Practical - Data logger: Biology
To compare the energy content of different type of food
Time: 2 periods
Apparatus and equipment
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ScienceWorkshop Interface
Temperature Sensor
test tubes
balance
can, small (for calorimeter)
clamp,
food holder
graduated cylinder, 100 mL
stirring rod (2)
Chemicals and Consumables
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cold water
food samples (four different foods: peanut, bread, potato chips, animal fat)
matches
wooden splint
Purpose
To measure the energy value of food in a home-made colorimeter and the data logger.
To compare the energy content of different type of food.
Theory
All human activity requires “burning” food for energy. You will look for patterns in the
amounts of energy released during burning of different foods.
When food burns and heats a known quantity of water, the amount of heat given off by the food
is theoretically equal to the amount of heat gained by the water:
Q  m c  T
where Q is the amount of heat, m is the mass of the water, c is the specific heat of the water,
and T is the change in temperature of the water.
The specific heat of water is:
joule
c = 1 calorie = 4.18
gram C
gram C
Procedure
1.
Measure the initial mass of the food sample.
2.
Put 10 cm3 of distilled water into the test-tube.
3.
Insert a tempterature sensor into the water in the test-tube. Turn on the computer
software to record the temperature change against time.
4.
Use a tongs to hold the first food sample over a bunsen burner until it catches fire.
5.
Transfer the food quickly to the calorimeter.
6.
Stir the water as it is heated up.
7.
Leave the temperature sensor in the water for at least 45 seconds after the food has
stopped burning. Then stir the water until the temperature stops rising.
8.
Click the "STOP" button to end data recording.
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"Run #1" will appear in the Data list in the Experiment Setup window.
9.
Measure the final mass of the remains of the food sample and food holder and record the
mass in the Data section.
10.
Repeat the data recording process for the second food sample. Use a new 50 mL quantity
of cold water.
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After recording data for Sample 2, “Run #2” will appear in the Data list in the Experiment
Setup window.
Result
Energy per unit mass = Q  (m  c  T)/mass of food
Food sample
Initial weight
Final weight
Increase in
temperature
Energy per unit
mass (KJ/g)
Peanut
Bread
Potato chips
Animal fats
Questions
1.
Which food had the highest energy content? What is the major composition of this kind
of food?
2.
Which food had the lowest energy content? What is the major composition of this kind of
food?
3.
Two of the foods in the experiment have a high fat content (peanuts and animal fat) and
two have a high carbohydrate content (bread and potato chips). From your results, what
can you conclude about the relative energy content of fats and carbohydrates?
4.
Suggest the difficulty of measuring the energy value of butter with this set-up?
5.
How can you improve the set up?