1. Today: Quiz Comments Practice for Melting Point Ranges and Recrystallization Introduction to Molecular Modeling (Lab today is in SEGA lab Science249)

2. Melting point ranges for mixtures of compounds A and B Phase Diagram What is the mp. and mol% composition of the eutectic mixture? What is the mp. range of mixture X? oCoC oCoC Pure A Pure B Solid A and B 100%A 50%A 50%B 100%B 75%A 25%B 25%A 75%B mol%A mol%B X E 20 140 80 40 60 20 60 100

3. The following solubility data were collected before recrystallizing a sample of caffeine (C): SolventSol. Of C at 20 o Sol of C in hot solvent Waterslightly solublesoluble Ethanolsolublesoluble Acetonesolublesoluble Benzeneslightly solublesoluble Pet. Etherinsolubleinsoluble 1) Which single solvent(s) could you use for recrystallization? 2) Suggest a mixed solvent pair that you could use instead.

4. Solubility Data for Caffeine 1.000g of caffeine completely dissolves in a minimum of –45.0ml of water at 14 o C –5.5 ml of water at 80 o C –1.5 mL of boiling water Assume that you are recrystallizing 2.000g of impure caffeine. After one recrystallization from 30.0 ml of water you ended up with 1.200 g of purified caffeine. How many grams of caffeine were left in the cooled water? (careful …) If you reduced the volume of the mother liquor to 5 ml, how many grams of caffeine would be left in solution in the cooled solution?

5. Molecular Modeling Remember these: Hybridization of C Bond length, angle, dihedral angle; staggered and eclipsed conformations Conformations of cyclohexane; axial, equatorial substituents We’ll do MM Exps. 1, 2, 4, only

6. Next time: Distillation/Gas Chromatography (Exp.3) (Notebook preparation please… Preview/prestudy experiment)