Today:
•Quiz Comments
•Practice for Melting Point Ranges andRecrystallization
•Introduction to Molecular Modeling
(Lab today is in SEGA lab Science249)
Melting point ranges for mixtures of compounds A and BPhase DiagramWhat is the mp. and mol% composition of the eutectic mixture?What is the mp. range of mixture X?
oC
oC
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
The following solubility data were collected beforerecrystallizing a sample of caffeine (C):
SolventSol. Of C at 20oSol of C in hot solvent
Waterslightly solublesoluble
Ethanolsolublesoluble
Acetonesolublesoluble
Benzeneslightly solublesoluble
Pet. Etherinsolubleinsoluble
1) Which single solvent(s) could you use forrecrystallization?
2) Suggest a mixed solvent pair that you could use instead.
Solubility Data for Caffeine
1.000g of caffeine completely dissolves in a minimum of
–45.0ml of water at 14oC
–5.5 ml of water at 80oC
–1.5 mL of boiling water
Assume that you are recrystallizing 2.000g of impurecaffeine.
After one recrystallization from 30.0 ml of water you endedup with 1.200 g of purified caffeine. How many grams ofcaffeine were left in the cooled water? (careful …)
If you reduced the volume of the mother liquor to 5 ml, howmany grams of caffeine would be left in solution in thecooled solution?
Molecular Modeling
Remember these:
Hybridization of C
Bond length, angle, dihedral angle; staggered andeclipsed conformations
Conformations of cyclohexane; axial , equatorialsubstituents
We’ll do MM Exps. 1, 2, 4, only
Next time:Distillation/GasChromatography (Exp.3)(Notebook preparation please…Preview/prestudy experiment)