Green Chemistry

Strategies

"There is sufficiency in the world for man's need but not for man's greed"

Mahatma Ghandi (1869 - 1948)

Now that one has a basic understanding of the problems in chemistry, what green chemistry is, and what knowledge students should have about chemistry and its practices, it is time to embark on a set of strategies to enable student understanding of both the historical perspective of chemistry as well as the current influx of the practice of green chemistry and the principles of green chemistry. The following is a set of strategies that can be used during a 4-6 week period dependant upon teaching style. It is designed for flexibility to encompass all aspects of green chemistry for a basic understanding through the application of knowledge of chemistry itself. The following strategies are laid out in a logical sequence to allow a thorough understanding of the principles of green chemistry. Following these strategies will be a section for student activities that should be utilized for the completion of this unit.

The following are the key ingredients to the unit to be discussed

1. History of chemistry and waste production
2. What is Green Chemistry
3. Stoichiometry and the atom economy
4. What can be done to change mind set and be part of a movement towards green chemistry

History of chemistry and waste production

The historical aspect of chemistry through the ages will help build the knowledge of a wasteful chemical industry even if it not readily perceived from the onset of the unit. This section can be used to have students begin work on an independent group project, this being one that requires little time used in the classroom other than allowing groups to meet for a few minutes at a time to recognize their individual progress. Meanwhile, classroom instruction time during the project phase can be used to teach the prerequisite knowledge through independent autonomous standards employed by each individual teacher. In order to perform this task, student groups for studying each area of history should be created. Students will design a 20 minute lesson for their individual time period, posters, and visual displays (PowerPoint, graphs, photos, video excerpts etc…), and a worksheet designed to focus on the main points of their time period. Students will then spend time instructing the class about these different time periods through proper chronology so as to emphasize the changes in chemistry throughout history. Students will emphasize the waste being produced during each time period. Through this emphasis on the waste being produced throughout the different time periods, students will be building a sense of knowledge of product vs. waste which will be helpful in understanding atom economy and the need for decreased waste by the chemical industry as they attempt to make and maintain a more sustainable system.

Once students have established a proper understanding of the changes through chemistry and its history, they will be introduced to stoichiometry and its function in balancing chemical equations. Students will conduct chemistry labs to determine what amount of substance is being put into the process and what amount they receive of the desired substance. Through this, they can determine a relationship to the Law of Conservation of Mass as they have an identical, or close to identical, mass after the reaction with their new products in which they had of reactants being added into the system. By developing more guidelines to certain labs stating they are only concerned with generating a specific substance, they will begin to see a relationship between desired product produced and the waste production that was also generated from the same process. The use of molecular models will further demonstrate through a hands-on approach the recombination of chemicals into a new substance as they become aware of how many molecules are being used, as opposed to those no longer needed. Using the principle of a mol, students will then be able to see the amount of atoms being discarded, and the actual mass ratio of the waste to the desired product. The use of original synthesis formulas such as ibuprofen and propene is a crucial stage for students to see how things are being made. This should be done through an in class analysis of looking at the varying stages of the production of these substances as a teacher-led activity. Students should not be aware of the newer processes being done to make the same substances; rather they should only determine that these processes generate a desired product with a certain amount of waste. As students learn about green chemistry and atom economy, they will understand how inefficient these processes are. Once students have had ample opportunity to perform these tasks they are ready to understand what green chemistry is, and the impact of green chemistry on the chemical industry.

What is Green Chemistry

Although all of the 12 principals of green chemistry should be taught in the class for a basic understanding the following, four main ideas will be emphasized the most through instruction of this unit. They are:

1. Prevent waste: Design chemical syntheses to prevent waste, leaving no waste to treat or clean up.
2. Design safer chemicals and products: Design chemical products to be fully effective, yet have little or no toxicity.
3. Design chemicals and products to degrade after use: Design chemical products to break down to innocuous substances after use so that they do not accumulate in the environment.
4. Minimize the potential for accidents: Design chemicals and their forms (solid, liquid, or gas) to minimize the potential for chemical accidents including explosions, fires, and releases to the environment. ¹⁷

Stoichiometry and Atom Economy

Students should be taught the principles behind stoichiometry and balancing equations. Students should be able to determine the molar mass of the atoms and also be able to further convert them to total atoms using Avogadro's number. Once this is understood, students can be taught about atom economy. Atom economy is an important principle of green chemistry and one that is easy for students in the middle grades to comprehend. Students should look at the photosynthesis equation which they should already be familiar with. Using this equation, they can be presented with the formula for the efficiency of the equation using the following:

[Amount of desired product (each individual atomic mass added) * 100] /

[Amount of reactants used in the equation (each individual atomic mass added)]

This gives the percent efficiency of the process. Knowing that we need all the products of photosynthesis (in so much that oxygen is reused by the animal kingdom), they should find that:

C ₆H _{1 2}O ₆ + 6 O ₂ = [(6x12)+(1x12)+(6 x 16)] + [6(2x16)] = 372 x 100 or 100%

6 CO ₂ + 6 H ₂O

[6(1x12) + 6(2x16)] + [6(2x1) + 6(1x16)] = 372

If, however, we are only trying to determine the efficiency of glucose production as that is what is beneficial to the plants and the oxygen is actually waste, then we get

[(6x12)+(1x12)+(6 x 16)] / [6(1x12) + 6(2x16)] + [6(2x1) + 6(1x16)]

= 180 / 372 = 0.484 x100

= 48.4% efficiency

So the students would know that the waste was 51.6% of the process and not needed. Or for every 180 g of product there is 192 g of waste. Students should be able to recognize that a lot of waste formation can be found in this second set of equations as there is only one desired product from the process. Thus, there should be a different process that can capitalize on the production of the product (in this case oxygen) while accumulating less waste. Students should be presented with the task of coming up with ideas on how to get the oxygen more efficiently. After a discussion with leading questions towards finding new products that can be used to start the process that have less waste after the reaction, students can be presented with some real world examples of green chemistry in action.

Students should understand that the atom economy means that if there is less waste generated then there is more potential for greater profits by the chemical industry while also helping the environment by not adding more waste to it. When students understand this, it is time for them to revisit the production of propene and ibuprofen. Students should now conduct a discussion about how inefficient the processes are. Then they can be introduced to the current production means of both of these substances. This will give students a clear understanding of a chemical process that was done one way for many years without change, thus generating much waste, compared to the new approach being used today that produces less waste and is, therefore, more efficient by terms of atom economy. These two examples will generate the basic understanding of the principles of green chemistry. Dependant upon class structure and size there are many more examples that can be filtered in as extension and enrichment activities. See Appendix A for more resources.

Once students have become "experts" on green chemistry at their age-appropriate level, they will look at different objects they come into contact with on a daily basis and become student advocates for that particular object. Students will look at perhaps their shoes and determine what chemical process is needed to create that shoe. They will look more at a raw materials standpoint as to what is being used by certain companies to produce that shoe rather than the actual chemical make-up of all of the different parts, as that would be too high detail of an exploration for this age level. From there, they will research the possibilities of alternative materials for the shoe that will still give the same integrity to the shoe, or find other feedstocks that will have the right chemical combinations for the shoe to still be created the same way, but with less waste or less toxic release to the environment. From this knowledge, students will contact these companies' production departments, and specifically address to the VP of production for the facility. In their contact, they will lay out the concerns they have based on the waste products being generated currently and offer alternatives by providing knowledge of the 12 principles of green chemistry to the company. From this, the hope is to gain positive feedback from companies already exploring alternatives in production or will be doing so in the near future. The students may also send information to their state senator and suggest changes in importation of objects (such as tariffs) that do not follow protocols of green chemistry as a way of promoting growth of this science. This project will give students a sense of fulfillment in their understanding of this subject matter in that they will know that there are alternatives to creating the same or similar products. They will become more informed consumers in society and can help to fulfill the revolution of green chemistry in science. For a more detailed shoe example, explore Nike company's history and their new "considered" line of shoes that use water-based solvents, hemp for laces and tongues, and environmentally friendly inks and dyes. When students discover companies that have already made a transition, their project should focus on this positive characteristic. It can also be pointed out that the transportation of shoes from SE Asia still provide a negative impact on the environment, so although the manufacturing has gone green there is more that can be done.