Overview for the Biofuels Unit

Transcription

1 verview for the Biofuels Unit This set of three laboratory experiments introduces students to biofuels. These labs, which can be run in three consecutive weeks, give students the opportunity to explore the chemical properties of biofuels from three different perspectives. During the first week students are introduced to toxicology, including the use and limitations of LD 50 values. Students then make up standard dilutions of various biofuels and set up a simple germination assay to quantify the potential ecotoxicty of each of the fuels. The second week of the unit has the students synthesize biodiesel from soybean oil. In addition to introducing techniques of synthetic chemistry, this lab focuses on concepts of stoichiometry, limiting reagents, and reaction yield. The synthesis of biodiesel can be set up in less than an hour, and the rest of the lab period is used to collect the data from the germination experiment which has been incubating for a week. The final lab of the unit challenges students to determine the heat of combustion of their biodiesel using a simple soda can thermometer. This lab introduces heat transfer and asks students to consider the relationship between the heat of combustion of a fuel and efficiency of a fuel. The themes of the unit are synthesized by the students in a final assignment. The students are asked to write a short paper evaluating biodiesel and one other biofuel as alternative transportation fuels. They are told to use data they collected along with supporting information from scientific sources to support their conclusions. This short paper gives students a chance to reflect on what they have learned and see how it applies to the energy challenges facing our society. Timeline: Week 1- Set up germination assay Week 2- Run biodiesel reaction - Collect data from the germination assay Week 3- Conduct separation and purification of biodiesel - Determine the Heat of Combustion for biodiesel

2 Dose Makes the Poison: Estimating the Relative Ecotoxicity of Various Biofuels "All things are poison and nothing is without poison; only the dose makes a thing not a poison." - Paracelsus ( ) Chem Connections: The central theme of green chemistry is the design of materials and processes that are inherently safer for human health and the environment. In order to achieve this goal, we need to be able to quantify how harmful or toxic a substance is to humans or the environment. There are many different ways to quantify the toxicity of a chemical. The most common is the mean lethal dose, or LD 50. This is the amount of a chemical substance that it takes to kill half the members of a test population for a given exposure and amount of time. The LD 50 is usually expressed with units of amount of chemical/weight of animal, so that values can be compared between different size animals. For example the LD 50 for sodium cyanide is 6.3 mg/kg. This means that if you give 6.4 mg of sodium cyanide to a 1 kg rat, it has a 50% chance of dying as a result of that exposure. The mean lethal dose for a 60 kg human would be 6.4 mg/kg 60 kg = 380 mg. The first activity in this experiment will give you a chance to examine more of these values for various chemical substances. It is important to realize that the LD 50 is not the only measure of chemical toxicity. There are many other possible outcomes from chemical exposure that are less severe than death, but that are still of concern. These include the chemical s ability to cause cancer, disrupt hormone function, or cause birth defects. In order to quantify these affects one current testing method uses large numbers of laboratory animals, many years, and millions of dollars. These methods have been criticized by many animal rights groups and others as being wasteful and inaccurate. In response to these shortcomings many scientists, companies, and governments are developing new methods to evaluate toxicity. In today s lab we are going to measure how various chemicals affect the germination of plants. We have chosen this test system because we can obtain quantitative data over the course of a week, rather than the many weeks, months, or years that it takes to evaluate chemical exposure in animals. We will be examining various chemicals that have been suggested for use as alternative fuels. All of the fuels we will be testing can be derived from plant resources, and include biodiesel, methanol, ethanol, and 2-butanol.

3 Prelab Activity ften chemists rely on published safety information, rather than experiments to determine the risks associated with chemicals. There are many sources for this information; the most common is the Material Safety Data Sheet (MSDS). For the following three chemicals, you will need to find safety information using a few of the common resources available to chemists. Look up each of these chemicals in each resource, and then answer the following questions. Chemicals: 1) Bisphenol A (BPA) chemical name: 4,4'-dihydroxy-2,2-diphenylpropane a. This is the chemical which has created the public concern over plastic water bottles. 2) Lead (Pb) a. Recently found in children toys. 3) Dioxins class of chemicals. In particular look up 2,3,7,8-tetrachlorodibenzo-pdioxin a. This chemical is why you should not burn plastic, and is one of the few chemical restricted by the EPA. For each of these chemicals find safety information using the following resources: 1) MSDS: From any UC campus computer you can search the UC database at Another way to quickly find a MSDS is to do a google search for: msds chemical name. 2) Wikipedia, yes I want you to use Wikipedia. 3) ChemSpider: This is a website hosted by the Royal Chemical Society: Questions: 1) Which of the three chemicals would you consider most hazardous? Why? 2) What precautions should you take, if you were using each of these chemicals? Which resource gave you this safety information? 3) Is there safety information that is missing from these resources that you would like to have before working with these chemicals? Is so, what information would you like? 4) Which sources of information are you most likely to use in the future? Why?

4 Experimental Procedure Exercise 1: Become familiar with LD 50 Chemicals with large LD 50 values are less likely to harm animals than chemicals with small LD 50 values. LD 50 values are expressed as the amount of chemical administered (usually expressed in mg) divided by the mass of the animal (usually expressed in kg). For example the LD 50 value for the sodium cyanide is 6.4 mg/kg, while the value for vitamin C is 11,900 mg/kg. So we would expect that it would take less than ½ a gram of sodium cyanide to kill a 150 lb human, while it would take more than 1.5 lbs of vitamin C to kill a human. For the following table fill in the missing values, and then answer the questions below: Chemical Name Structure LD 50 (mg/kg) Sodium Nitrite (NaN 2 ) 180 Arsenous Acid (As(H) 3 ) 14 Estimated Lethal Dose for a 60 kg human Aspirin (acetylsalicylic acid) g Sodium Cyanide (NaCN) Polonium Mercury (II) Chloride (HgCl 2 ) Tylenol (acetaminophen) mg 60 mg 1) Rank the substances from most to least acutely toxic. 2) Guess which substance claims the most human lives every year? Explain your reasoning. 3) Doctors have recommended against giving children aspirin, and instead recommend acetaminophen. How many 500 mg tablets of aspirin would it take to reach the LD 50 threshold for a 22 lb (10 kg) child? How many 500 mg tablets of acetaminophen?

5 Exercise 2: Estimate the Ecotoxicity of biofuels using a seed germination assay. This Exercise will take place over 2 lab sessions. During the first you will prepare your samples and solutions. The data collection and analysis will then occur during the second lab period after you set up the biodiesel synthesis. The Approach Work in groups of 2. Equipment needed: 6 plastic petri dishes with covers 12 filter papers large enough to cover bottom of petri dishes 300 Lettuce or Radish seeds Parafilm to seal each petri dish (6 pieces, squares in length) Scissors to cut filter paper Ruler with mm (needed for day two) Chemicals Needed: Deionized Water Biofuels of interest Ethanol Biodiesel (Methyl Linoleate) 2-Butanol Methanol Biofuel Ethanol Biodiesel (Methyl Linoleate) Structure Molar Mass (g/mol) Density of pure biofuel (g/ml) 2-butanol Methanol

6 Part 1- Sample preparation 1. btain six plastic petri dishes, 12 filter papers, and 300 radish seeds. (300 radish seeds should weigh about 2 grams.) 2. Prepare the dishes by putting a piece of filter paper and 50 seeds into each dish. If necessary, cut the filter paper to completely cover the bottom of the petri dish. The seeds should be evenly distributed on the filter paper then cover the seeds with a second piece filter paper. 3. Make a 10% solution of your fuel of interest. In a graduated cylinder, place 2 ml of fuel and dilute with 18 ml of water. Transfer this solution to a 50 ml beaker. (Note: Some residual fuel will remain in the graduated cylinder if you are using biodiesel. Get as much as possible into your beaker and put it on a stir plate and stir very rapidly to make an emulsion. The emulsion should appear cloudy.) 5. Transfer exactly 10 ml of your 10% solution to the first petri dish using the same graduated cylinder. Be sure to label the lid of this petri dish 10% 6. Add 10 ml of deionized water to the remaining 10 ml of the 10% solution. You have now made a 5% solution. The technique of diluting a solution with a known quantity of solvent, is called serial dilution. If you double the volume of a solution, you divide the concentration by If your solution has separated be sure to recreate the emulsion by stirring. 8. Now take 10 ml of your 5% solution and add it to the second petri dish. Don t forget to label the dish! 9. Now continue the serial dilution by adding 10 ml of deionized water to the remaining 5% solution, making it a 2.5% solution. And then add ½ the volume to the next petri dish, label, and repeat for the remaining 2 petri dishes. 10. In the end you will have petri dishes labeled 10%, 5%, 2.5%, 1.25%, and 0.625% 11. In the final petri dish, add 10 ml of deionized water. This will be your control sample, and will be used to compare to all of the other samples. 12. Seal all of the petri dishes with parafilm to reduce evaporation of your solutions and store the petri dishes in your lab drawer until the next lab period.

7 Part 2: Data Collection Complete the data tables below. Table 1: Germination 1. Count the number of seeds germinated in each dish, then calculate the percentage that germinated. Control 0.6% 1.25% 2.5% 5% 10% # of Seeds Germinated (count) Percentage Germinated/ Total Table 2: Root Elongation for germinated seeds 1. For the root elongation, only count seeds that germinated. 2. Measure the root, not shoot or seed body, to the nearest mm. Record the lengths in your lab notebook. You will need these values. 3. If the root is bent, try rolling it along the ruler to estimate the length. 4. If the roots break, do your best to still do the measurement. 5. Use excel or a graphing calculator to obtain the average and the standard deviation for each concentration. Control 0.6% 1.25% 2.5% 5% 10% Average root length of Seeds which Germinated (mm) Before leaving lab write your percent germination and average root length values on the chalk board.

8 Post lab Questions: 1) Graph the percent germination class data using a program like Excel or using graph paper. Make a separate graph for each fuel. Express the percent of seeds germinated as the percent biofuel in solution increases. Also include a plot of the class averages. EXAMPLES! 2) Compare the results for each of the biofuels examined in your lab section. Based on the data, which fuel seems to be the most toxic to seeds? Do the fuels effect both germination and root growth in the same fashion? 3) Express the percentage solution values in units of molarity (mol/l). Compare the molarity of the 10% solutions for each of the biofuels used in your lab sections. Does knowing the molarity of each of these solutions change your opinion of which fuel is most toxic? Why? Suggest additional experiments to support your conclusions. 4) Look up the LD 50 values for each of these fuels, how do the LD 50 values compare to the trend you saw in class? The LD 50 value for biodiesel is hard to find, because the LD 50 values are considered to be higher then the threshold for harm in the species tested. In other words, the toxicity of biodiesel is insignificant. (Remember that LD 50 values are a measure of animal, not plant toxicity!)

9 Bibliography This lab was inspired by the work done by faculty and students at Gordon College, who kindly shared their material on the GEMS database. 1) Soo Y. Kwon, Irvin J. Levy, Matthew R. Levy, Daniel V. Sargent, Dwight J. Tshudy, and Marissa A. Weaver, "The dose makes the poison: Measuring ecotoxicity using a lettuce seed assay" Department of Chemistry Gordon College. GEMS database Background reading for the LD 50 values can be found in the following sources. 2) Timbrell, J. Introduction to Toxicology, CRC Press: New York, ) Girard, J. Principles of Environmental Chemistry 2 nd ed., Jones and Bartlett Press: Boston Mass. 2010, Chapter 16.

10 Synthesis of Biodiesel Chem Connections: The diesel engine was first designed by Rudolf Diesel in The original diesel engines had two key design features. First they used heaver fuels, in other words, fuels with longer carbon chains. Typical gasoline engines use saturated hydrocarbons with 7-11 carbon atoms per chain (high octane fuel). Diesel engines use fuels with longer chains, often containing between carbon atoms. Rudolf Diesel envisioned running his diesel engine with vegetable oil, which contains three chains that are carbons long (See Figure 1: octane, soybean oil, and petroleum diesel, biodiesel). His design became a reality in 1900, when the first diesel engines where produced and used peanut oil as a fuel source. The second distinguishing feature of a diesel engine is that the fuel ignites without using a spark system. Compression of air before injection of the fuel creates heat, which ignites the fuel in a diesel engine. This is a great application of the ideal gas law! This simple design allows engines to operate with higher efficiency than traditional gasoline engines which rely on spark plugs to ignite the air/fuel mixture. These two design features, multiple fuel sources and higher efficiencies, have stimulated the resurgent interest in diesel engines. Biodiesel can be used in engines designed to run on petroleum diesel, making biodiesel an attractive renewable fuel. Biodiesel can be produced from many vegetable oil sources, and can even be made from oil which has already been used for cooking. This means that the 1-3 billion gallons of frying oil used in the US every year could be used to power vehicles instead of ending up in land fills or sewers! CH H 3 C 3 CH 3 C CH C CH H 3 C 3 H 2 Isooctane (in gasoline) H 2 C HC H 2 C CH 2 CH CHCH 2 CH CHCH 2 CH 3 CH 2 CH CHCH 2 CH CHCH 2 CH 3 CH 2 CH CHCH 2 CH CHCH 2 CH 3 Glyceryl trilinoleate (in soybean oil) H 3 C C H 3 C H C C H 2 H C CH H 2 C H C H 3 C H 2 C CH3 H 3 C CH 2 CH CHCH 2 CH CHCH 2 CH 3 Dimethyldecadiene (in diesel) Methyl linoleate (in biodiesel) Figure 1: Primary Components in Common Fuels. The fuels currently used in combustion engines are all complex mixtures. The primary component of each fuel is shown above.

11 This experiment will give you the opportunity to make some biodiesel starting from vegetable oil. If you trust your chemistry skills you could even put your product from this lab into any diesel car. During the next experiment you will get to see how this fuel burns. New Chemistry In order to make biodiesel from naturally occurring oils the long chain hydrocarbons must be chemically separated. This can be accomplished through a process called hydrolysis. In your body this is the first step in the digestion of fats and oils in our diet. H 2 C HC H 2 C CH 2 CH CHCH 2 CH CHCH 2 CH 3 CH 2 CH CHCH 2 CH CHCH 2 CH 3 CH 2 CH CHCH 2 CH CHCH 2 CH H 2 3 H CH 2 CH CHCH 2 CH CHCH 2 CH 3 Fatty Acid (linoleic acid) + H H CH H C C H 2 H 2 Glycerol Figure 2: This process of breaking down oil into fatty acids and glycerol (also known as glycerin) proceeds very slowly without the addition of catalysts. Notice that the reaction in figure 2 is balanced. By adding water the bonds between the fatty acid chains and the glycerol have been broken. This process proceeds very slowly without the addition of a catalyst. However, the hydrolysis reaction can be catalyzed by the addition of either an acid or a base (this is one of the reasons your stomach is an acidic environment). The product of the hydrolysis reaction is a carboxylic acid, attached to the long-chain hydrocarbon. Although this looks a lot like the biodiesel shown in figure 1, the carboxylic acid can be corrosive inside an engine. For this reason, chemists have devised another way to chemically modify the chains found in natural oils. This new way is shown in Figure 3 below. Notice that instead of water, methanol is used along with NaH, which is a strong base that will act to catalyze the reaction. No water is used and the desired product of the reaction belongs to a class of chemicals called esters. Esters are like carboxylic acids, but instead of having the form RCH, esters are terminated with a carbon chain RCR. Notice that esters were present in the original soybean oil. Since we changed one ester into another ester, this reaction is called a transesterification. What physical properties would change when the soybean oil is changed to three separate esters? CH 2 CH CHCH 2 CH CHCH 2 CH 3 3 H H 2 C 3 C NaH HC CH 2 CH CHCH 2 CH CHCH 2 CH + 3 H 3 3 C H H 2 C CH 2 CH CHCH 2 CH CHCH 2 CH 3 Figure 3: The process we will use to produce biodiesel from soybean oil. CH 2 CH CHCH 2 CH CHCH 2 CH 3 biodiesel (methyl linoleate) + H H CH H Glycerol C C H 2 H 2

12 In addition to the desired biodiesel, this reaction also creates the byproduct glycerol. Before the biodiesel can be used for combustion, the glycerol will have to be separated from the biodiesel. This is relatively easy because the two chemicals are immiscible (they do not mix) and they have significantly different densities. Biodiesel has a density of g/ml and glycerol has a density of g/ml. This means that the biodiesel will float on top of the glycerol. Prelab Questions 1) Complete the table below for all of the reactants and products used in this experiment. Chemical mp ( o C) bp ( o C) or smoke point density (g/ml) at 25 C Molecular Weight (g/mol) Hazards soybean oil methanol sodium hydroxide methyl linoleate (biodiesel) glycerol water 2) If you have 10.0 kg of oil that you want to turn into biodiesel, how many liters of methanol will you need? Use the balanced equation in Figure 3 and the molecular weight for soybean oil to complete the calculation.

13 Experimental Procedures Today you will be making biodiesel and you will be collecting data from the seed germination experiment. ½ the class will start by running the biodiesel reaction, while the other ½ gets starting collecting germination data. Then you will switch. The Problem Produce biodiesel from soybean oil, and compare the properties of biodiesel to other fuels. The Approach Work in groups of 2 or three to synthesize the biodiesel. Equipment needed: 250 ml Erlenmeyer flask 50 ml Beaker 100 ml Beaker Graduated Cylinder Magnetic stir bar Heating and Stirring Plate Thermometer ( o C) Parafilm to cover the 50 ml beaker while being stored Chemicals Needed: 0.4 M solution of NaH in methanol Soybean or other vegetable oil Day 1 1. Note: Remember that water and vegetable oil reacts to form the unwanted fatty acid product, so please use all clean and dry glassware for this experiment. 2. Use a graduated cylinder to measure 40 ml of soybean oil (vegetable oil). Transfer the oil in a 250 ml Erlenmeyer flask and warm the oil to between 40 and 50 o C while rapidly stirring with a magnetic stir bar. (Note: For both your safety and the effectiveness of the reaction do not allow the temperature to exceed 50 o C. 3. Turn off the heat. 4. Add 10 ml of the 0.4 M sodium hydroxide in methanol solution to the warm oil. 5. Stirring the reaction for 45 minutes.

14 6. Stop the stirring and pour the mixture into a 50 ml beaker. Allow the mixture to cool and then cover the beaker with parafilm. Label the beaker with your name and date. 7. You will store the mixture in the lab drawer until next week, which will give ample time for the layers to separate. Note: Use the remainder of your lab time to count the seeds in the germination experiment started during the last lab period. Directions and tables for this data collection can be found in the previous experiment! Day 2 1. By comparing the densities for each of the products, identify the biodiesel layer. (Remember liquids that are less dense float on liquids that are denser.) Determine the amount of biodiesel in ml. Record this value in your lab notebook. 2. Transfer the biodiesel to a 100 ml beaker. 3. Dry your biodiesel by heating the biodiesel at 80 o C while stirring for 20 min. Heating your sample will generate methanol vapors and other fumes, so this MUST be done in the fume hood. 4. Measure the volume of your final isolated biodiesel. Record this value in your notebook.

15 Postlab Questions 1) Determine the limiting reagent in your synthesis of biodiesel. 2) What is the theoretical yield for this reaction? 3) Calculate your actual yield based on the amount of biodiesel you isolated after heating to remove residual methanol. Calculate the actual yield of biodiesel based on the amount of biodiesel before separation and heating. Use this table to answer the following questions. Fuel mp ( o C) bp ( o C) or smoke point density (g/ml) at 25 C viscosity (mpa s) at 25 C Soybean il Biodiesel Gasoline (isooctane) Petroleum diesel ) If you had four containers without labels one biodiesel, one veggie oil, one petroleum diesel, one gasoline what experiments would you have to run to differentiate them? 5) How would you expect the viscosity of fuel to affect its performance on a cold day (think about -20 o C in the winter in Minnesota)? Which of the fuels listed in the table above would work best on a cold day?

16 Bibliography Numerous versions of this lab are available in the chemical education literature and can be found online. ur development was informed by the versions listed below. 1. John E. Thompson, "Biodiesel Synthesis" Lane College 2006 GEMS database, follow-up personal communication, Amy Cannon, "Green Chemistry in the Curriculum: Biodiesel Module" Beyond Benign and Fisher science education, downloaded Ehren C. Bucholtz, Biodiesel Synthesis and Evaluation: An rganic Chemistry Experiment J. Chem. Ed. 2007, 84,

17 Biodiesel Heat of Combustion and Energy Efficiency Chem Connections: The heat of combustion is the amount of heat energy released when a substance is completely burned. From a chemical perspective, burning is the complete oxidation of a chemical. For example, a hydrocarbon is completely burned when all of the carbon atoms have be transferred to C 2 and the hydrogen atoms have turned into H 2. Consider a relatively simple case, the burning of methane (the primary component of natural gas). H H C H H C H 2 H f (kj/mol) = The amount of energy produced by this reaction can be calculated by summing the bond energies of each of the products ( H f is the heat of formation in kj/mol), and by subtracting the sum of the H f for the reactants. (When you are looking these values up you should always use the values assuming your products are in the gas phase.) The heat of combustion for this reaction is: (-242) (-75) = -803 kj/mol. Remember that the negative sign indicates that this energy is given off, so this is an exothermic reaction that will produce 803 kj/mol. That energy can then be used to do work. Last week we discussed a few of the possible advantages of biodiesel, this week we want to consider the concept of efficiency from a chemical point of view. It was mentioned that diesel engines are more efficient than gasoline engines. Rather, diesel engines convert heat energy to mechanical energy more efficiently than gasoline engines. This week we want to determine how efficiently various chemical fuels produce heat energy. This can be done by determining the heat of combustion for a given fuel. In addition to calculating the amount of heat produced by a reaction, we can also measure the amount of heat using a technique called calorimetry. Calorimetry is a general term for a number of techniques used to measure heat. In today s lab we are going to use a very simple setup to measure the amount of heat produced when we burn our biodiesel. It is very hard to measure the heat produced by burning fuel directly, so we will use the heat produced to heat water. It takes 4.18 J of energy to raise 1 g of water 1 o C. For example, consider heating 200 g of water from 25 o C to 35 o C. This is a change of 10 o C. So to find the energy that this change took, we multiply (10 o C)(200 g)(4.18 J/g o C)= 8,360 J or 8.4 KJ. If it took 0.3 g of fuel to heat the water, then we can determine the heat of combustion by dividing (8.4 KJ)/(0.3g)= 27.8 KJ/g. So, by measuring both the temperature increase in the water and how much fuel is used, we can determine the heat of combustion.

18 Prelab Questions 1) It was mentioned that diesel engines take advantage of the ideal gas law (PV=nRT) to create the conditions for combustion. Calculate the temperature inside a piston which compresses air at room temperature and pressure (298 K, 1 atm) with a volume ratio of V 1 /V 2 = 15/1. The final pressure in the piston is 30 atm. How hot is the air after compression? 2) For the fuels listed below, calculate the theoretical heats of combustion using the H comb = H f, products - H f, reactants. Assume that 1 mole of the fuel burns completely to give C 2 and H 2. Finally, convert this value to energy density (kj/g) which is the unit we will be measuring in today s lab. Fuel Formula Heat of Compustion (kj/mol) Energy Density (kj/g) Fuel H f (kj/mol) Isooctane C8H18 Gasoline Hydrogen H2 biodiesel Ethanol C2H5H Soybean oil Mythyl Linoleate (biodiesel) C19H342 Soybean oil C57H1006 3) Calculate the final temperature for 225 g of water, which starts at 20 o C, after 0.75 grams of biodiesel have to be burned to heat the water. Assume all of the energy goes to heating the water.

19 Experimental Procedure The Problem Determine the heat of combustion for biodiesel using ethanol as a standard to calibrate your calorimetry apparatus. The Approach Work in groups of 2. Equipment needed: il Lamp with a wick Ring Stand Metal container for water with wire to suspend from the ring stand Thermometer ( o C) Access to an analytical balance Chemicals Needed: Biodiesel (from last week) Ethanol PREPARING BIDIESEL FR CMBUSTIN 1) Complete the separation and purification of your biodiesel from last lab period. Directions can be found in lab manual Synthesis of Biodiesel under the DAY 2 heading. MEASURING HEAT TRASNFER 2) nce the biodiesel has been isolated and purified, fill an oil lamp with ~15 ml of your biodiesel. Then put the wick holder into the biodiesel, making sure that the wick is exposed to fuel along the entire length. (If the wick is not completely whetted by the fuel, it will not burn correctly.) 3) Make a precise measurement of the total weight of your lamp + biodiesel. Record this starting weight. 4) Add exactly 225 ml of water into a soda can calorimeter. Be careful to use the exact same amount of water in each measurement. 5) Suspend the metal can from the ring stand and measure the temperature of the water. Record this temperature. 6) If the temperature is less than the temperature in the room, allow the water to warm to room temperature before starting your experiment. 7) nce the temperature of the water has equilibrated with the room, light the oil lamp and make sure it is placed as close to the metal can as possible, so that the tip of the flame is slightly below the bottom of the can. 8) Monitor the change in temperature with your thermometer, while also gently stirring the water to insure even heat distribution.

20 9) nce the temperature of the water has raised about 10 o C, extinguish the flame. 10) Check the temperature again, if it continued to increase after the flame was extinguished, record the highest temperature. 11) Weigh the oil lamp again, recording the final weight. 12) Calculate the amount of oil used to raise 225 ml to heat the water. 13) Now repeat this procedure at least two more times so that you are able to average your data. Each time start with fresh water at room temperature. Also make sure you record the starting and ending weight of the fuel + lamp. 14) Now repeat the same procedure with ethanol. 15) Repeat the measurement at least 3 times so that you will be able to average your data. Data and Calculation Fuel EtH EtH EtH EtH EtH Biodiesel Biodiesel Biodiesel Biodiesel Biodiesel grams burned moles burned Tinitial Tfinal T The ethanol experiment will give us a sense of how much heat the calorimeter itself will absorbs from the burning flame. We can then use this data to calibrate our calorimetry based on ethanol s heat of combustion. The best way to determine the heat of combustion for a reaction is to use a bomb calorimeter, where all of the heat from the combustion reaction is trapped inside a closed system. In this system the amount of heat absorbed by the calorimeter is given by the equation: q cal = C cal X T C cal is the heat capacity for the entire bomb calorimeter. And is expressed in the units kj/ºc. This value must be determined experimentally for the calorimeter and is based on the amount of heat that both the water and the surroundings absorb. This will be true for our calorimeter as well. In order to calculate C cal for our soda can calorimeters we will use the known value for the combustion of ethanol. ( H comb, EtH = kj/mol EtH) Since q cal is the

21 amount of heat aborbed during the reaction it will have a positive value for exothermic reactions, and will be equal to q combustion. q cal = -q combustion = C cal X T -q combustion = H comb X (moles EtH) ( H comb X (moles EtH))/ T = C cal Calculate C cal for your calorimeter using the combustion data you gathered for from the burning of Ethanol. Reaction Ccal EtH 1 EtH 2 EtH 3 Average Then use the q cal expression to calculate the H comb for the biodiesel that you made last week. Reaction Biodiesel 1 Biodiesel 2 Biodiesel 3 Average H comb Postlab Questions 1) Compare the values you measured for biodiesel, to the predicted values you calculated in the prelab. Do they match? If not explain, why they don t and suggest ways that the experiment could be improved. 2) The heat of combustion for biodiesel is a measure of chemical energy. Explain the relationship between chemical energy and fuel efficiency. Does a higher heat of combustion for a fuel mean it is more efficient? Explain what contributes to fuel efficiency.

22 Bibliography This lab was inspired by following experiments. 1) Stephen M. Akers, Jeremy L. Conkle, Stephanie N. Thomas, and Keith B. Rider. "Determination of the Heat of Combustion of Biodiesel Using Bomb Calorimetry" J. Chem. Ed. 83, 2006, ) American Chemical Society, Chemistry in Context Laboratory Manual. 6 th ed. McGraw-Hill Science, In particular a personal communication with Jennifer Tripp, an editor for the newest version of these labs.

23 Report for the biofuels unit In addition to answering all of the post lab questions, please prepare short paper for these three labs which examines various biofuel alternatives. Your short paper (1-2 pages) should compare and contrast two or more of the fuels sources that you have studied during the last 3 weeks. You should consider the sources, synthesis, health effects, and efficiency of the fuel sources in the paper. Finally, include a recommendation for or against the use of one or more of the fuels you choose to discuss. Evaluation of this report will be based on your ability to discuss the biofuels using data you collected from lab or found in other scientific references. Recommended Reading: 1) Howard Wolinsky, The Economics of Biofuels, European Molecular Biology rganization Reports, 10, , doi: /embor ) Melinda Wenner, The next Generation of Biofuels, Scientific American, March 2009, (