The Heat Content of Nuts and Snack Foods

OBJECTIVE: In this experiment, you will burn several types of nuts and snack foods in order to determine their heat content per gram.

MATERIALS
For one team:

• one soda can
• centigram balance
• stirring rod
• ring stand and iron ring
• paper clip
• thermometer, range to 110 degrees C
• 2-3g sample of each type of nut or snack food, such as Cheetos, chips or marshmellows

HAZARDS: The obvious concern is for burns. Also some students may be allergic to the nuts and/or their burning. Check with the students before proceeding. Some nuts may be substituted or omitted. Black soot will form on the bottom of the can which may stain clothing.

PROCEDURE:

After the nut/food burns completely, record the final temperature of the water, and determine the actual mass of nut/food that has burned. Repeat the procedure, using a different type of nut/food sample.

RESULTS:
Using your data for the mass of the water, the mass of the nut that actually burned, and the initial and final temperatures of the water, calculate the heat released per gram of nut/food burned.

DISPOSAL: Discard the ash in the waste basket. Recycle the soda cans.

CALCULATIONS: SHOW ALL WORK USED!!!

1. Calculate the change in temperature of the water.
   
   
2. Calculate the heat that was released by the food and absorbed by the water in calories and in joules. (NOTE: 1 calorie(c) = 4.18 J)
   Heat absorbed by water= (mass of water)(temperature change)(1calorie/J€oC)
   
   
3. Calculate the joules released per gram of nut/food that burned.
   
   
4. Examine the "Nutritional Value Information" found on the package of one of the food samples. Note that 1 Food Calorie(C) is equivalent to 4.184 kJ of heat energy. Use this information to determine the "accepted value" for the heat content per gram of snack food. What is the percent error for your experiment?
   
   
5. Explain how can you improve the accuracy of this experiment?
   
   
6. Compare the heat content of the various types of food tested. Use the nutritional information on the side of their packages to determine how much fat and carbohydrates each type of food has. Is there any correlation between these two values?
   
   

DISCUSSION
The value for kilojoules per gram of nut/food determined by this procedure is generally much lower than the value in the literature, but they are proportionately lower for each type of nut/food tested. Students can be challenged to make a more efficient calorimeter. The operation of a bomb calorimeter can also be explained as a closed system where the food is literally "blown up" and all the heat energy is accounted for. The literature value for the heat content of raw almonds is 28.4 kJ/g, Brazil nuts = 30.1 kJ/g, pecans = 31.6 kJ/g, pistachios = 27.6 kJ/g, black walnuts = 28.6 kJ/g and peanuts = 23.6 kJ/g.

REFERENCE: John Grossman, "How Many Calories Are There In A 230-Calorie Dinner?", Hippocrates, Sept/Oct 1987 (5).

Submitted by Justin Field Chemistry Institute 1988 with modifications by Mark Case, CHEM 6 Team Binder 1995.