Activities
Activity 1: Combustion of methane and isopropyl alcohol demonstrations
CH 4 + 2 O 2 —> CO 2 + 2 H 2O (equation 7)
Students will be able to visually see 2 combustion reactions. The first reaction is the combustion of methane gas (equation 7). This demonstration traps methane gas in a soap bubble and then ignites the bubble. The students will see a flame in mid air as the methane combusts and provides a clear visual for a combustion reaction.
In order to do this demonstration, easy access to a gas line is necessary. Most school gas lines use methane but teachers should double check before trying out this experiment. This demonstration requires three set ups. First, rubber tubing that is about 3 meters in length must be obtained. One end is connected to the gas line and the other end is attached to a plastic funnel. The second set up is a shallow bucket of soap and water mixture. To test out the soapy water, place the funnel's opening into the soapy water and a film should appear on the funnel's opening. The final set up is a long stick, such as a meter-long ruler, with a candle attached at the end.
Begin the demonstration by placing the opening of the funnel into the soapy water. Check to see that a soapy film covers the funnel opening. When the gas is turned on, the methane gas travels through the tubing into the funnel and makes a bubble filled with methane gas. Only a small amount of gas is needed or else the bubble will pop so practice is essential to get comfortable with this step. The bubble is carefully released from the funnel with the flick of the wrist. Because methane is less dense than air, the bubble will float to the ceiling. While the bubble is in the air, the lit candle is placed into the bubble, which will burst the bubble and ignites the methane gas. The students will see the combustion reaction occur in mid air (see Appendix B)
2 C 3H 7OH + 9 O 2 —> 6 CO 2 + 8 H 2O(equation 8)
The second demonstration involves the combustion of isopropyl alcohol in a 5-gallon plastic bottle (equation 8). This demonstration is appropriate after students have had practice balancing equations and are somewhat comfortable with stoichiometric calculations. Since the balancing of this equation is more complicated than the combustion of methane gas, it can be used as an opportunity for students to do some calculations. Before the actual demonstration, ask the students to balance the equation themselves and predict how much water should result from the combustion of a certain amount of isopropyl alcohol.
To execute this demonstration, 15 mL (approximately 11.80 grams) of isopropyl alcohol is poured into the 5-gallon plastic bottle. The bottle is then capped and rotated so that the alcohol coats the sides of the bottle. This is to make sure the alcohol vaporizes inside the bottle and is ready for combustion. If liquid is still left in the bottle, open the cap, discard the liquid, and recapped immediately. Weigh out the discarded liquid to calculate how much isopropyl alcohol remains in the bottle. The calculated mass will be used to determine the mass of water that should be produced from the reaction. The cap of the bottle is then opened and a lit candle attached to a meter stick is placed at the opening. When the alcohol is ignited, the students can see the combustion reaction in the bottle and water, a product of combustion reaction, will be left in the bottle afterwards. This demonstration will help students practice balancing equations and solve for the stoichiometric relationship between the mass of isopropyl alcohol burned and the mass of the water remaining. In addition, students can also calculate percent yield and discuss sources of error (See Appendix C).
Activity 2: Making biodiesel
The laboratory activity for this unit will be to make biodiesel from vegetable oil. Students will begin with vegetable oil and break the bonds of the triglyceride by using sodium methoxide. Once the biodiesel is made, students can compare it to the vegetable oil through a viscosity test to see the difference between the original vegetable oil and their final biodiesel product.
The actual procedure for making biodiesel from vegetable oil is simple but it is time consuming. Students should work in pairs for this lab if enough equipment is available. The lab will take two days to complete. On the first day, students will take vegetable oil and will make crude biodiesel through transesterification. To do this, students will measure out 14.0 mL of methanol and place the reagent in a jar with a lid. Next, they will measure out 0.50 grams of sodium hydroxide and add the sodium hydroxide into the jar with methanol. With the cap on, students will shake the jar to dissolve all the sodium hydroxide. This is an exothermic reaction so students should observe that the jar gets hot. Pressure will also build up so students should open the jar cap periodically to release the pressure. The resulting product from this reaction is sodium methoxide.
Next, students will obtain 60 mL of warm vegetable oil (around 50 oC). The warm vegetable oil is then slowly added to the sodium methoxide. After securing the lid once more, students will carefully but vigorously shake the mixture for at least 10 minutes. The jar should then be labeled and set aside for the next day for the glycerin and the biodiesel to separate out.
The following day, students should observe two layers in their jar. Glycerin will appear cloudy at the bottom of the jar and the biodiesel in the top layer should look light yellow and clear. The product formed is crude biodiesel that can be washed for further purification. This is done by pouring only the top biodiesel layer into a separatory funnel, adding distilled water to the crude biodiesel and shaking the mixture. The polarity of the water molecules will pull all the impurities out, leaving purer biodiesel. The washing of the crude biodiesel is best done as a demonstration as it can get messy and time consuming. Also, if a separatory funnel is not available, the washing step can be skipped.
A comparison of the viscosity of the product and original vegetable oil will help students determine if they have successfully created biodiesel. If drops of the biodiesel and vegetable oil are allowed to run down a slanted surface, the biodiesel should move along faster because it is less viscous than the vegetable oil. In the post lab, students will calculate percent yield using the volume of vegetable oil used and the volume of biodiesel that they made. Volume is used for percent yield instead of mass because gasoline stations use dollars/volume for their pricing. Then students will calculate how much vegetable oil is required to fill a 10-gallon tank car with biodiesel. See Appendix D for the biodiesel lab sheet.
Activity 3: Reading science articles and Report
A part of this unit is for students to calculate the energy released from high octane gasoline and biodiesel. Once students have calculated energy outputs they may wonder why there is a push for biodiesel when the energy output is less than high octane gasoline. At this time, students will be introduced to the idea of global climate change and the impact that high octane gasoline, made from fossil fuels, has on the environment. They will read articles taken from scientific sources that express different points of view. Some articles will argue that the world is running out of fossil fuels while others will claim that fossil fuel energy is plentiful. Some articles will support biodiesel production while others point out its downfalls.
After reading several articles and doing their own research on the internet, students will be asked to form their own opinion on what they think would be the best fuel for their community and support their opinions with facts from their own research. The students will write a persuasive essay based on the rubric in Appendix E.
Activity 4: Presentation
When the students are finished writing their essay and are able to confidently support their views, they will work with a partner to create a presentation on the best energy source for their community. The twist to this presentation is that each pair will be assigned a particular group with an interest in energy and the presentation will have to be from the viewpoint of that particular group. Some examples of these groups are oil companies, schools, college students, and environmentalists. The goal of the presentation is for students to recognize the complexity of this topic in that each interest group has their own perspective and there is no clear solution to this very important issue.
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