tially, however, student performance on the exercise since no lab lectures were given during the 197576 academic year. This question requires application of knowledge. Question
and therefore
Since all values of k are positive, it follows that
.
which means that K,, at T7is greater than K.,, at T 1Q.E.D. .
Below are pairs of organic compounds. Based on your experience and studv. decide which of the indicated method or methods are be; suited to achieve a good separation. Place the letter which corres~ondsto the method of separation in the blank provided. methanol and ethanol capric acid and salicylic acid ~henoland cmrie acid mesityl tetrafluoroborate and nheptad 5) n-heptanol and ethanol 61 alkaline sdution ofcapric acid and phenol 1) 2) 31 4)
gas chromatography b) simple distillation C) extraction of aaueous layer with benzene d) recrystallization from water e) steam distillation a)
Selected Data on Organic Compounds
Separation of O r g a n i c Compounds
Solubiiitv
Paul R. Loconto Dutchess Community College Poughkeepsie, New York 12601 One final exam exercise that I have found useful directly pertains to the various separation and purification techniques commonly studied by students in the first semester of an introductory course in organic chemistry. The exercise seems to be an accurate test af whether the student can choose the most suitable technique based on his or her knowledge of the theory behind each technique. The instructor normally provides lectures on the theory of these techniques during the course in addition to the laboratory modules which also provide theory as well as practice. Laboratory lectures in class during the 1977-78 academic year have increased substan-
396 1 Journal of Chemical Education
Camoaund
mp lDCl
methanol ethanol n-heptanol capric acid salicylic acid phenol rnesitvl tetrafluoroborate
-97 -115 34 31 159 41 20
bp l0C1
64.5 78.3 176 269 182
H.0
H,O'"
EIOH
V V S S S S V
V V S S V
V V V V V V S
v V
Answer 1) a ; 2) e
and d ; 3) d ;
4) e; 5) o
and b; 6 ) e
Benzene V V
v V V
v S
