Organic Chemistry Lab 315 Spring, 2017 (Dr. Pant’s section)

DUE DATES Today Next Week Two Weeks At beginning of lab -- Melting Pt. Report At end of lab -- copy of laboratory notebook pages for today's experiment (do not turn in your pre-lab or in-class notes) Next Week Nothing is due. I will return M.pt. reports. Two Weeks Due at beginning of lab -- Recrystallization Report

Today You can look at your M.pt. notebook copy, but you need to return it to me today. (You have your own copy in your notebook.) Make a note of errors you made on your own notebook copy. Work a bit on the Purpose. Saying that the purpose of last week’s lab was to “take a melting point of a solid” does not quite capture the essence. Manual asked for several statements about observations – these were each noted as present or missing: comparison of knowns’ m.pt.s with Table values comment on mixed m.pt. of knowns possible identity of unknown mixed m.pt. of unknown and suspected known table of data

Today The quiz (and all future quizzes) are a maximum of 50 points. Notice that most of the quiz questions came directly from the assigned reading and video. There is an answer key on my desk that you can look at.

In Lab Today Selection of a Recrystallization solvent Recrystallization of a solid sample Solid compounds synthesized or used as reactants in the Organic laboratory usually need to be purified (recrystallized). Next week a melting point range will be measured to ascertain the purity of the isolated compound

An Ideal Recrystallization Solvent Should: dissolve all of the solid when the solvent is hot (boiling). dissolve none of the solid when the solvent is at room temperature. have different solubilities for the solid and the impurities. have a lower boiling point than the melting point of the solid. have a fairly low boiling point

Steps in Recrystallization Use an Erlenmeyer flask. (The picture shows a beaker.) Dissolve crude solid in minimum amount of hot solvent. This must be done with small volume increments, and fairly rapidly so the solvent does not cool or evaporate.

Steps in Recrystallization 2. Let solution cool to room temperature, so that crystal lattice reforms slowly and impurities are not trapped. (Still in an Erlenmeyer. Cover with a watch glass.) 3. Cool solution in an ice bath for further crystallization, ~ 15 min. The mixture must be a “filterable” slurry. If it is a solid-like mass, heat to boiling and add a bit more solvent.

Steps in Recrystallization 4. Vacuum filter the pure solid, leaving impurities dissolved in solution. Some of the desired substance will also remain dissolved (it’s impossible to achieve 100% recovery). Rinse the flask with a small amount of ice-cold solvent to transfer the last few bits of solid. Rinse the crystals in the filter with a small amount of ice-cold solvent. 5. Let the purified solid air dry on a watch glass to remove traces of solvent. Transfer to a beaker to dry and store until next week.

Notes Make sure the balance is displaying ±0.001g. Take your notebook with you to the balance and record mass. Use the same balance throughout the entire experiment (2 weeks). Use ~ 1 g of impure fluorene from jar at balance. Weigh plastic dish. Then add ~1 g of fluorene. Weigh dish + fluorene. See Mohrig and Manual for recrystallization steps. Use hot water in a large beaker as a hot bath for heating organic solvent and solution. Add boiling stones for smooth boiling. If you forget to add them in the beginning, NEVER add stones to a hot solution. Cool solution first. Get ice from the stock room to make an ice bath. Use the ice bath to cool solvents for washing crystals, and to cool solutions below room temperature.

Notes DO NOT start over without permission. Store product in pre-weighed plastic dish in drawer marked “Pant - Tuesday” DO NOT start over without permission. Let me know if you have a problem.

Notebook-keeping Part 1 Part 2 Clearly record approx.quantities, procedure, observations and results for determining the best solvent. Please space your writing in the notebook to make it readable! Part 2 Record quantities of all substances used in a clearly labeled Table that is easily found in the notebook.

Notebook-keeping Keep a running total of solvent added. Estimate quantity if solvent has evaporated during heating. Write your procedure as you do it. Please space your writing in the notebook to make it readable! When doing calculations, pay attention to significant figures.

End of lab clean-up