1. Where is your nearest safety shower in the lab?
Near the whiteboard in the corridor area
2. Compound A melts at 101-102oC when pure, but a sample made in the lab was impure. What is the most reasonable of the following results for an impure sample?
(a) 101-105oC (b) 105-106oC
(c) 95-96oC (d) 95-98oC
3. Increasing the polarity of the mobile phase (eluent) for a TLC system will increase the Rfs for all of the materials spotted on the plate.
TRUE or FALSE
4. What was the purpose of the 2,2'-azobisisobutyronitrile (AIBN) in the free radical chlorination of 1-chlorobutane?
(a) A source of chlorine radicals
(b) A general source of free radicals (i.e. a radical initiator)
(c) A base to neutralize HCl and SO2
(d) A polar solvent for the reaction
5. In the separation of benzoic acid from benzophenone, what substance is present in the alkaline aqueous extract immediately before you add HCl for the first time?
Sodium benzoate (or you can draw the structure)
6. In the experiment where you prepared 1-bromobutane, the last step you did before running the IR spectrum was to add calcium chloride pellets to your crude product. The purpose of the calcium chloride was:
A drying agent
7. Which of the following is likely to be best for recrystallizing an alkane such as dodecane?
(a) water (b) toluene
(c) methanol (d) hexane
[Close in polarity, but not identical]
8. In the dehydration of 2-methyl-2-pentanol, the major purpose of heating the reaction mixture is:
(a) To speed up the reaction
(b) To suppress alkene formation, and instead favor the desired SN1 reaction
(c) To drive the equilibrium in favor of the product, by distilling out the product
(d) To decompose unreacted silver nitrate
9. In GC, retention time is used to
(a) Help identify which component is which
(b) Measure the amount of each component
(c) Measure the no. of hydrogens at each position in the product
(d) Measure the stability of each product
10. The O-H stretch in the IR spectrum of 1-butanol is seen at approximately:
(a) 660 cm-1 (b) 1220 cm-1 (c) 1680 cm-1 (d) 3500 cm-1
11. If a sample from a recrystallization is not fully dried, the melting point will be lower.
TRUE or FALSE
12. With a given eluent, the Rf of benzoic acid (C6H5COOH) is found to be 0.15. What is the most reasonable value for the Rf of benzaldehyde (C6H5CHO) using the same eluent?
(a) 0.05 (b) 0.15 (c) 0.30 (d) 1.50
13. (Worth more points) Briefly explain how a fractionating column works, to improve the separation when two similar B.P. liquids are being distilled.
In a fractionating column, there is a dynamic equilibrium set up between the liquid and vapor in the column. This allows the higher boiling fraction to recondense while the lower boiling fraction distils over. This makes it equivalent to doing many simple distillations at once, with the result that the components are more effectively separated. See the book for more detail.