Growing your green chemistry mindset

1 Introduction

Becoming a greener chemist is a process which involves changing one’s attitude as well as an open mindedness. It is no longer acceptable to say, “I’ve been using this chemical for years and the amount of waste I produce is insignificant” when there is a better alternative. Developing a green chemistry growth mindset (GCGM) takes work [1]. The process involves rethinking demonstrations and laboratories for greener alternatives. There has to be a change in attitude in order to develop the GCGM. Operating out of older paradigms, such as “I am too busy to deal with GCGM,” will not lead to a significant improvement. At the same time, being overly concerned and mired down in detail may lead to the inability to execute and promote our wonderful field of study (yes, chemistry). This end of the continuum is the equivalent to saying, “I can’t improve, since I am too busy reading five books on self-improvement concurrently.” Green chemistry is a very healthy, balanced process that leads to a more sustainable future. We will look here at three principles of green chemistry and see how they can be integrated into the high school class or laboratory. While not formal case studies, these three examples provide several spots in a traditional curriculum where a green chemical principle can be inserted without any major change in focus for the course.

2 Principle #5 Safer Solvents & Auxiliaries

“Principle #5: Designing Safer Chemicals: Minimize toxicity directly by molecular design. Predict and evaluate aspects such as physical properties, toxicity, and environmental fate throughout the design process.”

Let’s take a look at one of the principles of green chemistry, #5, Safer Solvents & Auxiliaries. The dry cleaning industry used perchloroethylene (PCE) for a number of years. The use of this solvent peaked in 1980 [2]. Many people in the business knew that a better alternative was necessary, but the GCGM was not in vogue at that time. Having spent time in my father’s dry cleaners, my gut level intuition led me to believe that breathing PCE commonly called “perc” was probably not the best thing for my health. As time went on, my gut level intuition was supported, since the Environmental Protection Agency stepped in and suggested in 1990 that emissions of PCE be limited from dry cleaning plants [2].

Another relatively unknown fact is that Freon 113 (1,2,2-trichlorotrifluoroethane) was used as a solvent in dry cleaning until the Montreal Protocol prohibited its use due to its impact on the ozone in the stratosphere. Freon 113 was also used as a refrigerant, and very few people thought about ozone depletion when they were recharging their air conditioners. The GCGM requires one to look for alternatives (e.g. better solvents) before litigation occurs or before coercion by the EPA. This mindset is constantly asking: what is the better alternative compared to, it is still legal? Had a GCGM been in place perhaps Freon 113 and PCE would have been replaced sooner [2].

Another solvent used in dry cleaning is liquid CO₂, which must be under pressure, since dry ice (solid CO₂) changes directly from a solid to a gas at normal atmospheric pressure. This begs the question: when was the first commercial liquid carbon dioxide plant built in the United States? The answer is in 1999 in Wilmington, North Carolina [5]. This in turn begs the next question: would the first commercial liquid carbon dioxide plant have been built earlier if the GCGM was more prevalent at that time?

The intent of this discussion is to intimate or more realistically assert that being a green chemist is not a simple process. As soon as a chemist starts thinking about how to green a process, the GCGM has been initiated. However, like all great endeavours, the process is not always easy and at times may challenge what might be called one’s frustration tolerance level.

The following three examples provide students with the opportunity to segue into a discussion in a high school chemistry class.

1. Solvents. Water is the most common solvent that high school students will encounter. By providing real-life examples of other solvents and how they are used in industry, students are given the opportunity to compare and contrast which solvent is best when studying the solvent from a green chemistry perspective.

2. Phase changes and vapour pressure. The phase changes of CO₂ can be demonstrated by placing small pieces of dry ice into a plastic tube that can be closed as the dry ice sublimes into the gas phase, the students will witness the formation of liquid CO₂ as soon as the pressure is a little over 5 atm. This provides the students with the opportunity to see a liquid solvent other than water and a phase change that is less familiar (i.e. sublimation). The vapours associated with PCE and Freon 113 (e.g. vapour pressures) can also be part of a classroom discussion. Students will deepen their understanding of chemistry by researching and determining how green each material is.

3. Organic nomenclature and structure. Teaching nomenclature is a very important objective of the high school chemistry class. I personally think students should treat an introductory chemistry class as a foreign language class 10% of the time. Students should be given the opportunity to verbalize and discuss nomenclature. Freon 113 and “perc” serve as excellent examples of chemicals that have a systematic name and a common name. This discussion could conclude with the actions that these two chemicals have in the atmosphere, and their effect on the environment.

Though the discussion will be multifaceted as students discuss these three examples, in the end the goal is to direct the discussion back to green chemistry.

3 Principle #4 Designing safer chemicals

“Principle #4: Designing Safer Chemicals: Minimize toxicity directly by molecular design. Predict and evaluate aspects such as physical properties, toxicity, and environmental fate throughout the design process.”

This sounds like a thought process that an industrial chemist would use when designing a greener process. Extend this concept to the high school setting where the teacher deliberately chooses a demonstration based on whether the process is green. Once again, the focus will be on growing the GCGM. In this section, the teacher has decided to do an equilibrium demonstration. If the teacher chooses to use cobalt as indicated by the reaction below, then two questions arise. The first question most often asked is how to dispose of cobalt compounds. This question falls under the domain of environmental chemistry. One has created something that may pose a threat to the environment, what should be done at this point in time? The GCGM forces a teacher to consider whether the cobalt complex should be used in the first place. Though one may find this equilibrium expression intriguing or exceptionally interesting, the green chemistry question still remains: is this the best choice as an equilibrium demonstration? The teacher’s goal is to go through the green chemistry process, not directly answer the question for the students. If silver nitrate is added to the solution, then some silver chloride (AgCl) will precipitate out moving the equilibrium to the reactant side and the solution will be pink (assuming the starting solution is blue), as shown in the reaction. This is fascinating, since the silver chloride precipitate has formed and the equilibrium has shifted to the left. At this point, acetone can be added which will pull some of the water molecules towards the acetone which will lead to the solution turning blue in that region. This is a classic demonstration that has been used for decades. At this point in time, the question still remains: is this the best equilibrium expression to use to demonstrate the concept? The silver chloride precipitate can be filtered out, but this still leaves the green chemistry question unanswered. Is this equilibrium process green?

Though the chemistry involved in this equilibrium demonstration is extremely interesting, maybe it is best to use a video and limit the amount of waste produced on a yearly basis. This is a form of greening of the classroom that may be useful, but that should be noted to the students. Videos can enhance classroom learning and save time while greening the curriculum. Informational websites or videos should be incorporated into the curriculum when the teacher wants to green the curriculum, but not skip a great teaching opportunity [3, 4].

Let’s continue by examining a second equilibrium demonstration. In this demonstration, copper sulphate pentahydrate is dissolved in water forming a pale blue solution. At this point in time, this demonstration is not spectacular at all unless students are shown the copper sulphate pentahydrate crystals which are universally accepted as being “very cool” crystals based on their appearance (my bias was added intentionally). If concentrated ammonia is added to the solution, then the dark blue copper ammonia complex forms. To simplify the chemistry, this equilibrium expression has the water molecules removed. I highly suggest that this demonstration is done in a flat-bottom Florence flask. When concentrated HCl is added, a cloud of NH₄Cl solid is produced above the aqueous phase. This precipitate baffles students, since the ammonium chloride precipitate forms while the equilibrium shifts to the left. The removal of the ammonia (NH₃) occurs when the precipitate forms shifting the equilibrium to the left and a pale blue-coloured solution exists in the flat bottom Florence flask. Add additional concentrated ammonia and the dark blue copper ammonia complex Cu(NH₃)₄²⁺(aq)will form again as shown in the reaction, below.

The question in this case is: is this copper ammonia complex greener than the cobalt complex? Remember that the teaching goal is not to answer the question, but to model the thinking process to empower the development of the GCGM. GCGM may lead some to discuss the fumes from this demonstration, since breathing even small amounts of concentrated ammonia is not an enjoyable experience. Some may argue that using copper is greener than using cobalt.

These two equilibria reactions again provide examples of how green chemistry can be incorporated into the classroom. Examples include:

1. Is one particular equilibrium reaction greener than another?

2. Does the presence of a precipitate have any correlation to the “greenness” of a reaction?

Both questions can become sources of a larger discussion that include how one ion or another exists in solution, and if the use of one material is inherently safer than another, lessening the toxicity of the reaction.

4 Principle #12 Safer Chemistry for Accident Prevention

“Principle 12: Safer Chemistry for Accident Prevention: Choose and develop chemical procedures that are safer and inherently minimize the risk of accidents. Know the possible risks and assess them beforehand.”

Freon 113, as seen in Figure 1, as indicated earlier, had a negative impact on the ozone. Most cars used Freon 113 as a refrigerant until companies switched over to the new refrigerant. One can make the argument that the environmental mindset and the green mindset had very little to do with the switch. The change was motivated by economics. The new refrigerant was cheaper than Freon 113. If one had a GCGM back when people were changing which refrigerant that was used in their car, then an economic incentive might not have been needed.

Figure 1:

Images of Freon 113, 1,1,2-trichloro-1,2,2-trifluoroethane.

It doesn’t appear that many people are going to be concerned about what 1,1,2-trichloro-1,2,2-trifluoroethane (Freon 113) is doing to our stratosphere. Recalling from my personal observations at the time, many people interpreted the change in refrigerants as a nuisance and as unnecessary. Yet, this molecule is broken down to chlorine radicals which then break down ozone. Many students in a middle school or high school setting may find this information interesting as part of a classroom discussion.

If GCGM was part of mainstream thinking, then more people may ask whether basic chemicals are safer for the environment or not and inherently minimize risks. For example, ethylene glycol is used in the radiator of cars to lower the freezing point of the solution in the radiator. Yet, how many people are asking whether or not this is the best green alternative? One can imagine that by shifting our thinking in the green direction, we can impact a large segment of the society, at least beginning with students in high school chemistry classes. If a larger percentage of people ask for greener alternatives, then according to supply and demand economics more alternatives will be made available. Currently, many people are using ethylene glycol as a mixture with water in their coolant system. This may seem extreme, but using 100% water may be the greenest alternative in areas where the temperature never goes below 0°C (32°F).

Additionally, using a GCGM, can an argument be made that propylene glycol is a better alternative? Ethylene glycol shows up in forensic videos as a poison, and if it is accidentally spilled on a driveway, cats and dogs may consume a small amount due to the sweet taste (as a disclaimer: I have never taste tested this poison, but it appears to be well known that ethylene glycol has a sweet taste). If every teacher discussed the advantages of using propylene glycol as a coolant in the radiator of a car, then at the very least there would be a discussion of the toxicity difference between the two chemicals which could model the thinking involved in fostering the development of a GCGM. If it can be assumed that some people will spill some chemical when they are adding antifreeze to their radiator, then some number of people may choose to use propylene glycol. Principle number 12: Safer Chemistry for Accident Prevention, will be supported if more people choose a safer coolant for their radiator. The GCGM will create more discussion and if more teachers are given training in this area, then each individual student will have heard about it from their teachers.

Once again, this topic becomes one that can easily be incorporated into the classroom. Students are usually quite familiar with automobiles, and some students are fascinated by NASCAR and drag racing, so by bringing examples of automotive chemistry into the lecture or the laboratory student interest can be piqued.

5 Conclusions

At this point in time, it is imperative that teachers (K-16) start discussing these concepts with their students. The first step is for the teacher to develop a GCGM. The principles that we have studied involve predicting and evaluating the process before implementation. This requires work, and it will not always be fun. Going back to the two equilibrium demonstrations, one hopes you are trying to weigh out the different possibilities between using “wet chemistry” versus video or which equilibrium demonstration should be chosen and why. If you have a rationale for what you are doing from a green chemistry perspective, then you have probably initiated the GCGM.

The GCGM is a process and one can become concerned that teachers will not be given the time or the opportunity to grow in this area, since most people cannot explain the difference between an environmental mindset and a green mindset. Delineating them may lead to an opening activity where students in class or an online forum debate the difference between an environmental mindset and a green mindset. From that starting point, adding examples to the class can be done without difficulty.