL of water using a graduated cylinder. Pour the contents into the 125-mL Erlenmeyer flask in the calorimeter.
7. Measure the temperature of the water with a thermometer. Record the temperature in degrees Celsius as the initial water temperature in the data table.
8. Place the cork/pin/peanut assembly near the triangle opening in the calorimeter tube.
9. Ignite the base of the peanut piece with a lighter or match and quickly slide the cork/pin/peanut assembly into the calorimeter and center it beneath the flask. This step must be done quickly so little heat is lost and accurate results are achieved.
10. As the peanut burns, gently stir the water with a stirring rod. Caution: Do NOT stir with the thermometer. Watch to make sure the cork does not begin to burn which would create errors in the results. Do not create wind currents which may prematurely extinguish the flame.
11. Once the peanut sample is completely extinguished continue to stir for 15 to 30 seconds.
12. Measure the maximum temperature that the water reaches. Record this temperature in degrees Celsius as the final water temperature in the data table.
13. Lightly touch the side of the calorimeter tube. Does it feel warm? Use these observations when answering Post-Lab Question 3.
14. Mass the cork/pin/peanut assembly again, and record the final mass in grams in the data table.
15. Repeat steps 2–14 for four more peanut pieces.
16. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

12807_Student1.pdf