BioFuels: The Chemistry and Economics of Alternative Fuels

Ralph D'Ambrosio

Garden City High School, Nassau County

Summer Research Program for Science Teachers

August 2008

 

 

Course: AP Chemistry, Honors Chemistry, Science Research

 

Fundamental Goal: Create a single, full year, chemistry project by linking several topics in the curriculum which will be completed at various times during the school year.

 

Objectives:

Students will learn, understand, and appreciate the following concepts:

  Separate matter in different phases.

  Determine the density of a liquid.

  Calculate the heat of combustion of a liquid using a calorimeter(Thermodynamics)

  A real chemical reaction

  Reaction Stoichiometry

  Identify and draw single, double, and triple covalent bonds.

  Learn the process of bonding.

  Inter-molecular forces of attraction

  Organic Chemistry Synthesis

  Environmental Chemistry

  Chemistry as related to the Economy

  Kinetics and catalysis

 

Materials, Apparatus, Chemicals:

Separatory Funnels

Round Bottom flasks and condensers (See Figure 1.)

TLC Plates

Thermometers

Metal Calorimeters (Coffee and soda cans)

Methanol, ethanol, vegetable oil, motor oil

NaCl

NaOH

Peanut oil( any vegetable oil will work fine also)

Silver Nitrate

Laboratory Notebook

Biodiesel (This will be synthesized)

 

Procedure:

1)      Making the Biodiesel: Lesson #1

(This Section is intended For Research or AP CHEMISTRY STUDENTS)

a) Have several students work in groups of three and set up the following apparatus. (an alternate suggestion is to have the teacher do this part)

Figure 1

b)      Based on the chemical reaction in Figure 2, have students determine the Stoichiometry for this reaction. (8:1 mole ratio of peanut oil to methanol)

c)      Add enough NaOH (catalyst) so that it is about 1% of the mass of the peanut oil used.

d)      Stir the mixture for about one hour at 600C. Remove the glycerol from the bottom of the flask with a pipet.

e)      The mixture is allowed to react for another 30 minutes.

f)       The product mixture is then transferred to a separatory funnel and washed with water until the pH is neutral. This ensures that the catalyst is removed from the reaction.

g)      Allow the reaction mixture to stand for 5 days.

h)     The reaction mixture is rewashed with NaCl(aq) saturated.

i)         Wash with AgNO3(aq)

j)        Remove the biodiesel layer from the aqueous layer.

k)      Determine its density.

2)      Thin Layer Chromatography: Lesson #2

 a)      Have students work in pairs and use TLC to check the purity of the biodiesel.

b)      Determine the Rf values of any spots and record their value.

c)      The eluting solvent can be a 2:1 mixture of hexane ethyl acetate or you can have students determine this.

 

 

3)      Heat of Combustion: Lesson #3

a)      Using a bomb calorimeter, If you are so blessed by the people who love to give grant money determine the heat of combustion of the biodiesel.

b)   If you live in the real world as I do, simply make a coffee can/soda can calorimeter.

 

(The calorimeter shown above might be similar to one that you use to measure the Joule content in a nut or other food.)

The only difference is to replace the tip shown under the calorimeter with some cotton rope.

a)   Determine the mass of the rope

b)      Soak the tip of the rope in the biodiesel and record this mass.

c)      Determine the mass of the soda can.

d)      Pour exactly 100.00ml of water into the smaller soda can and record the initial temperature of the water.

e)      Ignite the biodiesel as shown above.

f)      Continuously stir the water with the thermometer until the biodiesel is burned off the rope.

g)       Record the mass of the rope.

h)      Record the final temperatures of the water.

i)     Repeat a-h for each of the remaining fuels. 

j)        Determine the heat of combustion in Joules/gram of fuel.

 

Calculations

 

             Calculate the heat of combustion by using the principle of energy conservation.

Heat Lost by the Fuel= Heat Gained by the Aluminum can and the Water

                                    mcΔTfuel = mcΔTH20 + mcΔTAl

 

The individual lessons from this project can be as long term and at any level the instructor desires. The questions below can be used or revised to fit you r particular group of students.

 

Analysis Questions

 1)      Explain in terms if intermolecular forces why the layers separate in the separatory funnel. What IMFs are involved here?

2)      How and why did you determine the density of the biodiesel

3)      What do the Rf values from the TLC plates tell you?

4)      Determine the Entropy and ΔG values for this reaction.

5)      Using standard bond energies determine the heat of combustion of the biodiesel. How does this compare with your experimental value?

6)      In terms of bonds breaking and making, how is energy released in this reaction?

7)      Which fuel burned the cleanest? Why?

8)      How will biofuels affect the big picture of our Environment?

9)      Which fuel is the most economical?

10)  How will the use of each of these fuels affect our economy? Base your answer on information you have found in reputable journals.

11)   Why is the biodiesel washed in AgNO3?

12)   From known heats of combustion determine a % error

13)  If your value is high or low be concise and explain Why.

           

Bomb Calorimeter (If Dreams Come True)

Best Method for Measuring Combustion

 

 

National Science Standards

 Inquiry Standard

  Making clear and concise conclusions on the data they accumulate.

  Determination if they have taken enough data to draw conclusions about the environment and about the economic plausibility.

Physical Science Standard

  Precipitation Reactions

  Organic Chemistry

  Inter- molecular forces

  Bonding

  Thermodynamics

  Chemical Reactions

  Separation of matter

 Science and Technology Standard

  Use of computers to store data, and calculate necessary values.

  Use of computer interfaced temperature probes to take temperatures of combustion.

 Science in Personal and Social Perspective Standards