Question

1. How would a mixture of naphthalene and benzophenone behave on a TLC plate with hexanes / acetone as the eluent? Compare the polarity of these two compounds.
2. Outline the most commonly used procedure for the purification of an impure solid material using the technique of recrystallization.
3. Why is acetone such a popular solvent? Point out one drawback in terms of safety consid­erations.
4. Your final product might be impure since you suspect decomposition might have occurred. When determining the melting point of your product, what are you looking for?
5. Why is it important to use a minimal amount of hot solvent during a recrystallization? What would happen if you used too much solvent while dissolving your solid?
6. Why is it important to cool the dissolved product/solvent mixture slowly during a recrystallization?
7. Discuss the melting point range characteristics of a pure and an impure sample.
8. An accurate melting point range can be obtained by heating the sample quickly just as well as if obtained by allowing the temperature to rise slowly. True or False? Explain.
9. What is the first indication of a sample melting in the melting point tube?
10. Suppose your sample melts before you are ready to record the melting point. Should you:

a) cool the capillary and re-determine the mp or

b) begin with a fresh sample?

Explain.

Answer 1

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