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Melting Point Technique Quiz

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 Chemical Information page) and judge the purity of the compound.

Compound Observed MP
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°

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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 Chemical Information page.)

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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.)

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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.

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5) You melt and observe decolorization, but miss the melting point. Should you cool the sample and re-melt it, or start over?

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6) You melt a compound and it disappears: what should you do?

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7) What setting should you use on the Fisher-Johns and Mel-Temp melting point apparatus to determine the melting points of acetylferrocene and p-anisic acid?

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8) 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.

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9) Which of the melting point capillaries in the picture below is filled to the proper level for taking a melting point on a MelTemp melting point apparatus?

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