Energy Stored In Food Lab Report

Lab: Energy Stored in Food
Background Questions (5 points each = 10 points):
1. What happens to the molecules of the food that we eat during digestion?
2. What type of metabolism is this?

Background information:
In this lab we will attempt to set a variety of different types of food on fire and capture the heat energy that is given off. The heat energy from the burning comes form the energy stored in the chemical bonds of the food. The more energy in the bonds, the more heat the food will give off. We will capture the heat from the food in the water in a pop can by placing the burning food directly underneath the can. The basic premise of the lab is that the heat from the burning food will raise the temperature of the water in the
can. So our assumption is that the heat gained by the water is exactly equal to heat lost by the food. By knowing the amount of water, the specific heat of water and the temperature change in the water we should be able to calculate the energy gained by the water and this should be the same as the energy released by the food. There are several practical problems with this assumption which will cause your data to differ significantly from the heat values that are printed on the packages of food. During the lab, jot down places where heat may have been lost (that is, not captured by the water), as well as any other problems with the lab that may have given you inaccurate results.

Procedure:
1. Assemble the tin can calorimeter.
2. Measure out 40 ml of water and pour it into the can.
3. Find the mass of the food and record it on the table.
4. Measure the temperature of the water and record it on your table. Remove the thermometer before going on.
5. Place the food on the pin and light it. Quickly, put the burning food under the can. Burn the food to an ash. If the fire sputters and goes out, re-light the food. If you have to keep re-lighting the food, stop, and start again with fresh water and a new piece of food.
6. As soon as the fire is out, measure the temperature of the water and record it on the table.
7. Re-weigh the food and record it on your table.

DATA TABLE 1 (10 points)
Food
Mass before burning
Temp before burning
Mass after burning
Temp after burning ∆ mass
∆t

Calculations:
Remember that we are assuming that the energy gained by the water is exactly equal to the heat stored in the food.
By calculating the heat gained by the water we will figure out the energy stored in the food. Here’s how to calculate the energy gained by the water:

q = cm∆t

Where q is the heat gained by the water c is the specific heat of water (1 cal/g °c) m is the mass of the water in the can and ∆t is the change in temperature of the water

To calculate q, fill in the table below and multiply the values together.
DATA TABLE 2 (10 points)
Food
Specific heat of water
Mass of water in can
∆t of the water
Heat gained by water (cal) Divide by 1000
Kilocalories
(Calories)

1 cal/g °c

1000

1 cal/g °c

1000

1 cal/g °c

1000

1 cal/g °c

1000

1 cal/g °c

1000

1 cal/g °c

1000

1 cal/g °c
1000

The heat gained by the water is measured in small calories (the energy needed to raise the temperature of 1 ml of water 1 degree Celsius).
Food scientists use the large calorie (Cal+ the energy needed to raise 1 liter of water one degree Celsius). To convert cal to Cal, just divide by 1,000.

Our next problem is that the food you burned did not have the same starting mass. That means that big pieces of food would release more energy than some of the smaller pieces of food even if they were really less energetic. To correct for this, we will calculate the energy per gram of each type of food. Fill out the table by dividing the kilocalories by the change in mass to calculate calories per gram:

Kilocalories ÷ ΔM
DATA TABLE 3 (10 points)
Food
Kilocalories
∆ mass
Calories per gram

Finally, you should calculate your percent error by comparing your value for the calories per gram with the experts. Look up at the board and use those calories per gram as the expected values and your calculated calories per gram as the observed value. Plug them into this formula and fill out the table below:

% error = (observed value – expected value) / expected value

DATA TABLE 4 (10 points)
Food
Observed
Expected
%
error

Analysis Questions (10 points each = 20 points):
1. Using the food labels for each type of food you used, identify which organic molecule (carbohydrates, fats or proteins) is in greatest abundance in each food that you burned. For example, by looking at the marshmallow package, it is clear that they are made up mostly of carbohydrates (sugars).
2. List the foods in order from most calories per gram to least.

Conclusion (5 points per paragraph = 20 points):
Paragraph 1: Determine which organic molecule has the most energy, then second most and finally, the least amount of energy stored in its chemical bonds.
Paragraph 2: What are food calories? What do calories in food actually measure? Why do scientists use a measurement of heat energy to measure the energy stored in food?
Paragraph 3: Which types of organic compounds are most associated with energy?
a) Explain why carbohydrates and fats have a lot of calories in them but proteins do not.
b) Draw structural formulas for sugars, lipids, and amino acids and circle all the high-energy bonds.
c) Use these drawings to explain why carbohydrates and lipids are high-energy molecules but proteins are not.
Paragraph 4: Determine all the sources of error in this experiment to explain your percent error you calculated.