How Many Calories are Contained in Cheetos?
Junk Food Calorimetry
Purpose:
• To determine the energy content in various foods in calories.
• To compare the measured energy content with the energy
content values given on the junk food packages.
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Concepts:
Calorimetry
Conservation of Energy
First law of thermodynamics
Specific heat
Background:
Many people like to eat junk food: Cheese Puffs, Doritos, potato chips, peanuts. They are
good! Despite their great taste, the junk foods are bad for our health because of their high caloric
content. In today’s experiment, we will use the concept of calorimetry to determine how many
calories are contained in different junk foods we eat everyday.
Here’s the science behind our experiment. The Law of conservation of energy states that
energy cannot be created or destroyed, only converted from one form to another. The First law of
Thermodynamics also states that the heat energy lost by one object is equal to the heat gained by
another object. Calorimetry, or the measurement of heat transfer between different objects, is
based on these two principles.
In the 1770s, a scientist named Joseph Black (1728-1799) conducted the first calorimetry
experiment to determine the amount of energy contained in different materials. He discovered that
not all materials are equal when it comes to heat transfer. Some materials, like water, can gain a
large amount of heat energy without significant changes in the temperature, while others, such as
metals, will have a more dramatic temperature change for the same amount of heat energy
gained. This property is known as the specific heat of the substance, formally defined as the heat
energy required to raise the temperature of 1 gram of a substance by 1 degree Celsius. Water has a
specific heat of 1 calorie/(g °C), which means that it takes 1 calorie of energy to increase the
temperature of 1 gram of water by 1 degree Celsius. We will use the specific heat of water to
determine heat energy released by the burning of junk foods.
In today‘s lab, you will burn different junk food items. As you burn the food, its stored energy is
quickly converted into heat energy, CO2, and water. The heat energy that is released by the food
will then be transferred into the water in the calorimeter. Finally, the temperature change in the
water is then measured and used to calculate the amount of energy released from the burning of
food. At the end, we will also compare our experimentally measured energy content with those
found on the Nutrition Labels to evaluate the accuracy and precision of our experimental
procedure.
Safety:
• We will work with open flames. All students must tie back long hair and tuck away any loose
clothing.
• If you are allergic to any foods that we use in the experiment, please notify me immediately.
• Allow the food sample to cool before touching or discarding it.
• Do NOT eat in the lab area.
• In the case of a fire, notify the teacher immediately.
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Part I. Making Predictions
1. What is the purpose of the experiment?
• Sentence frame: The purpose of the experiment is to… by using …
2. What kind of data should we collect from the experiment? Why do we need each of these
data?
• Sentence frame: We need to collect data on … because …
3. Propose a set-up of the calorimetry experiment.
a. Describe in 2-3 sentences how you will perform the experiment using the set-up.
b. Justify why it is an appropriate set-up.
c. Include the following in your set-up:
i. Foods
ii. The type of calorimeter you will be using (consider different materials)
iii. Thermometer
iv. Means of measuring the mass of food
v. Means of igniting the food
4. On your experiment set-up, indicate with arrows the direction of heat flow between the foods
and the water.
5. Based on your response to #4, determine whether the reaction endothermic or exothermic.
Explain.
• Sentence frame: The reaction is (endothermic / exothermic) because the heat moves
from … to …
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Part II. Data Collection
Materials:
• Your favorite junk food samples
• A 100-mL graduated cylinder
• A thermometer
• An aluminum soda can
• A lighter
• Paper clips
• A Triple beam balance
• Water
Procedure:
1. Bend the paper clip and insert it into the rubber stopper. This is your “Food Holder.”
2. Place a food sample on the food holder. Measure and record the combined mass of the food
holder and sample. Place the food holder on the base of a support stand.
3. Using a graduated cylinder, measure and add 50.0 mL of water to an empty, clean soda can.
4. Place the can on a support stand using a metal ring and a wire gauze. Adjust the height of the
can so that it is about an inch (2.54 cm) above the food holder.
5. Insert a thermometer into the can. Measure and record the initial temperature of the water.
6. Light the food sample and center it under the soda can (it will take about 10 seconds to ignite
the food). Allow the water to be heated until the food sample stops burning. Record the
maximum (final) temperature of the water in the can.
7. Measure and record the final mass of the food holder and sample.
8. Clean the bottom of the can and remove any food residue from the food holder with a wet
paper towel.
9. Repeat steps 1–8 two more times with two different snack food samples.
10. Discard the foods in the trash and wipe down the lab benches with wet paper towels. Cleanups are part of your lab performance grade.
Data Table:
Food Sample
Initial Mass
(food sample
and holder), g
Final Mass (food
sample and
holder), g
Initial
Temperature of
water, °C
Final
Temperature of
water, °C
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Part III. Data Analysis
Perform calculations to complete the table below. Refer to the sample calculations below for help.
Food Sample
Changes in the water
temperature, °C
Energy gained by the
water, calories/g
Changes in the mass
of the food, g
Energy content of the
food sample, calories
Energy content in an
entire bag, Calories
Part IV. Drawing Conclusions
1. Rank the junks foods from the highest caloric content to the lowest caloric content. Support
your ranking with the actual numbers from the data table.
• Sentence frame: The caloric content was the highest in … which contained …
calories…
2. Compare your measured energy content values with those found on the Nutrition Label on
your food. Were the measured values higher or lower than the ones on the Nutrition Label?
What factors account for the difference in the two values?
• Sentence frame: The measured energy content values were (higher / lower) than the
ones on the Nutrition label. The factors that led to this difference was … because …
3. Based on your response to #2, explain how you would improve the results of the experiment.
• Sentence frame: I would improve the results of the experiment by… because...
4. What was your assigned role in the experiment? Explain your contribution to the experiment
and comment on how your group worked together during the experiment.
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