Question

1. Consider the following pairs of compounds. For which pairs can simple distillation be used, and for which ones would fractional distillation be more suitable? (You will have to look up the boiling points.)

a. Hexyl acetate and butyl acetate

b. Hexanol and cyclopentanol

c. p-Xylene (1,4-dimethylbenzene) and benzene

2. Using the nomograph in your lab manual, estimate the following boiling points:

a. p-Xylene (bp 138 °C at 760 mm) at 150 mmHg

b. p-Xylene at 15 mmHg

c. Linoleic acid (230 °C at 16 mmHg) at atmospheric pressure

3. A mixture of compounds A and B was run on TLC using 10% ethyl acetate/90% hexanes, and the R f values of 0.05 and 0.12 were obtained. Is this optimal? How can the separation be improved?"

*no nomograph was provided*

Answer 1

1)

a) Hexyl acetate and butyl acetate: The boiling point of Hexyl acetate is 171.5 °C while the boiling point of butyl acetate is 126 °C. There is a huge difference between the boiling points of these compounds. Thus, these can easily be separated by simple distillation.

b) Hexanol and cyclopentanol: The boiling point of Hexanol is 157 °C while the boiling point of cyclopentanol is 140.4 °C. There is not much more difference between the boiling points of these compounds. So, these can be separated by fractional distillation.

c) p-Xylene (1,4-dimethylbenzene) and benzene: The boiling point of p-xylene is 138.4 °C while the boiling point of benzene is 80.1 °C. There is a huge difference between the boiling points of these compounds. So, these can easily be separated by simple distillation.