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Determining the Calorie Content of Foods
You and your partner will test three different food groups to determine the heat released per gram of food burned. The burning of food is a combustion reaction. Different types of food (simple sugars, carbohydrates, and fats) have different chemical compositions and should vary in terms of the amount of energy released during the reaction.
 
Materials
Food (choose three, one from each group)
CBL with temperature probe
Marshmallows
Test tube
Cereal (cheerios, etc.)
Test tube clamp
Peanuts
Aluminum foil
Almonds
Cork
Gummy bears
Straight pin
Croutons
Triple beam balance
Other foods brought from home (chips, cheetos, etc.)
         
This experiment employs a technique called calorimetry. The heat energy from the combustion of the food will be transferred to a measured quantity of water. By measuring the temperature change of the water, you will be able to determine how much energy was released per gram of food burned. It is well documented that in order to make the temperature of one gram of water rise by 1 Co, one calorie of heat must be absorbed. This quantity of energy is called a calorie. You will determine how many calories of heat are given off per gram of food reacted.
 
Before beginning the experiment, you are expected to develop a hypothesis based on what you have learned in this unit. Using your knowledge of the types and number of bonds found in sugars, fats, and carbohydrates, make a prediction as to which food group has the highest and lowest calorie content. You may refer to food labels or conduct an internet search. The hypothesis is an educated guess, and you must be able to justify it with background information.
 
Be sure to clearly state your results in the conclusion. Was the hypothesis valid? What could be done to improve the experiment?
 
In the discussion, list five things you learned about chemical reactions as a result of this investigation.
 
You and your partner will submit a typed lab report. The attached rubric indicates how the lab report will be scored. The report is worth 100 points.
 
Time line: Two class periods will be devoted to the collection of data. Two class periods will be allowed for the analysis of data and preparation of a report.
 
 
Calorimetry
 
Procedure:
 
Carefully weigh the food source to be tested to the nearest tenth of a gram on the scales provided.
 
Cover a cork with a piece of aluminum foil and force a pin that is provided up through the cork to where approximately 2 cm of the pin is protruding from the cork. Mount a test tube on a ring stand and hold into place with a clamp. Allow enough room under the test tube to allow the cork with pin and the food source to be tested.
 
Fill the test tube with 20 mL of water (which is equivalent to 20 g).  Insert the temperature probe without touching the sides or bottom of the test tube and get the beginning temperature in degrees Celsius. Attach the food source to the pin and set fire to the food source. As soon as the food source is burning, place it under the test tube.  Insert a thermometer into the test tube making sure that it does not touch the sides or the bottom. Hold the thermometer in place while the food source is burning. When the temperature reaches a maximum, record that value.
 
 
 
Sample Data:
 
Mass of food source = 1.35 g
Initial temperature of water = 27.0 oC
Final temperature of water = 94.0 oC
Change in temperature = 67.0 oC
 
Sample Calculation:
 
  1. Find the amount of heat absorbed by the water.
 
 
  1. Compare the amount of heat absorbed to the amount of food combusted.
 
 
 
 
Discussion:
 
  1. Consider the food groups - fats, carbohydrates, and sugars. What is similar about the composition of the food molecules? What is different?

  1. Generalize about the energy providing ability of each food group. Which group has the greatest amount of energy stored in the bonds?

  2. Give examples of types of food from each category.

  3. What is a calorie? How does a food calorie differ from a scientific calorie?

  4. What type of reaction is used in calorimetry? What are the products of the reactions? Where did the products go?



E Saylor

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