Learning Library

# Energy Content of Food

• What is a calorie? How does it differ from a Calorie?
• What is a calorimeter?
• Why is it important to determine the caloric values of different foods?
• How is the energy in food released by the human body?
• How many calories should a normal individual, age 16, consume in one day?
• Why are we currently confronted with an obesity problem?
• What measures might the government take to stem the obesity problem/
• What foods tend to be very high in calories?
• What kinds of foods tend to be low in calories?
• What part does or should exercise play in this scenario?

In this day and age we are all concerned with calories. A calorie is a unit used to measure heat. One calorie is the amount of heat needed to raise the temperature of 1g of water 1 degree C. The term calorie comes from the word caloric. In the 1700s, scientists thought that heat was an invisible substance and they named it caloric. Today we know better.

A device called the calorimeter was invented to measure the amount of heat given off when a substance is burned. We still use a calorimeter. In this project, the student will construct a simple calorimeter to capture the energy released by the burning of food. Basically we all require energy in order to live. We obtain this energy from food. If we to trace the food back, it takes us to photosynthesis, a process by which green plants capture the sun`s energy, transforming it into chemical energy that is stored in the chemical structures of molecules. We eat the food.We oxidize and digest the food and in the process release and recover the stored energy. Thus, indirectly, we are using the sun`s energy.

In this project the student will learn how to measure how much energy is stored in different types of food. What will be measured is the amount of heat released in the process of burning different foods. Your calorimeter has a reservoir of water. When the heat of the burning food is released it serves to heat the water in the reservoir in the calorimeter. You will measure the temperature of the water before and after the burning of specific foods.

The increase in the temperature (Degrees C) times the mass of water in grams will tell us the amount of energy we obtained in the calorimeter in calorie units. We use the formula Q of water =mc times change in temperature. Note: Q of water is the heat captured in calories, m is the mass of water in grams, c is the specific heat capacity of water namely 1cal/g per degree Celsius and ^T is theamount of change in temperature in degrees C.

• 2aluminum or metal soda cans (one small, one large)
• Water,
• Matches,
• Large paper clip ,
• Balance ,
• Calculator ,
• Pen,
• Food samples (such as small squares of bread, cheese, banana ,tomato, and lettuce)

These materials may be borrowed from the school science lab and the rest purchased from the local super market.

1. Gather all the materials you will need for the experiment. These include2aluminum or metal soda cans, ,a thermometer (centigrade), a large graduated cylinder, water, matches, a large paper clip , a balance , a calculator , pen, food samples such as small squares of bread, cheese, banana ,tomato, and lettuce.
2. Put on your safety equipment.
3. Copy the data chart provided below so that you may readily record your data.
4. Cut out opening on both sides of the small soda can. Leave the top and bottom intact.
5. Make sure that the smaller can will fit into the larger can and can sit in a stable position.
6. Take your large paper clip and bend it so that the top part is open and can serve to pierce into the pieces of food and that the bottom is able to sit again in a stable position.
7. Use your graduated cylinder, measure off 100ml of water and pour it into the uncut soda can.
8. Place the thermometer into the water and measure the temperature and record in your data chart.
9. Now for each of the pieces of food you will use, measure the mass using your balance and record the data in the data chart.
10. Now you will repeat the following procedure for each of the pieces of food and record your observations in the data chart. Measure the mass of each piece of food and record the data. Start by placing the piece of bread on the clip, pierce it on the clip and place the clip and the bread into the cut can. Now carefully, very carefully place the whole can containing the water on top of the cut can. Now light the bread with the match and let it burn. When it is finished burning, take the temperature of the water in the top can. And then measure the remaining mass.Record your data. Repeat this with all of the food samples, measure the temperature of the water each time, measure the remaining mass and record the data. Yes, use fresh water each time!
11. Using the data you have obtained, apply the formula, Q of water = mc change in temperature for each of the foods and determine the caloric value of each of the foods.
12. Record the data in your chart.

Data Chart

 Sample Foods Initial Mass Final Mass Initial Water Temperature Final water temperature Calories bread cheese banana tomato lettuce

Terms/Concepts: calorie; Calorie; Calorimeter; Fats; Carbohydrates; Proteins; Oxidation; Respiration; Photosynthesis

• Masterton,w,Slowinski,E., Walford, E.,Chemistry, Holt, Rinehart and Winston, New York, 1980

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