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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
PROCEDURE
- Review all safety precautions associated with the use
of an open flame with your instructor.
- Put on your safety goggles. Use a graduated cylinder to
pure 10 mLs of water into a test tube.
- Secure the tube in a fixed test tube holder.
- Obtain the mass of an unshelled peanut. Record this value.
- Carefully pierce the peanut with a needle.
- Anchor the free end of the needle into a lump of clay,
as seen in the DIAGRAM.
- Measure the temperature of the test tube water in degrees
Celcius. Record this value as the initial temperature.
- With your instructor's approval, light a nearby candle.
Once the candle is burning, use it to set the peanut on
fire.
- 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.
- When the peanut has stopped burning, retake the temperature
of the water. Record this value.
- Pour out the test tube water into a graduated cylinder.
Record this volume.
- Place the burnt peanut on the balance and determine its
end mass.
QUESTIONS
- What was the volume of water that was heated by the burning
peanut?
- What was the initial temperature of the water? What was
the final temperature of the water? How many °C did it rise?
- 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.
- 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?
- 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)
- 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
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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