GreenChemistry Biofuels Unit

8/12/2019 GreenChemistry Biofuels Unit

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Overview 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 thechemical properties of biofuels from three different perspectives. During the first weekstudents 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 simplegermination 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. Inaddition to introducing techniques of synthetic chemistry, this lab focuses on concepts ofstoichiometry, limiting reagents, and reaction yield. The synthesis of biodiesel can be setup in less than an hour, and the rest of the lab period is used to collect the data from thegermination experiment which has been incubating for a week.

The final lab of the unit challenges students to determine the heat of combustion of theirbiodiesel using a simple soda can thermometer. This lab introduces heat transfer and asksstudents to consider the relationship between the heat of combustion of a fuel andefficiency of a fuel.

The themes of the unit are synthesized by the students in a final assignment. The studentsare asked to write a short paper evaluating biodiesel and one other biofuel as alternativetransportation fuels. They are told to use data they collected along with supportinginformation from scientific sources to support their conclusions. This short paper givesstudents a chance to reflect on what they have learned and see how it applies to theenergy challenges facing our society.

Timeline:Week 1- Set up germination assayWeek 2- Run biodiesel reaction

- Collect data from the germination assayWeek 3- Conduct separation and purification of biodiesel

- Determine the Heat of Combustion for biodiesel


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Dose Makes the Poison: Estimating theRelative Ecotoxicity of Various Biofuels"All things are poison and nothing is without poison; only the dose makes a thing not a

poison."- Paracelsus (14931541)

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 theenvironment. There are many different ways to quantify the toxicity of a chemical. Themost common is the mean lethal dose, or LD 50. This is the amount of a chemicalsubstance that it takes to kill half the members of a test population for a given exposureand amount of time. The LD 50 is usually expressed with units of amount ofchemical/weight of animal, so that values can be compared between different sizeanimals. For example the LD 50 for sodium cyanide is 6.3 mg/kg. This means that if yougive 6.4 mg of sodium cyanide to a 1 kg rat, it has a 50% chance of dying as a result ofthat 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 ofthese values for various chemical substances.

It is important to realize that the LD 50 is not the only measure of chemicaltoxicity. There are many other possible outcomes from chemical exposure that are lesssevere than death, but that are still of concern. These include the chemicals ability tocause cancer, disrupt hormone function, or cause birth defects. In order to quantify theseaffects 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 groupsand others as being wasteful and inaccurate. In response to these shortcomings manyscientists, companies, and governments are developing new methods to evaluate toxicity.

In todays lab we are going to measure how various chemicals affect thegermination of plants. We have chosen this test system because we can obtainquantitative data over the course of a week, rather than the many weeks, months, or yearsthat it takes to evaluate chemical exposure in animals. We will be examining variouschemicals that have been suggested for use as alternative fuels. All of the fuels we will betesting can be derived from plant resources, and include biodiesel, methanol, ethanol, and2-butanol.


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Experimental ProcedureExercise 1: Become familiar with LD 50

Chemicals with large LD 50 values are less likely to harm animals than chemicals withsmall 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 forvitamin C is 11,900 mg/kg. So we would expect that it would take less than a gram ofsodium cyanide to kill a 150 lb human, while it would take more than 1.5 lbs of vitaminC 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)

Estimated Lethal Dose for a

60 kg human

Sodium Nitrite (NaNO 2) 180

Arsenous Acid(As(OH) 3)

14

Aspirin (acetylsalicylicacid) 200 12 g

Sodium Cyanide(NaCN) 380 mg

Polonium-210 0.00001Mercury (II) Chloride

(HgCl 2)60 mg

Tylenol(acetaminophen) 1944

1) Rank the substances from most to least acutely toxic.

2) Guess which substance claims the most human lives every year? Explain yourreasoning.

3) Doctors have recommended against giving children aspirin, and insteadrecommend acetaminophen. How many 500 mg tablets of aspirin would it take toreach the LD 50 threshold for a 22 lb (10 kg) child? How many 500 mg tablets ofacetaminophen?


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Exercise 2:Estimate the Ecotoxicity of biofuels using a seed germination assay. This Exercise willtake place over 2 lab sessions. During the first you will prepare your samples andsolutions. The data collection and analysis will then occur during the second lab periodafter you set up the biodiesel synthesis.

The ApproachWork in groups of 2.

Equipment needed:6 plastic petri dishes with covers12 filter papers large enough to cover bottom of petri dishes300 Lettuce or Radish seedsParafilm to seal each petri dish (6 pieces, 2-2.5 squares in length)Scissors to cut filter paper

Ruler with mm (needed for day two)Chemicals Needed:Deionized WaterBiofuels of interest

EthanolBiodiesel (Methyl Linoleate)2-ButanolMethanol

Biofuel Structure

Molar

Mass(g/mol)

Density of

pure biofuel(g/mL)Ethanol 46.07 0.789

Biodiesel(MethylLinoleate)

294.47 0.889

2-butanol 74.12 0.808

Methanol 32.03 0.791


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Part 1- Sample preparation1. Obtain six plastic petri dishes, 12 filter papers, and 300 radish seeds. (300 radish seedsshould 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 seedsshould be evenly distributed on the filter paper then cover the seeds with a second piecefilter paper.

3. Make a 10% solution of your fuel of interest. In agraduated cylinder, place 2 mL of fuel and dilute with 18mL of water. Transfer this solution to a 50 mL beaker.

(Note: Some residual fuel will remain in the graduated cylinder if you are usingbiodiesel. Get as much as possible into your beaker and put it on a stir plate and stir veryrapidly 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 samegraduated 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 havenow made a 5% solution. The technique of diluting a solution with a known quantity ofsolvent, is called serial dilution. If you double the volume of a solution, you divide theconcentration by 2.

7. 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. Dont forgetto label the dish!

9. Now continue the serial dilution by adding 10 mL of deionized water to the remaining5% solution, making it a 2.5% solution. And then add 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 controlsample, 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 andstore the petri dishes in your lab drawer until the next lab period.


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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 thatgerminated.Control 0.6% 1.25% 2.5% 5% 10%

# of SeedsGerminated(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 inyour 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 rootlength ofSeeds whichGerminated(mm)

Before leaving lab write your percent germination and average root length values onthe chalk board.


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Post lab Questions:

1) Graph the percent germination class data using a program like Excel or usinggraph 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 theclass averages.

EXAMPLES !

2) Compare the results for each of the biofuels examined in your lab section. Basedon the data, which fuel seems to be the most toxic to seeds? Do the fuels effectboth germination and root growth in the same fashion?

3) Express the percentage solution values in units of molarity (mol/L). Compare themolarity 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 ofwhich fuel is most toxic? Why? Suggest additional experiments to support yourconclusions.

4) Look up the LD 50 values for each of these fuels, how do the LD 50 values compareto 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 inthe species tested. In other words, the toxicity of biodiesel is insignificant.(Remember that LD 50 values are a measure of animal, not plant toxicity!)


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BibliographyThis 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: Measuringecotoxicity using a lettuce seed assay" Department of Chemistry Gordon College.GEMS database 2010.

Background reading for the LD 50 values can be found in the following sources.2) Timbrell, J. Introduction to Toxicology, CRC Press: New York, 2002.3) Girard, J. Principles of Environmental Chemistry 2 nd ed., Jones and Bartlett Press:

Boston Mass. 2010, Chapter 16.


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Synthesis of Biodiesel

Chem Connections:The diesel engine was first designed by Rudolf Diesel in 1895. The original diesel

engines had two key design features. First they used heaver fuels, in other words, fuelswith 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 12-18 carbon atoms. Rudolf Diesel envisioned running hisdiesel engine with vegetable oil, which contains three chains that are 16-18 carbons long(See Figure 1: octane, soybean oil, and petroleum diesel, biodiesel). His design became areality in 1900, when the first diesel engines where produced and used peanut oil as a fuelsource.

The second distinguishing feature of a diesel engine is that the fuel ignites withoutusing a spark system. Compression of air before injection of the fuel creates heat, whichignites 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 enginesdesigned 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 fromoil which has already been used for cooking. This means that the 1-3 billion gallons offrying oil used in the US every year could be used to power vehicles instead of ending upin land fills or sewers!

Figure 1: Primary Components in Common Fuels. The fuels currently used incombustion engines are all complex mixtures. The primary component of each fuel isshown above.

O

O

CH2

CH CHCH2

CH CHCH2

CH37 4

H 3 C

Methyl linoleate (in biodiesel)

H 2 C

HC

H 2 CO

OO

OO

O

CH 2 CH CHCH 2 CH CHCH 2 CH 37 4



Glyceryl trilinoleate (in soybean oil)

Dimethyldecadiene (in diesel)

H 3 CC

H 3 C

HC

CH 2

HC

CH

H 2C H

C

H 3 C

H 2C

CH 3

H 3 C

CH 3 C

CH 3

CH 2

CH

CH 3

CH 3

Isooctane (in gasoline)


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This experiment will give you the opportunity to make some biodiesel starting fromvegetable oil. If you trust your chemistry skills you could even put your product from thislab into any diesel car. During the next experiment you will get to see how this fuelburns.

New Chemistry In order to make biodiesel from naturally occurring oils the long chainhydrocarbons must be chemically separated. This can be accomplished through a processcalled hydrolysis . In your body this is the first step in the digestion of fats and oils in ourdiet.

H 2 C

HC

H 2 CO

OO

OO

O

CH 2 CH CHCH 2 CH CHCH 2 CH 3



7 4

7 4

7 4+ 3 H 2O

HO

O


+

3

HOCH 2

CH

OH

CH 2

OH

Fatty Acid (linoleic acid)

Glycerol

Figure 2: This process of breaking down oil into fatty acids and glycerol (also knownas glycerin) proceeds very slowly without the addition of catalysts.

Notice that the reaction in figure 2 is balanced. By adding water the bonds betweenthe fatty acid chains and the glycerol have been broken. This process proceeds veryslowly without the addition of a catalyst. However, the hydrolysis reaction can becatalyzed by the addition of either an acid or a base (this is one of the reasons yourstomach is an acidic environment). The product of the hydrolysis reaction is a carboxylicacid, 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, methanolis used along with NaOH, which is a strong base that will act to catalyze the reaction. Nowater is used and the desired product of the reaction belongs to a class of chemicalscalled esters. Esters are like carboxylic acids, but instead of having the form RCOOH,esters are terminated with a carbon chain RCOOR. Notice that esters were present in theoriginal soybean oil. Since we changed one ester into another ester, this reaction is calleda transesterification . What physical properties would change when the soybean oil ischanged to three separate esters?

H 2 C

HC

H 2 CO

OO

OO

O



CH 2 CH CHCH 2 CH CHCH 2 CH 3H 3 C OH

NaOH

HOCH 2

CH

OH

CH 2

OH

H 3 CO

O


+

7 4

7 4

7 4

7 4

+

3

biodiesel (methyl linoleate)

Glycerol

3

Figure 3: The process we will use to produce biodiesel from soybean oil.


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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 separatedfrom the biodiesel. This is relatively easy because the two chemicals are immiscible (theydo not mix) and they have significantly different densities. Biodiesel has a density of0.884 g/mL and glycerol has a density of 1.261 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 thisexperiment.

Chemical mp ( oC) bp ( oC)or smoke

point

density(g/mL)at 25C

MolecularWeight(g/mol)

Hazards

soybean oil -21 241 0.894 879.4

methanol

sodium hydroxide

methyl linoleate(biodiesel) -35 373 0.884 294.5

glycerol

water

2) If you have 10.0 kg of oil that you want to turn into biodiesel, how many liters ofmethanol will you need? Use the balanced equation in Figure 3 and the molecularweight for soybean oil to complete the calculation.


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Experimental Procedures Today you will be making biodiesel and you will be collecting data from the seedgermination experiment. the class will start by running the biodiesel reaction, while theother gets starting collecting germination data. Then you will switch.

The ProblemProduce biodiesel from soybean oil, and compare the properties of biodiesel to otherfuels.

The ApproachWork in groups of 2 or three to synthesize the biodiesel.

Equipment needed:250 mL Erlenmeyer flask50 mL Beaker100 mL BeakerGraduated CylinderMagnetic stir barHeating and Stirring PlateThermometer (-20 100 oC)Parafilm to cover the 50 mL beaker while being stored

Chemicals Needed:0.4 M solution of NaOH in methanolSoybean or other vegetable oil

Day 11. 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 and50oC 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 50o

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.


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6. Stop the stirring and pour the mixture into a 50 mL beaker. Allow the mixture tocool and then cover the beaker with parafilm. Label the beaker with your nameand 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 germinationexperiment started during the last lab period. Directions and tables for this datacollection can be found in the previous experiment!

Day 21. 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 oC while stirring for 20 min.Heating your sample will generate methanol vapors and other fumes, so thisMUST be done in the fume hood.

4. Measure the volume of your final isolated biodiesel. Record this value in yournotebook.


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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 afterheating to remove residual methanol. Calculate the actual yield of biodiesel basedon the amount of biodiesel before separation and heating.

Use this table to answer the following questions.

4) If you had four containers without labels one biodiesel, one veggie oil, one

petroleum diesel, one gasoline what experiments would you have to run todifferentiate them?

5) How would you expect the viscosity of fuel to affect its performance on a coldday (think about -20 oC in the winter in Minnesota)? Which of the fuels listed inthe table above would work best on a cold day?

Fuel mp ( oC) bp (oC)

or smoke point

density (g/mL)

at 25C

viscosity (mPa s)

at 25C

Soybean Oil -21 241 0.894 69

Biodiesel -35 373 0.884 6.4

Gasoline (isooctane) -60 121 0.735 1.2

Petroleum diesel -40 315 0.848 3.5


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BibliographyNumerous versions of this lab are available in the chemical education literature andcan be found online. Our development was informed by the versions listed below.

1. John E. Thompson, "Biodiesel Synthesis" Lane College 2006 GEMS database,

follow-up personal communication, 2010.2. Amy Cannon, "Green Chemistry in the Curriculum: Biodiesel Module" BeyondBenign and Fisher science education, downloaded 2010.

3. Ehren C. Bucholtz, Biodiesel Synthesis and Evaluation: An Organic ChemistryExperiment J. Chem. Ed. 2007 , 84, 296-298.


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Biodiesel Heat of Combustion andEnergy EfficiencyChem Connections:

The heat of combustion is the amount of heat energy released when a substance iscompletely burned. From a chemical perspective, burning is the complete oxidation of achemical. For example, a hydrocarbon is completely burned when all of the carbon atomshave be transferred to CO 2 and the hydrogen atoms have turned into H 2O. Consider arelatively simple case, the burning of methane (the primary component of natural gas).

C

H

H H

H

+ 2 O 2 CO 2 + 2 H 2O

Hf (kJ/mol) = -75 0 -394 -242 The amount of energy produced by this reaction can be calculated by summing the bondenergies of each of the products ( H f is the heat of formation in kJ/mol), and bysubtracting the sum of the H f for the reactants. (When you are looking these values upyou should always use the values assuming your products are in the gas phase.) The heatof combustion for this reaction is: -394 + 2(-242) (-75) = -803 kJ/mol. Remember thatthe negative sign indicates that this energy is given off, so this is an exothermic reactionthat 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 wantto consider the concept of efficiency from a chemical point of view. It was mentionedthat diesel engines are more efficient than gasoline engines. Rather, diesel enginesconvert heat energy to mechanical energy more efficiently than gasoline engines. Thisweek 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 alsomeasure the amount of heat using a technique called calorimetry. Calorimetry is a generalterm for a number of techniques used to measure heat. In todays lab we are going to usea 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 theheat produced to heat water. It takes 4.18 J of energy to raise 1 g of water 1 oC. Forexample, consider heating 200 g of water from 25 oC to 35 oC. This is a change of 10 oC.So to find the energy that this change took, we multiply (10 oC)(200 g)(4.18 J/g oC)=8,360 J or 8.4 KJ. If it took 0.3 g of fuel to heat the water, then we can determine the heatof combustion by dividing (8.4 KJ)/(0.3g)= 27.8 KJ/g. So, by measuring both thetemperature increase in the water and how much fuel is used, we can determine the heatof combustion.


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Prelab Questions

1) It was mentioned that diesel engines take advantage of the ideal gas law (PV=nRT) tocreate the conditions for combustion. Calculate the temperature inside a piston whichcompresses air at room temperature and pressure (298 K, 1 atm) with a volume ratioof V 1 /V 2 = 15/1. The final pressure in the piston is 30 atm. How hot is the air aftercompression?

2) For the fuels listed below, calculate the theoretical heats of combustion using the

Hcomb =

Hf, products -

H f, reactants . Assume that 1 mole of the fuel burns completely togive CO 2 and H 2O. Finally, convert this value to energy density (kJ/g) which is theunit we will be measuring in todays lab.

Fuel Formula

Heat ofCompustion(kJ/mol)

EnergyDensity(kJ/g) Fuel

H f (kJ/mol)

Isooctane C8H18 Gasoline -44.3Hydrogen H2 biodiesel -839.2

Ethanol C2H5OHSoybeanoil -4171.6

MythylLinoleate(biodiesel) C19H34O2

Soybean oil C57H100O6

3) Calculate the final temperature for 225 g of water, which starts at 20 oC, after 0.75

grams of biodiesel have to be burned to heat the water. Assume all of the energy goesto heating the water.


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Experimental Procedure

The ProblemDetermine the heat of combustion for biodiesel using ethanol as a standard to calibrateyour calorimetry apparatus.

The ApproachWork in groups of 2.

Equipment needed:Oil Lamp with a wickRing StandMetal container for water with wire to suspend from the ring stand

Thermometer (-20 100o

C)Access to an analytical balance

Chemicals Needed:Biodiesel (from last week)Ethanol

PREPARING BIODIESEL FOR COMBUSTION1) Complete the separation and purification of your biodiesel from last lab period.

Directions can be found in lab manual Synthesis of Biodiesel under theDAY 2 heading.

MEASURING HEAT TRASNFER2) Once 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 thewick is exposed to fuel along the entire length. (If the wick is not completelywhetted 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 theexact same amount of water in each measurement.

5) Suspend the metal can from the ring stand and measure the temperature of thewater. Record this temperature.

6) If the temperature is less than the temperature in the room, allow the water towarm to room temperature before starting your experiment.

7) Once the temperature of the water has equilibrated with the room, light the oillamp and make sure it is placed as close to the metal can as possible, so that thetip of the flame is slightly below the bottom of the can.

8) Monitor the change in temperature with your thermometer, while also gentlystirring the water to insure even heat distribution.


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9) Once the temperature of the water has raised about 10 oC, 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 averageyour data. Each time start with fresh water at room temperature. Also make sureyou 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

Fuelgramsburned

molesburned T initial Tfinal T

EtOHEtOHEtOHEtOHEtOHBiodieselBiodieselBiodieselBiodieselBiodiesel

The ethanol experiment will give us a sense of how much heat the calorimeter itselfwill absorbs from the burning flame. We can then use this data to calibrate ourcalorimetry based on ethanols heat of combustion.

The best way to determine the heat of combustion for a reaction is to use a bombcalorimeter, where all of the heat from the combustion reaction is trapped inside aclosed system. In this system the amount of heat absorbed by the calorimeter is givenby the equation:

qcal = C cal X T

Ccal is the heat capacity for the entire bomb calorimeter. And is expressed in the unitskJ/C. This value must be determined experimentally for the calorimeter and is basedon the amount of heat that both the water and the surroundings absorb. This will betrue for our calorimeter as well.

In order to calculate C cal for our soda can calorimeters we will use the known valuefor the combustion of ethanol. ( Hcomb, EtOH = -1278 kJ/mol EtOH) Since q cal is the


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amount of heat aborbed during the reaction it will have a positive value forexothermic reactions, and will be equal to q combustion.

qcal = -q combustion = C cal X T-qcombustion = Hcomb X (moles EtOH)

(

Hcomb X (moles EtOH))/

T = C cal

Calculate C cal for your calorimeter using the combustion data you gathered for fromthe burning of Ethanol.

Reaction C cal EtOH 1EtOH 2EtOH 3Average

Then use the q cal expression to calculate the Hcomb for the biodiesel that you madelast week.

Reaction Hcomb Biodiesel 1Biodiesel 2Biodiesel 3

Average

Postlab Questions

1) Compare the values you measured for biodiesel, to the predicted values youcalculated in the prelab. Do they match? If not explain, why they dont andsuggest ways that the experiment could be improved.

2) The heat of combustion for biodiesel is a measure of chemical energy. Explain therelationship between chemical energy and fuel efficiency. Does a higher heat ofcombustion for a fuel mean it is more efficient? Explain what contributes to fuelefficiency.


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BibliographyThis 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 BombCalorimetry" J. Chem. Ed. 83, 2006, 260-262.2) American Chemical Society, Chemistry in Context Laboratory Manual. 6 th ed.

McGraw-Hill Science, 2008. In particular a personal communication withJennifer Tripp, an editor for the newest version of these labs.


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Report for the biofuels unitIn 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 (1-2pages) should compare and contrast two or more of the fuels sources that you havestudied during the last 3 weeks. You should consider the sources, synthesis, healtheffects, and efficiency of the fuel sources in the paper. Finally, include a recommendationfor or against the use of one or more of the fuels you choose to discuss. Evaluation of thisreport will be based on your ability to discuss the biofuels using data you collected fromlab or found in other scientific references.

Recommended Reading:1) Howard Wolinsky, The Economics of Biofuels, European Molecular Biology

Organization Reports , 10, 551-553, doi:10.1038/embor.209.1212) Melinda Wenner, The next Generation of Biofuels, Scientific American, March

2009, 46-51. ( http://www.scientificamerican.com/article.cfm?id=the-next-

generation-of-biofuels )

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GreenChemistry Biofuels Unit

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