These questions are in the5th edition of the Handbook for Organic Chemistry Lab. Once you've tried them on your own, click on the link at the bottom of the page to view the answers.
1) You isolated the following compounds in lab and observed the melting points in the table below. For each compound, look up the melting point in the Tables in the Handbook (or see the online Table of Physical Constants and Hazards of Some Organic and Inorganic Compounds) and judge the purity of the compound.
| compound | observed melting point |
|---|---|
| naphthalene | 79-80° |
| benzophenone | 45-47° |
| p-anisic acid | 178-182° |
| salicylic acid acetate | 135° |
| 3-chlorobenzoic acid | 157-158° |
| sulfanilamide | 165-166° |
| ferrocene | 157.5-161.5° |
2) You isolated lidocaine and novocaine in the laboratory. What are the melting points of these compounds? (They are not listed in the Tables in this Handbook. Hint: go to the Hazard and Physical Data for Compounds page.)
3) You think that you have isolated ibuprofen in the lab. Since you don't totally trust your own laboratory techniques, you want to prove to yourself that you have ibuprofen before you ingest it. Using only melting point techniques, explain how you can prove that you actually have ibuprofen. (Assume the stockroom is able to supply you with any compound you need.)
4) The melting point of a pure compound is known to be 110-111°. Describe the melting behavior expected if this compound is contaminated with 5% of an impurity.
5) You melt and observe decolorization, but miss the melting point. Should you cool the sample and re-melt it, or start over?
6) You melt a compound and it disappears: what should you do?
7) What setting should you use on the Fisher-Johns melting point apparatus to determine the melting point of:
8) What setting should you use on the Mel-Temp melting point apparatus to determine the melting point of:
9) You and your lab partner take melting points of the same sample. You observe a melting point of 101-107°C, while your partner observes a value of 110-112°C. Explain how you can get two different values with exactly the same sample.
