Distillation Theory and Gas Chromatography
PreLab Quiz #6
Prof. Edelbach Spring 11
Name: ______________________________
10 pts
1. Distillation is a technique in which liquids can be separated due to their differences in: a. polarity b. density c. refractive index d. boiling point
2. T or F, A mixture of pentane and hexane can be effectively separated by simple distillation ?
3. T or F, A mixture of pentane and hexane can be effectively separated by fractional distillation ?
4. If a compound boils at 100°C at 760 mmHg, its boiling point at 775 mmHg will be: a. lower b. higher c. the same d. cannot predict
5. In a distillation of a mixture of two components, the second compound to condense into the receiving flask will be: a. the one with the lower melting point b. the one with the higher melting point c. the one with the lower boiling point d. the one with the higher boiling point
You are given a solution that contains equal numbers of moles of liquid A (b.p. 80 o C) and liquid B
(b.p. 100 o C). You may assume this mixture behaves like an ideal solution.
6. At what temperature (in o C) is this solution most likely to begin to boil? a) 80 b) 85 c) 90 d) 95 e) 100
7. When the solution described above just begins to boil, the vapor above the solution will consist of a) pure A b) pure B c) a 50/50 mixture of A and B d) mostly A but with some B present e) mostly B but with some A present

You distill the mixture of liquids A and B using the method described in the lab manual and obtain three fractions. You take the first (lowest boiling) fraction and inject it in the gas chromatograph and obtain two peaks, one with a retention time of 40 seconds and one with a retention time of 60 seconds.
8. Which peak in your GC is due to compound B ? a) the peak with 40 second retention time b) the peak with 60 second retention time c) it is impossible to tell without additional information
9. Which peak in your GC should be larger (have the greater area)? a) the peak with 40 second retention time b) the peak with 60 second retention time c) it is impossible to tell without additional information
10. A student is running late in lab and decides to speed up the GC analysis by increasing the carrier gas flow rate of the GC. What effect will this have on the retention times? What problems (if any) could result from this?