Answer to Question 1Yes, the Rf of Compound A be different. 50 Hexanes50 ethyl acetate is a more polar sol
vent system than is 90 hexanes10 ethyl acetate. Therefore, the Rf of Compound A would
be greater because the compound will travel further up the plate
Answer to Question 2(a) Compound B is the more polar compound.
(b) At 10 and 20 min, the reaction is not complete. At 30 min, it is complete.
(c) The student should obtain a standard sample of Compound B and run it on the same TLC
plate as the reaction mixture.
Answer to Question 3Either too much compound was spotted or the sample is very impure. The student should
dilute the sample and re-run the TLC. If a streak is again obtained, the student's product is
impure.
Answer to Question 4Table 11.1 (p. 122) gives the expected eltuion order of organic compounds in TLC. Biphenyl, an
aromatic hydrocarbon, is the least polar of the three compounds and will travel the farthest on
a TLC plate. Benzoic acid, a carboxylic acid, is the most polar and will travel the least far of the
three compounds. Benzyl alcohol, an alcohol, will travel in the middle.
Answer to Question 5(a) very polar: paper
(b) very polar: paper
(c) less polar: TLC
Answer to Question 6A single spot on a TLC plate does not necessarily indicate that the mixture spotted contains
only one compound. Many compounds can have the same Rf value on a TLC plate. To verify
the purity of the sample, it should be run in more than one TLC system. Or, resort to other
methods of purity assessment, such as melting point determination or spectroscopy.