Introduction:

Millions of people have been conditioned to count calories in their food and have learned (surprise!) that fatty foods are fattening. Most, however, have little idea what a calorie actually is. It is a unit of energy, just like the joule, the kilowatt-hour, or the foot-pound. The "Calorie" of diet fame is simply the amount of heat energy it would take to raise one kilogram of water one degree Celsius in temperature. In this investigation we will attempt to measure the number of calories released from burning two food items with differing proportions of fats and carbohydrates.

Materials: Empty soft drink can Butane lighter Lab thermometer Dissecting probe Wire screen/stand Aluminum foil or tray Triple-beam balance Forceps or test tube holder Walnut Cracker

Methods:

1) Weigh your food item on the laboratory balance.

2) Fill your soft-drink can about 1/4 to 1/3 full, and weigh it on the balance.

3) Record the initial temperature of the water in the can.

4) Set the can on the stand with the thermometer in it, and place a piece of foil or a small aluminum tray under the stand to catch any falling soot. Carefully impale the food item on the probe, ignite it with the lighter, and then hold it directly under the can until it burns itself out. (Hint: You may need to rotate thefood item to keep it lit, and it will burn more cleanly if the tip of the flame is just below the can.)

5) Record the highest temperature reached by the water.

6) When finished, clean up and return all equipment to its proper place.

Results (Part A): Fill in the following table while doing the lab.

Analysis:

1) Calculate the number of calories in your food using the equation below, and put your answer in the Results Table (Part B). Show your calculations below.

Calories = [(Mass of water in kg) x (Temp change in degrees C) x (1 Calorie)] ÷ (1 kg degree C)

2) Divide total calories of each food item by its mass to obtain Calories per gram.

Results (Part B):

Questions: (Attach a paper with your answers in complete sentences.)

1. Why burn the food? What does this have to do with respiration?

2. Why does a steak turn color from red to brown when cooked?

3. Why did we compute calories per gram instead of just calories?

4. Is there any difference between a "calorie" and a "Calorie"? (Look it up!)

5. Why does this technique usually underestimate the actual number of calories?

6. What is it about the nut that caused it to have more calories?

7. Define "specific heat". Why is the specific heat of water 1?

8. How would the results differ if you kept the food under the lighter flame throughout?

9. If the food is not completely burned, how would this affect your results?

10. What is the practical value of this technique (which is known as calorimetry)?