Download Food energy lab

Food energy lab
Introduction: Every function of your body requires energy, which is supplied by the food you eat. The energy
comes from the breaking of bonds between atoms in the food molecules. The cells in your body have a very
complex method of breaking the bonds to release the energy, but we can break the bonds without eating the
food, also. If the food is burned, the bonds will be broken, and the energy will be given off as heat. It is
possible to determine the amount of energy a food contains by burning a known quantity of it and measuring the
amount of heat given off. In this lab you will determine the energy content in various foods and compare the
differences. Heat released by burning food is measured in units called calories.
1 heat calorie = the amount of heat required to raise the temperature of 1 gram of water by one degree Celsius
1 food calorie = 1000 heat calories (also called a kilocalorie, or Kcal)
Purpose:
To find out how many calories are in a marshmallow, a cashew, and a cheese puff.
Hypothesis: Answer the following questions in your notebook:
Which food do you think will have the most calories? Why?
Which food do you think will have the least calories? Why?
Materials:
ring stand
matches
foods
can
paper clip
balance
glass stirring rod
graduated cylinder
cork
thermometer
Procedure:
1. See the setup provided with the soda can and ring stand.
2. Weigh out the food to be tested and record the mass.
3. Secure the food on the paper clip in the cork. The top of the food should be approximately 1 cm away
from the bottom of the can.
4. Using the graduated cylinder, measure out 50 mL of water and pour it into the can.
5. Precisely measure the temperature of the water and record it in the table.
6. Ignite the food with the matches and allow it to burn until all the food is burned.
7. After the food has completely burned to ash, measure and record the final temperature of the water.
You must do this quickly so the water does not have a chance to cool.
8. Calculate the change in temperature and record it in the table.
9. Repeat steps 2 through 8 with different foods, making sure you change the water in between. Record
the data for each food.
Data Table:
Needs to have space to record all of the following for 3 foods:
 Type of food
 Trial 1, 2, and 3
 Mass of food
 Beginning water temperature
 Ending water temperature
 Change in water temperature
 Heat calories
 Food calories
 Food calories per gram of food
 Average food calories per gram
Calculations:
To find the number of heat calories released by the food, use the formula
H = m x C x T
H is the heat in calories (this is the answer you’re looking for)
m is the mass of water in grams (1 mL of water = 1 gram)
C is the heat capacity of water (1 cal/g•ºC)
T is the change in temperature of the water
Example of how to use the formula:
Say you burned the peanut and the 50 mL of water went from 18ºC to 52ºC. The temperature change is
52-18 or 34ºC. Do the following calculations:
H = m x C x T
H = (50 g) x (1 cal/ g•ºC) x (34ºC)
H = 1700 calories
To convert that to food calories, divide heat calories by 1000.
To find food calories per gram, divide food calories by the mass of food.
Now calculate the average food calories per gram for each food.
Conclusion: Answer the following questions IN CSIQ:
1. Which food had the highest number of calories per gram? Why do you think this food has the most
calories per gram?
2.
Which food had the lowest number of calories per gram…why?
3.
How did your results compare with your hypothesis?
Sources of Error
All foods are a combination of proteins, fats, and carbohydrates. Remember from the “organic molecules notes”
that proteins and carbohydrates have 4 calories per gram, and fats have 9 calories per gram. Since all the foods
you burned are combinations of those three nutrients, all of them should have had between 4 and 9 calories per
gram. But you didn’t get numbers that high, so obviously our experimental technique was off a bit.
When food is tested in a laboratory for its calorie content, it is placed in a device called a calorimeter. The
calorimeter is insulated and is surrounded by water. The food is ignited, and all the heat released by the
burning food is transferred to the water. That’s how they come up with those numbers on the nutrition labels
on the backs of food packages.
With the above information in mind, come up with at least 3 possible sources of error, or reasons why you did
not find between 4 and 9 calories per gram for each food you tested.
Your grade on this lab…
…will consist of the following:
 Your two hypotheses
 Your data table, neat and properly filled out
 All calculations shown
 Answers to the conclusion questions
 Discussion of sources of error