Chemistry Thermodynamics Neatly answer all questions completely for credit. Show all work.

Size: px

Start display at page:

Download "Chemistry Thermodynamics Neatly answer all questions completely for credit. Show all work."

Meagan Spencer
5 years ago
Views:

1 Teacher Notes Time: 90 minutes (plus 30 minutes for teacher preparation) Student Difficult: moderate Purpose: Design and model processes, materials, and equipment that might be used to build a device that measures the calories of heat energy available in foods. Overview: Process Skills: Analyzing data Experimenting Applying concepts Identifying patterns Calculating Inferring Collecting data Interpreting Communicating Organizing data Lab Preparation: Prior to the lab, you will need to collect and organize the materials students will need to build a calorimeter. Other readily available materials may be included or substituted for those in the materials list. Notes on Technique Review with students the use of a balance to measure the mass of each sample. Also review the correct method of reading the water level in a graduated cylinder. Immediately after igniting the food sample, students should place the large can around the cork and then quickly but carefully put the small can in place above the flame. If the food flame goes out, the sample should be removed along with its holder, from the calorimeter, reignited, and the apparatus quickly reassembled. If possible, the food samples should be burned until only ashes remain. Reaction Energy 1 Thermochemistry

2 Tips and Tricks This lab works best with groups of 3 4 students. Once the calorimeter is built and before any samples are burned, you might want to have students rehearse the assembly process. The faster they are able to get the burning food sample under the can of water, the more accurate their results will be; less heat will be lost to the surroundings. Igniting the nut samples may take longer than the other foods. Some foods may be more difficult to hold in place than others. In these cases, use a small binder or alligator clips (with a little tube to attach to wire) to hold food. Modeling clay can be a good alternative to cork. Checkpoints 1) By the end of the first class period, have students turn in a detailed one-page plan/procedure for approval. 2) During the second class period, have students revise procedures according to your comments and begin the procedure. 3) After the first data collection, have students turn in a copy of their data so that you can ensure they are collecting data correctly. 4) Following completion of the experiment, have students turn in their procedure, data, and Analysis and Conclusions answers. Students labs should be evaluated on lab technique, quality and clarity of observations, and the explanation of observations and conclusions. Sample Procedure (Procedures will vary). A calorimeter was made from two metal cans, one smaller so it could nest inside the larger can. The top and bottom of the larger can were removed and holes were made in the rim near the bottom to allow oxygen needed for combustion enter. Two small holes were punched in opposite sides of the smaller can about ¼ of the way from the top. A wooden dowel was passed through the holes to support the smaller can above the burning food sample. Using the cork, needle, and pliers, a setup for mounting the food sample for burning was devised. A measured amount of water was added to the smaller can. Both the volume and temperature of the water were recorded. A food sample was massed on the balance and them mounted on the needle. The sample was ignited, and as soon as it caught fire, the large can was placed over the cork and the smaller can with its support was positioned above the flame. When the sample was completely burned, the smaller can was carefully removed. The water was stirred and the temperature of the water was observed and recorded. The burnt food sample was allowed to cool, carefully removed from the needle, and massed. Its mass was recorded. Three trials were made with samples of the same food to ensure consistency. Then the procedure was repeated for three other food samples. Reaction Energy 2 Thermochemistry

3 Background Background information is provided for students. If time allows, interested students can do online research to find out about calorimeter designs. Answers: Analysis 1. Answers will depend on the food choices. 2. Students should find that foods containing fats and oils have higher calorie content. 3. Answers will vary according to the food choices. Students should find that foods with high fat and oil content burned more quickly. 4. Answers will vary. Conclusions 1. Students should find that their heat transfer measurements were higher for foods that are rated as higher in calories. 2. Students should recognize that some heat energy is lost to the air. Students may suggest that a calorimeter design with better insulation would produce more accurate measurements. Students may suggest that a water jacket surrounding the burning sample would collect more of the heat transfer. 3. Students should recognize the relationship between measurements of high calories by the calorimeter and more energy available to the human body. 4. Students should find that their higher measurements were comparable to higher calorie ratings of foods. They should account for the differences by identifying inefficiencies in the calorimeter design. For high-fat foods that don t burn (oddly, some popular snack chips do not burn) students should suggest reasons why. Reaction Energy 3 Thermochemistry

4 Thermodynamics In this lab, you will design, construct, and test your own device to determine the amount of heat energy in snack foods. Purpose: Design and model processes, materials, and equipment that might be used to build a device that measures the calories of heat energy available in foods. Engineering Design Process Identify a Need Conduct Research Brainstorm Solutions Select a Solution Design a Solution What s the problem? What have others done? What are the constraints? How can you solve the problem? Brainstorm multiple ideas. Which ideas best meet the need? Which ideas meet all your constraints? Choose the best one. Describe or draw a diagram of the steps you will take to solve the problem. Make a list of what you will need to implement your solution. Follow your plan. Test and Evaluate Test it out! Analyze your results. Were they what you expected? Think about what your results say about your plan. Redesign to Improve Communicate What changes could you make that would give you better results? Make your design even better. Test it out! Share your results with others throughout the design process and get their feedback. Report on your final design. Prior Knowledge Temperature, Thermochemistry, Heat capacity, Energy transfer, Specific heat, Chemical reaction, Calorimetry Reaction Energy 4 Thermochemistry

5 Possible materials may include, but are not limited to: alligator clips balance can opener cork distilled water gloves, heat resistant graduated cylinder graph paper hammer knife matches metal cans (1 large, 1 small) metal file modeling clay nail needle pencil pliers porcelain tile, large and flat stirrer thermometer tongs wire wood dowel snack foods (a variety, such as, cracker, marshmallow, popcorn, pretzel, potato chip, roasted peanut, cashew or other whole nut) Background Have you ever heard the question, Do you eat to live or live to eat? For most people, the answer is both! Food contains energy that the human body uses to function and survive. That energy, released in the form of heat as food is digested, is transferred to all parts of the body. The unit used for measuring the transfer of heat is the calorie. One calorie (cal) is the energy required to raise the temperature of 1 gram (or 1 ml) of water 1 degree Celsius. The energy content of food is also measured in calories. However, these calories are actually large Calories, or kilocalories (Kcal). A kilocalorie is equivalent to 1,000 calories, or 1,000 times the heat energy of 1 calorie. The number of calories in a particular quantity of a packaged food is often listed on the packaging. Our bodies crave fats because fats come packed with energy. When your body takes in food, it burns that food in much the same way a log burns in a fireplace. So, the more calories your body takes in, the more time it will take for it to burn them off. Think of a big and a small log. Which one will take longer to burn? The calorimeter measures the amount of energy in foods by burning them in the most isolated conditions. This ensures that the maximum amount of heat gets transferred from the burning food so to determine how much energy there is in it. Reaction Energy 5 Thermochemistry

6 Safety Chemistry Thermodynamics While doing this activity, observe the following safety precautions. Always wear safety goggles and a lab apron to protect your eyes and clothing. If you get a piece of burning food on your skin, flush the affected area in a sink immediately, and alert your teacher. Avoid touching sharp edges of metal apparatus. When handling metal apparatus, be careful and conscious of your movements, and avoid cutting your fingers on any unfinished edges. Call your teacher in the event of an accident. Working with open flames is dangerous, and you should take every precaution not to allow burning matches or food near anything flammable. Always work on a nonflammable surface. Procedure 1) Form a hypothesis about what materials or methods you can use to build a device and measure the heat energy of various snack foods. 2) Come up with a plan. Develop and conduct an experiment to determine what methods and materials can be used to measure the heat transfer between food samples and water. Limit the number of trials and foods you choose for your experiment to those that can be completed during the time your teacher has allotted for this lab. Consult with your teacher to make sure that the conditions you have chosen are appropriate. 3) Write out a procedure for your experiment. As you plan the procedure, make the following decisions: a. Decide what methods and/or materials you will use to build your device. b. Decide how you will measure the heat energy transfer. c. Select the materials and technology that you will need for your experiment from those that your teacher has provided. d. Decide the kind of data you will collect and develop a method for recording the data. e. Decide how you will determine that your measurements are as valid as you can make them. f. Decide what safety procedures are necessary. 4) Have your teacher approve your plans. 5) Obtain your materials and set up any apparatus you will need. 6) Take appropriate safety precautions. 7) Make objective observations. 8) Collect data and organize them into appropriate tables and/or graphs. Be certain that the graphs and tables are properly constructed and labeled. Compare the amounts of calories in different foods and identify which foods contain the most energy. 9) Share your results with other teams. Elicit their feedback on your design. 10) Improve your design and test it. Reaction Energy 6 Thermochemistry

7 Name: Class: Date: Chemistry Thermodynamics Cleanup and Disposal Clean all apparatus and your lab station. Return equipment to its proper place. Dispose of foods and ashes in the containers designated by your teacher. Wash your hands thoroughly after all work is finished and before you leave the lab. Analysis 1) Summarizing Data Summarize your findings and observations, including an analysis of any data tables or graphs that you created. 2) Identifying Relationships For each food you tested, describe the heat energy content in relation to other foods. Why do different foods produce different results? 3) Analyzing Methods Did the foods require the same time to burn and did that affect the amount of heat transferred? Did all of the foods burn completely? Reaction Energy 7 Thermochemistry

8 Name: Class: Date: Chemistry Thermodynamics 4) Describing Events Share your results with your classmates. Were your results similar to those of your classmates? Conclusions 1) Drawing Conclusions What conclusions can you draw about the data you collected? What additional conclusions can you draw from class results? 2) Evaluating Models Was your device an accurate device for measuring the calories in food? Was any heat lost? Suggest ways that you could improve the design. Reaction Energy 8 Thermochemistry

Name: Class: Date: Chemistry Thermodynamics 3) Compare and Contrast How does the burning of food in this experiment compare to the use of food by the body?

9 Name: Class: Date: Chemistry Thermodynamics 3) Compare and Contrast How does the burning of food in this experiment compare to the use of food by the body? 4) Evaluate Results How do your results compare to the calorie ratings listed on the packages of the food you tested? What could have influenced any differences? Reaction Energy 9 Thermochemistry

Food as Fuel. Investigative Lab 78. Name Class Date. Measuring the Chemical Energy Stored in Food

Food as Fuel. Investigative Lab 78. Name Class Date. Measuring the Chemical Energy Stored in Food Name Class Date Food as Fuel Measuring the Chemical Energy Stored in Food Investigative Lab 78 Question How can you measure the calorie content of a peanut? Lab Overview In this investigation, you will