Project Kit Available! Order Your Project Supplies

Abstract

Objective

The goal of this experiment is to determine the amount of chemical energy stored in food by burning it and capturing the heat given off in a homemade calorimeter.

Introduction

You know that the energy that keeps your brain and body going comes from the food you eat. Your digestive system and the cells in your body break down the food and gradually oxidize the resulting molecules to release energy that your cells can use and store.

In this project you will learn a method for measuring how much chemical energy is stored in different types of food. You will oxidize the food much more rapidly, by burning it in air. You'll use a homemade calorimeter to capture and measure the heat energy released by burning. The basic idea of a calorimeter is to capture the released heat energy with a reservoir of water, which has a high capacity for absorbing heat. The temperature of the water reservoir is measured at the beginning and at the end of the experiment. The increase in the temperature (in °C) times the mass of the water (in g) will give you the amount of energy captured by the calorimeter, in calories. We can write this in the form of an equation:

• Q_water is the heat captured, in calories (cal);
• m is the mass of the water, in grams (g);
• c is the specific heat capacity of water, which is 1 cal/g°C (1 calorie per gram per degree Celsius); and
• ΔT is the change in temperature (the final temperature of the water minus the initial temperature of the water), in degrees Celsius (°C).

Let's work through an example to make sure that the equation is clear. (We'll use made-up numbers for the example. You'll have to try the experiment for yourself to get actual measurements.) So let's say that we start out with 100 g of water in the calorimeter (m = 100 g). The initial temperature of the water is 20°C. After burning up some small piece of food, we measure the water temperature again, and find that the final temperature is 24°C. Now we have all of the information we need to calculate the amount of heat captured by the calorimeter:

Now you can see why the specific heat capacity of water has such strange units (cal/g°C). Notice that the grams (g) from the mass of the water and the degrees Celsius (°C) from the change in temperature cancel out with the grams (g) and degrees Celsius (°C) in the denominator of the units for specific heat. That way you are left with units of calories (cal), which is what you want.

A calorie (lowercase "c") is actually defined by the heat capacity of water. One calorie is the amount of energy that will raise the temperature of a gram of water by 1°C. When we talk about food energy, we also use the word "Calorie," (note uppercase "C") but it is a different unit. It is the amount of energy needed to raise the temperature of a kilogram (= 1000 grams) of water by 1°C. So a Calorie is the same as 1000 calories. Or, to put it another way, 1 Calorie = 1 kcal. So in this project, for food Calories we will be careful always to use an uppercase "C".

Eating a balanced diet is fundamental to good health. This project will give you a chance to learn about how much energy your cells can extract from different types of food. It is important to remember though, that energy is only one measure of nutritional value. As you are doing your background research on this project, try to find out about other measures of a balanced diet in addition to food energy.

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• calorie (cal),
• kilocalorie (kcal),
• Calorie,
• calorimeter,
• oxidation,
• Recommended Dietary Allowance.

• The reference level for a normal diet is 2000 Calories. How many calories is this?
• What are the basic chemical structures of fats, sugars and proteins?
• Do these types of molecules differ in the amount of energy they contain?
• Which of your food items do you think will release the most energy? Why?
• What is meant by a "balanced" diet? Why is it important?

Bibliography

• Gardner, R., 1999. Science Projects About Kitchen Chemistry. Berkeley Heights, NJ: Enslow Publishers, 40–42.
• The U.S. Department of Agriculture is a good online source of information about nutrition. The links below are for general information, key nutritional recommendations and special pages with information for kids:
  • http://www.choosemyplate.gov/weight-management-calories/calories.html
  • http://www.health.gov/dietaryguidelines/2010.asp

Materials and Equipment

To do this project, you will need the following materials and equipment:

• homemade calorimeter, (for diagram and instructions on assembling, see Experimental Procedure, below) requires:
  • two tin cans, one larger than the other,
  • wood dowel, pencil or other rod-shaped support,
  • cork,
  • needle or wire,
  • hammer and nail,
• graduated cylinder,
• water (preferably distilled),
• thermometer (calibrated in °C, range 20–100 or greater),
• safety glasses,
• lighter or matches,
• scale (calibrated in grams, for determining energy content per gram of food), such as the Fast Weigh MS-500-BLK Digital Pocket Scale, 500 by 0.1 G, available from Amazon.com
• food items to test (dry items will obviously work better), for example:
  • roasted cashew nuts, peanuts or other whole nuts,
  • pieces of popcorn,
  • marshmallows,
  • small pieces of bread,
  • dry pet food.

Order Your Project Supplies

Project Kit Available: $69 Everything you need for this project--- bundled up and delivered to your door! FREE Shipping (Continental U.S. Only) 10% of proceeds go to support Science Buddies!

Experimental Procedure

Figure 1. Diagram of Homemade Calorimeter

1. Constructing the calorimeter (refer to the diagram above).
   1. Select two cans to build your calorimeter. They should nest inside one another. The smaller can needs to sit high enough so that you can place the cork, needle and food item beneath it.
   2. Remove the top and bottom from a coffee (or similar-sized) can, so that you have a cylinder open on both ends.
   3. Use a hammer and nail to make holes in the bottom (to allow air to in to sustain the flame).
   4. Punch holes at opposite sides of the smaller can for the support to pass through. The diagram labels the support as a glass rod, but you can use a wood dowel, a pencil, or a metal rod for the support. Your support needs to be longer than the width of your large can.
   5. Grasp the needle (or wire) and push its blunt end into the cork. You will impale the food to be tested on the sharp end of the needle. (If you use wire, you can wrap it around the food item to be tested. Don't use insulated wire!)
   6. The smaller can will hold the water to be heated by burning the food samples. Use the graduated cylinder to measure how much water you use; the can should be about half-full. Put the supporting rod in place through the two holes.

Figure 2. A top down view of the homemade calorimeter is shown here.

2. Weigh each of the food items to be tested and record the weight.
3. Fill the small can about half-way with a measured amount of distilled water.
4. Measure the initial temperature (T_i) of the water.
5. Impale the food item on the needle (or wrap the wire around it).
6. Have your calorimeter pieces close at hand, and ready for use. For more information on how to properly weigh items see Chemistry Lab Techniques.
7. Place the cork on a non-flammable surface. Light the food item (the nuts may take awhile to catch fire).
8. When the food catches fire, immediately place the large can around the cork, then carefully place the smaller can in place above the flame.
9. Allow the food item to burn itself out.
10. Carefully remove the small can by holding the ends of the supporting rod, and place it on a flat, heat-proof surface. The can will be hot, so be careful.
11. Carefully stir the water and measure the final temperature (T_f). Make sure the thermometer has reached a steady level before recording the value.
12. When the burnt food item has cooled, carefully remove it from the needle (or wire) and weigh the remains.
13. Repeat steps 2–13 for all of the food items. It's a good idea to repeat the measurement with multiple samples of each food item, to insure consistent results.
14. Analyze your data. Calculate the energy released per individual food item (in calories and Calories), and the energy per unit weight of each food item (in calories/gram and Calories/gram). From your individual results, calculate average values for each food type.

• Which food type released the most energy per gram?
• Can you calculate the average energy (in Calories) for each type of food item you tested?
• Do you think the amount of Calories you measured is likely to be higher or lower than the true value for each food item? Why?

Variations

• Do background research to find out the approximate proportions of the different basic food chemicals (fats, carbohydrates, proteins) in each of the food items you tested. Can you draw any conclusions about the relative amounts of energy available in these different types of chemicals?
• Do background research to find out the chemical composition of candle wax (paraffin). Design an experiment to determine the amount of energy released per gram of candlewax.

• For more science project ideas in this area of science, see Cooking & Food Science Project Ideas.

Credits

Andrew Olson, Ph.D., Science Buddies

USC Biology Department, 2004. Burning Calories: The Energy in Food. Biology Department, University of Southern California. Out of print.

Gardner, R., 1999. Science Projects About Kitchen Chemistry. Berkeley Heights, NJ: Enslow Publishers, 40–42.

Last edit date: 2012-02-08 12:00:00