Burning Calories: How Much Energy is Stored in Different Types of Food?

http://www.sciencebuddies.org/science-fair-projects/project_ideas/FoodSci_p012.shtml#procedure

Materials and Equipment

A project kit containing most of the items needed for this science project is available for puchase from AquaPhoenix Education. Alternatively, you can gather the materials yourself using this shopping list:

• 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.

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.

Questions

• 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?