Soda Can Calorimeter

Transcription

1 Name Period Soda Can Calorimeter Background The law of conservation of energy states that energy cannot be created or destroyed, only converted from one form to another. This fundamental law was used by scientists to derive new laws in the field of thermodynamics the study of heat energy, temperature, and heat transfer. The First Law of Thermodynamics states that the heat energy lost by one body is gained by another body. Heat is the energy that is transferred between objects when there is a difference in temperature. Objects contain heat as a result of the small, rapid motion (vibrations, rotational motion, electron spin, etc.) that all atoms experience. The temperature of an object is an indirect measurement of its heat. Particles in a hot object exhibit more rapid motion than particles in a colder object. When a hot and cold object are placed in contact with one another, the faster moving particles in the hot object will begin to bump into the slower moving particles in the colder object making them move faster (vice versa, the faster particles will then move slower). Eventually, the two objects will reach the same equilibrium temperature the initially cold object will now be warmer, and the initially hot object will now be cooler. This principle is the basis for calorimetry, or the measurement of heat transfer. An analytical chemist can specialize in different types of chemical analysis. Those who specialize in the analysis of foods perform a variety of tasks that provide information about the nutrient and energy contents of foods. For example, these chemists use calorimeters to determine the calories present in different foods. They run combustion reactions that involve igniting food in the presence of oxygen. These combustion reactions yield carbon dioxide and water as products. They represent the same overall chemical change taking place in your body when it breaks down food to use it as a source of energy. The body uses many more intermediate chemical reactions to produce these products, but the overall change is the same. NOTE: Nutritional Calories (uppercase c) are not the same as calories with a lower case c. Conversion Factors between calories, Calories and joules: 1 calorie (cal) = 4.18 joules (J) 1000 calories (cal) = 1 Calorie (Cal) = 1 kilocalorie (kcal) In this experiment, the specific heat of water and its change in temperature will be used to determine the caloric content of a food sample. The normal unit for measuring the energy content in food is called a Calorie (with an uppercase C). A Calorie is really a kilocalorie, or 1000 calories (lowercase c). During calorimetry, food burns and its stored energy is quickly converted into heat energy and products of combustion (carbon dioxide and water). The heat energy that is released is then transferred into the water above it in the calorimeter. The temperature change in the water is then measured and used to calculate the amount of heat energy released from the burning food. The heat energy is calculated using Q = mcp T.

2 Procedure 1. Place a food sample on the food holder. Measure and record the combined mass of the food holder and sample. 2. Using a graduated cylinder, measure and add 50.0 ml of water to an empty, clean soda can. Record the amount of water you put into the can as grams (1mL = 1 g). 3. Bend the tab on the soda can and slide a stirring stick through the hole. Suspend the can on a support stand using a metal ring. Adjust the height of the can so you can hold the food under it. 4. Insert a thermometer into the can. Measure and record the initial temperature of the water. 5. Light the food sample and center it under the soda can. Allow the water to be heated until the food sample stops burning. Record the maximum (final) temperature of the water in the can. 6. Measure and record the final mass of the food holder and sample. 7. Clean the bottom of the can and remove any food residue from the food holder. 8. Repeat steps 1 7 two more times with two different snack food samples.

3 Pre Lab 1. What is the First Law of Thermodynamic? 2. How are the particles in a hot object different from the particles in a colder object? 3. Explain how the heat gets transfer. 4. Why would it be important to make sure the flame is touching the can? 5. How many calories are in 1 Calorie (nutritional calorie)? 6. How many calories are in 1 Joule? 7. Convert the following values. a. 500 calories = Calories b. 435 calories = Joules c Calories = Joules d Joules = Calories

4 8. Fill out the following table (you will need this for post lab questions): Calorie Content Calorie per serving Serving Size Grams Fuel Value Calories per gram Heat Value Joules per gram Pecans 684 Calories 99 g Tortilla Chips 140 Calories g Corn Chips 160 Calories g 9. The burning of a 0.37 g potato chip cause the temperature of g of water in a soda can calorimeter to increase from 21.5 o C to 28.1 o C. Calculate the amount of heat absorbed by the water. The specific heat of water is 4.18 J/g o C. 10.Convert the above answer to Calories.

5 Data Table Initial Mass & Holder (g) Final Mass & Holder (g) Initial temperature of water ( o C) Final temperature of water ( o C) Mass of Water (g) Pecans Tortilla Chips Corn Chips Post Lab Calculations and Analysis 1. Calculate the change in temperature of water ( T) for each sample. SHOW WORK. T water (Pecans) T water (Tortilla Chips) T water (Corn Chips) 2. Use the heat equation to calculate the heat (Q) absorbed by the water in the calorimeter for each food sample. SHOW WORK. Q for Pecans Q for Tortilla Chips Q for Corn Chips 3. Subtract the final mass of food sample and holder from the initial mass to determine the mass in grams of the food sample that burned in each experiment. SHOW WORK. Mass for Pecans burned Mass for Tortilla Chips burned Mass for Corn Chips burned 4. Use the results from Questions #3 and #4 to calculate the energy content (fuel value) of the food sample in units of Joules per gram (J/g). SHOW WORK. Energy content for Pecans Energy content for Tortilla Chips Energy content for Corn Chips

6 5. Record your results for the energy content of foods along with those of other groups in the class on the board. Pecans (1) Pecans (2) Pecans (3) Tortilla Chips (1) Tortilla Chips (2) Tortilla Chips (3) Corn Chips (1) Corn Chips (2) Corn Chips (3) Mass of Water Temperature Change Heat Absorbed Mass of Burned Energy Content 6. Copy all of the results and use the class data to calculate the average energy content in units of J/g for different types of snack foods. Construct a Class Results Table to summarize the results. Pecans Tortilla Chips Corn Chips Average Energy Content 7. Rank the snack foods in order of their average energy content, from highest to lowest. Which snack food has the highest energy content? The lowest? 8. Compare your average energy content with the ones from the pre-lab. Do you think your results are off on the high side or the low side? Consider the major sources of error in this experiment. Explain how that can affect your results.