Today was the first day back in lab. We started classes last week, but the “lab” was just the safety & orientation class, not a real experiment. Then Labor Day off, so today, Tuesday, was the first real lab. The theme was recrystallization and melting points, so I showed that clip “89% Pure Junk” from The French Connection. They used authentic 1971 lab equipment and even had a correct melting point for the heroin (discounting slightly for the 11% impurities…)
The lab is in two parts, a recrystallization (benzoin acid adulterated with iron oxide, copper sulfate, phenylacetic acid, and phenoxyacetic acid) and a melting-point mix-and-match where the students are given an unknown, which was whatever we had on the shelf with mp = 130-135, and have to find at least one person with the same substance and one person with a different substance, and prove it by mixed melting points. That’s a good “get-to-know-you” lab because they are forced to interact with peers.
And the recrystallization worked better than expected. The Fe2O3 gave a pink tint to the solid that required hot filtration, the copper sulfate showed how water-soluble impurities remain in solution, and the two organic contaminants knocked the melting point down by a good ten degrees. The purified benzoic acid was white, and right back at 122 where it belonged after 20-30 minutes in the drying oven.
You forget just how little technique people know at the beginning of the year. Three flasks boiled dry and two broke, one of which dumped choking vapors all over. Note: even though the solvent is only water, they have to do the recrystallization in the hood anyway! But I didn’t see any pink or blue product turned in and yields were roughly 50% which is not bad for a beginner.
Today, beginning to work on how to use ChemDoodle Web Tools in teaching. This may require more than the D2L web site can handle, so I may wind up adding pages about O-chem to test out.
The ultimate goal is to convert class notes into an E-book with interactive or at least multimedia figures.