An unknown compound melted at 131-133°C. It is thought to be one of the following compounds(mp,°C): trans-cinnamic acid (133-134); benzamide(128-130); DL-malic acid(131-133); or benzoin(135-137). The mixture melting points of the unknown compound with each of the test compounds are listed below. What is the unknown compound? Briefly explain your reasoning.

Question

-trans-cinnamic acid...........110-120
-benzamide.....................130-132
-DL-malic acid..................114-124
-benzoin.........................108-116

Answer 1

With mixed melting points you look for the following two criteria:
1. A sharp melting point (for example 110-120 is not anywhere near what I would call sharp)
2. A melting point that is VERY close to the unmixed unknown.

Answer 2

benzamide