Burn Baby Burn: The Power Within! Feedstock Calorimetry. (by Mary C. Criss & Shannon Ralph)

Transcription

1 Burn Baby Burn: The Power Within! Feedstock Calorimetry (by Mary C. Criss & Shannon Ralph) Objective The purpose of this experiment is to determine the amount of chemical energy stored in different biofuel feedstock by using a homemade calorimeter. Introduction In this experiment you will measure the amount of chemical energy stored within various biofuel feedstock. To do this you will need to burn the feedstock in air, capture and measure the heat energy that is released with a reservoir of water. Water is an excellent reservoir because it has a high capacity for absorbing heat, 4.18 J/g C. At the beginning and end of the experiment the initial and final water reservoir temperature is measured in C. To figure the amount of energy captured in calories by the calorimeter, you will need to take the increase in temperature ( C) times the mass of the water in grams. Use the equation given in the data analysis section below. To calculate the energy content of different substances, you will be building your own simplified calorimeter out of an aluminum can. A calorimeter is defined as an apparatus that measures the evolution of heat. You will burn several substances and use temperature changes of water in your can calorimeter to determine the energy released by the combustion reactions. You will compare your experimentally determined values with the calculated values and use your analysis of different calorimeter designs to help you understand and explain possible sources of error in your experiment. (Burning Food and Fuel) Calorimetry is a technique that is used to determine the heat involved in a chemical reaction. When determining the heat of combustion of a substance, the measurements are often made using a bomb calorimeter (Diagram #9). In this device, the weighed sample is placed in a heavy steel container called a bomb and the atmosphere inside the bomb is filled with pure oxygen. The bomb is then placed in a well-insulated container called a calorimeter which has been filled with a measured amount of water. The sample, in the pure oxygen atmosphere, is ignited by an electric spark and the heat generated by the burning sample warms the bomb and the surrounding water. At equilibrium, both the bomb and the water will be at the same temperature. Since energy can neither be created nor destroyed, the heat released by the combustion reaction can be determined by measuring the change in temperature of the water and the bomb. (Burning Food and Fuel) Terms and Concepts Calorie (cal) Calorimeter Biofuel feedstock Chemical Energy Specific Heat Experimental value Theoretical value Energy Joule Percent Error Microalgae Macroalgae Combustion Temperature Bomb Calorimeter 1

2 Materials & Equipment To create the homemade calorimeter (see pictures): o One, 49.5oz Campbell s Tomato Soup tin can, emptied & cleaned with hot soapy water. o One, 7.5 fl oz can of pop (used to hold the water) o Sharpie Marker o 1 roll of Thick Aluminum Foil. o 1 bendable paper clip o One, #10 Cork o Velcro sticky tabs o Metal Tape or duct tape o Pipe wrap insulation (not fiberglass) o Hand operated can opener o Old style (triangle tip) steel can opener o Metal hanger (to bend into a handle for the pop can) o Wire cutters o Scissors To test the homemade calorimeter: o Different feedstock seeds to test (ex., corn, soy bean, peanut, safflower seed, sunflower seed, filamentous algae pellet, dried microalgae flake, rice barley, etc o Cheetos Cheese puffs o Electronic Scale (accurate to 0.00g) o 100 ml Graduated Cylinder o Distilled water o Digital Kitchen Thermometer ( F & C) o Candle Lighter, Adjustable Flame Safety Precautions: You will be dealing with fire so be careful to NOT burn yourself or others at your lab station. The metal stand holding the sample will get hot during the reaction. Handle it using tongs or forceps. HEALTH HAZARD: This procedure involves burning nuts. If you are allergic to nuts, or have any severe food allergies, inform your instructor immediately so that you may be excused from this experiment. Do not stay in the laboratory.. There are no safety hazards with any of the materials used in this experiment. Do not eat any of the foods used in this experiment. It is assumed that they may be contaminated with laboratory chemicals. Modified from 2

3 PROCEDURE: 1. Make your feedstock holder with a cork, paper clip and a Velcro sticky button. See diagram #1. 2. Make an aluminum foil thimble that will hold your feedstock sample. The thimble should be used for feed stocks that will not stick on the end of the paper clip, such as small seeds, etc See diagram #2. Use thick aluminum foil and wrap a small piece around your finger to make a small thimble to hold your feedstock sample to be burned. The thimble will sit on top of the paperclip platform in diagram #1. The thimble apparatus will be placed at the bottom center of the burning chamber. See diagram #3. Use the end of the paperclip to skewer the bottom of the Cheetos. 3. Record the initial mass of the feedstock holder (aluminum thimble or paperclip & cork) and the feedstock item in data table #1. 4. Make your water container with a 7.5fl. Oz aluminum pop can, and ~ 24 cm of wire hanger. See diagram #4. Clean the pop can thoroughly and remove the pop tab. Use wire cutters to cut the wire hanger into 2, ~24 cm sections and straighten the wire. Mark the level locations of the 4 holes using a ruler. You will use the end of the hanger to puncture the holes through the top of the pop can. DO NOT put any duct tape on or in this can. See diagram #4. Bend down the wire hanger ~ 5 cm on each side to hang over the larger, outer can. See diagram #5. 5. Make a lid for the water container by using 2-4 layers of aluminum foil folded and fitted tightly over the can opening & cut off excess aluminum foil. Use the thermometer to gently poke a hole through the lid to fit into the can. Hold the thermometer so that it does not touch the bottom of the can. See diagram #5. 6. Your feedstock holder should be about 2.5cm from the bottom of the water container (pop can). 7. Determine the mass of the empty can and record that in data table #2. 8. Pour 50mL of room temperature distilled water in the can. 9. You will weigh the water can after it has been heated and use the heated weight of the can as your final weight & record the information in data table # Make your burning chamber (the larger, outer can) See diagram # 7. You will need a 49.5 oz food can Use a can opener to take off one of the lids Wash out the can with hot soapy water & use a towel to dry the can completely Take the Old style (triangle tip) steel can opener to puncture 4 holes (equal distance from each other) in the bottom of the can Wrap the can above the 4 holes on the outside of the can with pipe wrap insulator and duct tape this to the can. See diagram #7 Put a Velcro sticky tab in the bottom center of the can. This will stabilize the feedstock holder. 11. Record the initial temperature in degrees Celsius of the water in your data table #3. 3

4 12. Use the lighter to ignite your food sample. BE VERY CAREFUL NOT TO BURN YOURSELF OR ANYONE ELSE. When lighting the Cheetos be sure to light it from the bottom so that the entire piece catches on fire. Make sure there is a stable flame before removing the lighter flame. 13. Make sure to hold the thermometer so that you are NOT adding your own body heat to the temperature reading and DO NOT let the bottom of the probe touch the metal of the can. You only want the temperature readings of the water. 14. When the feedstock sample is no longer burning, stir the water slightly and record the highest (final) temperature ( C) attained in data table # Record the final mass of the feedstock holder and the burned food in data table # Repeat the procedure for the Cheetos and the filamentous algae. You will weigh out the Cheetos to be slightly larger so that you can hollow out a small cavity in the center of the Cheetos to fill with filamentous algae. Weigh your hollowed out Cheetos, weigh your algae. See Diagram #10 below. Follow the underlined & bold faced steps using a fresh quantity of room temperature distilled water for each trial. Repeat the procedure for two more different feedstocks. 17. When you re done collecting all the data put all materials away and clean up your lab stations. 18. Analyze the data collected and record your values in your lab notebook. Diagram #10 Photo by Mary C. Criss Assisted by Mary Claire Carter 4

5 DATA TABLES Table 1: Mass of Feedstock Name Hour Date Feedstock Cheetos Cheetos with Filamentous Algae Sample Initial mass of feedstock and feedstock holder (thimble) Final mass of feedstock and feedstock holder Mass of feedstock burned initial-final Table 2: Mass of H 2 O Heated Mass of HEATED can & H 2 O (g) Mass of EMPTY (top) can (g) Mass of H 2 O HEATED Full can minus empty can 5

6 DATA TABLES (CONTINUED) Table 3: Temperature Change of H 2 O Final temp. of H 2 O (tf) (after it has been heated) Initial temp. of H 2 O (ti) (Before Heating) Temp. Change of water ( t) Final-initial 6

7 Calculations In this project you will learn a method for measuring how much chemical energy is stored in different types of food. You will oxidize the food much more rapidly, by burning it in air. You'll use a homemade calorimeter to capture and measure the heat energy released by burning. The basic idea of a calorimeter is to capture the released heat energy with a reservoir of water, which has a high capacity for absorbing heat. The temperature of the water reservoir is measured at the beginning and at the end of the experiment. The increase in the temperature (in C) times the mass of the water (in g) will give you the amount of energy captured by the calorimeter, in joules. We can write this in the form of an equation: where: q= (Cp)(m)( T) q = heat absorbed, in joules (j) by the water; m = the mass of the heated water, in grams (g); Cp = the specific heat capacity of water, which is joule/gram C; and T = the change in temperature (the final temperature of the water minus the initial temperature of the water), in degrees Celsius ( C). Let's work through an example to make sure that the equation is clear. (We'll use made-up numbers for the example. You'll have to try the experiment for yourself to get actual measurements.) So let's say that after burning the food you have 100 g of water in the calorimeter (m = 100 g). The initial temperature of the water is 20 C. After burning up some small piece of food, we measure the water temperature again, and find that the final temperature is 24 C. Now we have all of the information we need to calculate the amount of heat captured by the calorimeter: q= 100g x joule/g C X 4 C q = 100 x X 4 q= 1,674.4 J Now you divide this by the mass of your food type that was burned (beginning mass ending mass) for this example let s use 1.5 grams. q = 1,674.4 J 1.5 g q= 1, J/g (the amount of energy in the feedstock you burned) 1kilojoule = 1000 joules; so kilojoules /g in this example. 7

8 Now you convert the kj (1.116KJ/g) to Kilocalories (1 Kilocalorie = 1 Calorie written with a capital C = kj = J) 1.116kJ x 1 Calorie = Calories g 4.184kJ g Now you have to calculate the actual Calories / gram reported on the food container. This value is also known as the theoretical value. You have to take into consideration the Calories per serving and the weight per serving (in grams). For example, Brand X cookies has 150 Calories per serving, and 1 serving equals 25 grams. 150 Calories = 6 Calories 25 grams gram Finally, you will calculate the percent error between your experimental value (determined by completing the lab) and the theoretical value that you calculated above. The purpose of calculating the percent error is to determine how close to the true (or theoretical) values, or how accurate, their experimental values really are Percent Error = Experimental value Theoretical value x 100% Theoretical value Experimental value The results (or product) that you got at the end of the lab experiment, the value that you calculated from doing the lab. Theoretical value This value is the calculated results taken from the food label and is also called the accepted or true value. It can often be found in reference tables. For example: A student experimentally determines the specific heat of water to be 4.29 J/g x C o. He then looks up the specific heat of water on a reference table and finds that is 4.18 J/g x C o. What is his percent error? 4.29 J/g o C 4.18 J/g o C x 100% = 2.63% 4.18 J/g o C (Explanation modified from 8

9 Building the Can Calorimeter (photos taken by Mary C. Criss) Diagram #1 Diagram #2 Diagram #3 (top view) Paperclip platform #10 cork Velcro sticky tab Aluminum Foil Thimble Large outer can 4 Air holes at bottom of can Feedstock holder & thimble held in place with Velcro Diagram #4 Diagram #5 (top view) Diagram #6 Aluminum foil lid Wire Hangers 8 fl. Oz. pop can Large outer can Small pop can (8 oz) Bent wire hanger Digital thermometer Aluminum foil lid Diagram #7 Diagram #8 Finished Can Calorimeter Diagram #9 Bomb Calorimeter Large outer can (49.5 oz food can) Wrapped in pipe wrap insulation & covered in Duct tape ects/602/616516/chapter_08.html Create 4 air holes at the bottom of the can using the can opener 9

10 Name Hour Date DATA ANALYSIS: 1. The heat absorbed by the water, q (measured in joules), is determined by: where.cp = the specific heat capacity of H 2 O, 4.18 J/g C q= (Cp)(m)( T) m = the mass of the H 2 O heated, in grams. t = the change in temperature, in degrees Celsius. A. To determine the thermal energy of the feedstock burned, what two quantities for each feedstock do you need from the data tables? Record those two measurements with the appropriate units. m T q B. Put your final answer in kj (HINT: 1kJ = 1,000J). SHOW YOUR WORK Heat, q, in kj 2. From the number calculated in step 1B and the information in the data table, calculate the energy content PER GRAM of feedstock that was burned. Energy content / gram 10

11 3. You can calculate the number of calories in your feedstock sample since you know that one Calorie raises the temperature of one kilogram of H 2 O by one degree Celsius. Also, there are 4.18kJ in one Calorie. What is the energy content for each feedstock sample expressed in Calories? (HINT: 1 Cal = 4.18kJ) Calculated Calories = Experimental value Calculated Calories, per gram 4. Now, record the actual Calories per gram of each feedstock. To do this you will need to bring your calculations up to the teacher and check the feedstock calories chart. Actual Calories = Theoretical value Actual Calories, per gram 5. Calculate the percent error. Percent Error = Experimental value Theoretical value x 100% Theoretical value Percent error 11

12 6. Calculate the energy content for the filamentous algae in Calories / gram. To do this you will simply take the Cheetos Calories / gram minus the Cheetos & filamentous Algae s Calories / gram. Filamentous Algae Energy content in Calories / gram 12

13 Name Hour Date Calorimeter Design Analysis Use the diagrams and descriptions of the bomb calorimeter (Diagram # 9) and the can calorimeter (Diagrams #1 - #8) to determine the key characteristics of each and list your ideas in the Venn diagram below. Key Similarities Venn diagram of Calorimeter Characteristics Can Calorimeter Key Differences 13

14 Name Bomb Calorimeter Student Design Calorimeter Hour Date Analysis Questions: 1. Identify the system in your lab set up; name specific object(s). Also, identify the surroundings in your lab set up. (Anything in the environment that may affect your results.) Draw and label diagrams of the set up. 2. Did energy enter or leave the system in this lab? Briefly explain and draw a diagram of this heat transfer. 3. Add your results to your data chart. Look at other group s results also. a. What kinds of feedstock(s) have the highest energy content? b. The lowest energy content? 4. What are the limitations of this calorimeter in determining the energy content of the different feedstock? 5. Can you think of anything that would make it better? Describe and draw diagrams of how you could improve the setup of this lab. 14

15 6. Error analysis a. Were your calculated values of heat released per gram (Cal/g) lower or higher than the literature values? b. Use the chart of similarities and differences between a true bomb calorimeter and our can calorimeter to discuss at least three possible reasons why your values are different from the literature values 7. Design your ideal Calorimeter and test it out using the same feedstock used in the Can Calorimeter. On another sheet of paper, include detailed drawings of your calorimeter. Then build it and test it out using the same feedstock and procedures as the can calorimeter. 8. Compare and Contrast your design to the Can Calorimeter design. 9. Compare and Contrast your data to the Can Calorimeter data 15

16 Teacher Information Calories Reference Table Feedstock Amount (1 serving) Calories / serving Sunflower 1 cup w/ hulls, edible yield (242.8g) 269 Raw Peanut 1 oz (28.3g) 160 Safflower Seed kernels dried 1 oz (28.3g) 146 Soy Bean (manufactured by O Organics) ½ cup (121.4g) 140 Cheetos 28 g / serving 160 Calorie Counter website: References Burning Food and Fuel Lab %2Flib%2F %2FBurning_Food_and_Fuel_LabR3.doc&rct=j&q= %2F...%2FBurning_Food_and_Fuel_LabR3.%20..%5D&ei=Q6kbTvrRDpO40AH5x6XABw&usg=AFQjCNHbYViLuaobXrN YV1K7GEKrFKdRYg Randall Frost, Ph.D. Producing Algal Oil Robert Lucas, Lab: nut Calorie measurement. Chemistry Lab: Food Calorimetry Andrew Olson, Ph.D., Science Buddies, USC Biology Department, " 'Burning Calories': The Energy in Food," Biology Department, University of Southern California [accessed January 18, 2006] fall/documents/bisc150-lab_burningcal.pdf. Gardner, R., Science Projects About Kitchen Chemistry. Berkeley Heights, NJ: Enslow Publishers, Calorie Counter website: 16