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Teaching Guide
Counting Calories
Counting Calories
The Anti-oxidant effects of Vitamin C
Testing for Simple Sugars
Quiz

Image of peanut



Click here for the PDF version of this guide


 

As you learned in "Doctor Empathy", monitoring the caloric content of the foods you eat can greatly impact weight gain or weight loss. Calories that are counted in our everyday diet are based upon the same units of heat that measure the potential energy stored within chemical bonds. As substances react, chemical bonds are broken and reformed. During this process, energy is released. The amount of released energy is measured in calories and is dependent upon the original energy content of the reactant bonds. Foods that are high in calories have chemical bonds that when rearranged give off large amounts of energy. When a high-energy bond is broken, a large amount of energy is released. If the body can't use all of this energy, it stores the access within the chemical bonds of fat.

Nutritionists usually refer to food in terms of kilocalories (1000 calories). When pamphlets and books refer to food energy in kilocalories they use the word Calorie with an uppercase "C". So one Calorie is equal to 1 kilocalorie which is equal to 1000 calories (lowercase "c").

Note to educators


 

TEACHER CAUTION: Before performing this activity, be sure that no student who will enter the room or be exposed to the smoke has a peanut allergy.

THE PEANUT TEST
To determine the calorie content of a particular food, its stored bond energy must be liberated and measured. This energy is released as heat and is transferred to water. As the water absorbs the heat, its temperature rises. By knowing the mass of burnt food, the volume of water, and the change in the water's temperature, you can determine the calories/gram of the burned food.

NOTE Physical scientists define one calorie as the amount of heat needed to raise the temperature of one gram of water by one Celsius degree.

OBJECTIVE
This activity page will offer

  • an activity to determine relative amounts of calories in a peanut
  • an opportunity to integrate mathematics and science
  • an arena for critical thought on experimental design

MATERIALS

  • Large test tube
  • Test tube holder
  • Ring stand
  • Peanut
  • Graduated cylinder
  • Clay
  • Needle
  • Matches
  • Candle
  • Thermometer
  • Laboratory balance
  • Water (maintained at room temperature)
  • Safety goggles

Image of burning peanut

PROCEDURE

  1. Review all safety precautions associated with the use of an open flame with your instructor.
  2. Put on your safety goggles. Use a graduated cylinder to pure 10 mLs of water into a test tube.
  3. Secure the tube in a fixed test tube holder.
  4. Obtain the mass of an unshelled peanut. Record this value.
  5. Carefully pierce the peanut with a needle.
  6. Anchor the free end of the needle into a lump of clay, as seen in the DIAGRAM.
  7. Measure the temperature of the test tube water in degrees Celcius. Record this value as the initial temperature.
  8. With your instructor's approval, light a nearby candle. Once the candle is burning, use it to set the peanut on fire.
  9. Once the peanut has started burning, position it directly beneath the water filled test tube.
    NOTE: when re-igniting the peanut, slide it away from the test tube in order to prevent the candle's heat from warming the water.
  10. When the peanut has stopped burning, retake the temperature of the water. Record this value.
  11. Pour out the test tube water into a graduated cylinder. Record this volume.
  12. Place the burnt peanut on the balance and determine its end mass.

QUESTIONS

  1. What was the volume of water that was heated by the burning peanut?
  2. What was the initial temperature of the water? What was the final temperature of the water? How many C did it rise?
  3. Use the following equation to determine the heat gained by the water:

    Calories = (mass of water) (change in temperature of water)

    For our approximation, we'll equate mLs and grams, therefore: calories = (volume of water) (change in temperature of water)

    We'll also simplify our calculations by assuming that minimal heat was lost to the surroundings. Therefore, we'll set the heat gained by the water equal to the heat lost by the peanut.

  4. What was the initial mass of the peanut? What was the final mass of the peanut? What was the mass of the peanut that was burned?
  5. To calculate the calories per gram of the peanut, use the following equation:

    calories per gram = (heat gained by water)/(mass lost when peanut burned)

  6. To calculate the number of nutritional Calories per gram simply divide the heat calories from question 5 by 1000.

EXTENSIONS

WATER'S MASS
To simplify our calculations, we set the mass of 1 mL equal to 1 gram. How accurate is such an approximation? To find out, use a laboratory balance to obtain the mass of a beaker. Record this value. Use a graduated cylinder to introduce 100 mL of water to this beaker. Determine its new mass. Subtract the initial mass from the final mass to obtain the mass of 100 mL of water. Divide this value by 100 to obtain the mass of 1 mL. Was the approximation you used in the previous experiment acceptable? Explain.

LOSING HEAT
The experimental design was flawed. All of the energy released by the burning peanut was not absorbed by the water. Where did it go?Can you design a better set-up in which less heat energy is lost? Think about it. Then create a set of blueprints for a laboratory tool that would more efficiently transfer heat from a burning material to a quantity of water.

CHECK IT OUT
Survey the labels of a dozen different types of foods. Find out which foods have the most calories per gram. Pool the class results. From this information, can you uncover any similarities in food content that may account for increased Calories?

WEB CONNECTION

The New Food Label
A useful, interactive

FDA Nutrition Label Nutrition on the Web
A teen-created site on nutrition - includes a chat room

A rich resource on the FDA's food guide pyramid


Answers

The activities in this guide were contributed by Michael DiSpezio, a Massachusetts-based science writer and author of "Critical Thinking Puzzles" and "Awesome Experiments in Light & Sound" (Sterling Publishing Co., NY).

Academic Advisors for this Guide:

Corrine Lowen, Science Department, Wayland Public Schools, Wayland, MA
Suzanne Panico, Science Department, Fenway High School, Boston, MA
Anne E. Jones, Science Department, Wayland Middle School, Wayland, MA

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