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Slide 2 / 25 Applying Green Chemistry to Purification The goals of this lab are to:

· Design a procedure to separate two substances using the principles of green chemistry. · Assess the quality of a lab report submitted for peer review before being published.

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What chemists do is design chemicals and chemical processes. These practices involve a few main principles. One of these is that pure substances have unique properties that can be used to distinguish them from one another. A second principle is that chemists consider the benefits and risks of different options when deciding which is the best chemical process. These two principles form the focus of this experiment.

Background Slide 4 / 25

1 List as many physical properties of matter you can think of that can be used to distinguish two substances from one another.

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The 12 priniciples of green chemistry are also considered in the purification of a mixture. 1. Create no waste. 2. Nothing should be left over. 3. No toxicity. 4. Green products have to work as well as nongreen products. 5. Get rid of all non essential additives. 6. Reduce energy usage. 7. Use renewable materials. 8. Get rid of as many steps as possible. 9. Make use of a reusable method to speed up a reaction. 10. Use materials that break down in the environment (biodegradable). 11. Check everything you do against the other principles. 12. Safety first.

Principles of Green Chemistry

Slide 6 / 25 Principles of Green Chemistry

Principle 2 is called the Atom Economy principle. The less is left over, the better. In the most ideal case, all of the starting materials are converted into the desired product and there is nothing left over. In order to compare processes in terms of how much is left over, atom economy is calculated.

Slide 7 / 25 Principles of Green Chemistry

Atom economy = mass of desired product (D) x 100 % mass of total product (T) When D/T = 100% then there is nothing left over because there is only one product, the desired one.

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2 If the atom economy of a reaction is less than 100% what does that say about the reaction?

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3 The following two reactions are possible methods for refining copper in the final step of a smelting process, i.e., getting pure copper (Cu) from copper ores found in rocks. Calculate the theoretical atom economy for each reaction. 2CuO (s) + C (s) 2Cu (s) + CO2 (g) CuO (s) + CO (g) Cu (s) + CO2 (g)

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4 Which method creates the least amount of waste? Which has the higher atom economy?

A Reaction 1 B Reaction 2

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5 Why is a calculation of atom economy helpful in comparing two chemical reactions to determine which one is greener? In other words, what does atom economy tell you about "greenness"?

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6 What is another possible consideration from principles of green chemistry that could tell you more about comparing the "greenness" of these two reactions?

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7 Peer review is a critical component of how scientists communicate what they have learned and contribute to new knowlege. What is peer review? Why do you think that scientists believe it is important for published work to be peer reviewed prior to publication?

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8 Why is peer review an important part of a process of chemists considering benefits and risks? Why might peer review be important in chemists reporting results of a chemical process?

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Materials: A mixture of sodium bicarbonate and sodium carbonate, scoopula, Bunsen burner (hot plate), ring stand, wire gauze, crucible and cover, balance, weighing paper, electronic scale, and tongs. Setup:

· Each group of up to 3 students is given access to or is given the materials listed above.

Slide 16 / 25 Guided Lab - Procedure and Examples Slide 17 / 25 Roles

Lab teams should consist of up to 3 students. The students should take turns and rotate through the roles listed below. As a team, the students will outline their procedure. 1. One person is responsible for massing the crucible and cover, and the crucible and cover and sample before the experiment begins and after each heating. 2. One person records the observations. 3. One person is responsible for collecting the mass data and leading the completion of the calculations.

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· Students will determine their procedure as to how many times and how long to heat the mixture.

Procedure

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· Do not heat covered crucibles. Always place the lid askew on top of the crucible while heating. Completely covering the crucible is dangerous because gases can build up inside while heating and hot lids can fly off. · Allow the crucible and cover dish and sample to cool for 5 minutes and then mass and record the mass to the nearest 0.01 g or better. · Consider as you complete the lab possible sources of error.

Special Considerations Slide 20 / 25

Safety Warning:

· Always place the lid askew on the top of the crucible while heating. · Use all due caution with the Bunsen burner or hot plate. · Hot things (like evaporating dishes and metal rings) look like cold things; do not touch anything with bare hands. · Students must pull back their hair to avoid a fire hazard. · Instructors should also familiarize students with the location of laboratory safety equipment. Students should know where to find running water, an eyewash and shower, an emergency blanket and the fire extinguisher before beginning the lab. · Tell the instructor of any accidents immediately. · Keep food and drinks out of the laboratory work area.

Slide 21 / 25 Data Collection

· Collect mass data on your crucible cover and sample after each heating.

Mass determinations should be made on items that have completely cooled.

· Make observations before, during and after heating your sample.

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Analysis and Application Questions

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9 A 4.218 g sample of a mixture of sodium bicarbonate and sodium carbonate is heated and has a final mass of 2.924 g. What is the relative mass of each of the substances in the mixture?

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10 Analysis of a sample of Chromium (III) nitrate hydrate finds that it is 40.50% water by mass. What is the chemical formula and name of this hydrate?

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