A. Benzoic acid and 2-naphthol have the same melting point (121-122 degrees C).

Question

A. Benzoic acid and 2-naphthol have the same melting point (121-122 degrees C). An unknown compound has a melting point of 121-122 degrees C. Melting point of a mixture of pure benzoic acid and your unknown sample was 116-122 degrees C. Melting point of a mixture of 2-naphthol and your unknown sample was 110-116 degrees C. What is your unknown?

1) benzoic acid

2) 2-naphthol

3) a mixture of benzoic acid and 2 naphthol

4) either benzoic acid or 2-naphthol

5) neither benzoic acid nor 2-naphthol

B. Melting point...

1) of a pure substance is always very sharp

2) is a characterstic physical property of the substance

3) is the temp range at which the substance changes the state from liquid to sold

4) cannot be measured for compounds that melt below 0 degrees C

5) all of the above

Explanation / Answer

1.. ans is   3) a mixture of benzoic acid and 2 naphthol

the melting point of the benzoic acid should be depressed (go down) compared to the literature value if you were to add 2-naphthol because the sample you were testing would then be impure, even if that impurity does have a similar melting point. Also, the range over which the sample melts should get larger as well.

B. . Melting point

yes the melting point of pure substances is always being sharp

elting point, boiling point, density is a characterstic physical property of the substance

HENCE ANSWER

5) all of the above

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