We conducted an experiment about heat capacity. Specifically we investigated the calorie content of different foods. Here is a very well written lab report covering the experiment. The"Reference" section needs more detail, however. Please study the report and you will learn both how to write a lab report and you will understand a lot about the energy content of substances.
I. Purpose: To determine the heating value (calorie content) of various substances, especially foods.
II. Materials: 1. Known volume of water in 250 ml Erlenmeyer flask
2. Thermometer
3. Known mass of vegetable oil (approx. 2 grams)
3a Food-stuff or other combustible material (about 2 grams)
4. Watch glass
5. Cotton wick
6. Apparatus stand and flask clamp
III. Procedure: A. Introduction: The word calorimetry comes from the Latin word "Calor" meaning heat, and "-metry" meaning to measure. The method depends on burning a known mass of something as fuel and recording the increase in temperature of a known mass of water. The calorie is a unit of heat energy that is defined at the amount of heat required to raise the temperature of one gram of water (initially at 4 degrees Celsius) by one degree. Thus, ten calories is the amount of heat to raise ten grams of water by one degree, or one gram of water by ten degrees. Starting with water at its freezing point, it would take approximately 100 calories per gram to raise it to its boiling point. To evaporate water at its boiling point takes an additional 540 calories per gram.
B. Method: In this experiment, some students will measure the heat released by burning vegetable oil. Other students will use a small amount of vegetable oil (weighed) as a fuel to start another substance, such as a corn chip, etc., to burn. All materials are carefully weighed and the masses recorded in the student notebooks. In all cases, the results will be expressed as "calories per gram." The heat that is released by the combustion is used to raise the temperature of a known amount of water in a flask. The final temperature of the water in the flask is read and from it is subtracted the initial temperature. This temperature difference multiplied by the mass of the water in the flask represents the amount of heat liberated by the fuel in calories. (In the event the fuel is very energy-rich, or if too much fuel is used, the water in the flask may boil. In this case, the amount of liquid evaporated in grams must be determined (by subtraction from the amount initially present) and that difference must be multiplied by 540 calories to determine the amount of heat released by the fuel to vaporize the water. That amount of heat plus the amount of heat to raise all of the water to the boiling point from the starting temperature is the total heating value of the fuel.
C. Example: 50 ml of water initially at 22 degrees Celsius is heated by burning vegetable oil. The amount of oil initially present was 5 grams. When the experiment was stopped, 1.5 gram of oil remained and 10 ml of water had evaporated. What is the heating value of the oil?
IV. Results: Ans: From the statement of the problem, we know that 10 ml of water, or 10 grams, had been converted to vapor. Since it takes 540 calories per gram to evaporate at the boiling point, we know the amount of heat to evaporate the water was 540 cal/g X 10 g = 5,400 calories. We also know that we started with 50 ml (50 g) of water and this went from 22 degrees to 100 degrees, a difference of 78 degrees. We multiply 50 g X 78 degrees X 1 cal/degree/g = 3,900 calories. We add 3,900 calories + 5,400 calories to get 9,300 calories. The amount of oil that was burned was 5 g - 1.5 g = 3.5 g. Dividing 9,300 calories by 3.5 g yields a heating value of 2,657 calories per gram of oil.
V. Error Analysis: Some heat was lost to the surroundings because the experiment was not conducted inside of a thermally insulated calorimeter. To give support to the oil as it burned, a cotton wick was used. Combustion of the wick may have added a little energy to the water as it heated. Combustion of the oil was not complete. We know this because a layer of soot accumulated on the bottom of the flask. Had the oil burned completely, there would not have been the soot layer and more water would probably have evaporated.
VI. Conclusions: To a first approximation, this experiment allowed us to calculate the heating value, or enthalpy, of oil. Had we used a mix of oil and a food, we could have used the data to determine how much of the heat came from the food and how much came from the oil.
VII. References: Holt Chemistry
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