MELTING POINTS
READING
Zubrick, Ch. 1, 2, 3, 6, 9, and 12 (through “Operation of the Mel-Temp apparatus”)
Instrument Handout Using the Mel-Temp
PROCEDURE
A. Identification of an Unknown by Melting Points
Your instructor will provide you with a vial that contains a
compound from the list at right. Obtain a rough melting
point range of the sample, and then repeat to obtain an
accurate melting point range. From these ranges, identify
the compound.
You should report both rough and accurate melting
point ranges in your notebook. Your instructor will check
your accurate melting point range and may ask that you
repeat the test if not satisfactory.
Compound
Melting Point (°C)
Benzophenone
48
2-Naphthaldehyde
60
Benzhydrol
68
Vanillin
80
Benzil
95
ortho-Toluic acid
104
4-Hydroxyacetophenone
109
4-Hydroxybenzaldehyde
115
Benzoic acid
122
3-Nitrobenzoic acid
140
2-Nitrobenzoic acid
146
Adipic acid
153
Camphor
178
para-Anisic acid
184
B. Trends in Melting Points of Mixtures
Obtain accurate melting point ranges for three samples: pure urea, pure trans-cinnamic acid, and a mixture of
the two. (Mixtures are pre-made and will be assigned to you.) For each melting point range, calculate the
midpoint. (We are calculating the midpoint only for ease of graphing.) Post these ranges and midpoints on the
board in the lab or in an Excel file that your instructor has created.
Graph midpoint (y-axis) versus % urea (from 0-100, on the x-axis) for each sample. Comment on the trend
illustrated by the graph. Based on the graph, in what two ways are melting points for mixtures different from
those of pure compounds?
C. Identifying an Unknown by Melting Points
Your instructor will provide you with a vial that is either urea or trans-cinnamic acid. Obtain three
melting point ranges: the pure unknown, a mixture made from a small sample of the unknown and an
equal-sized amount of known trans-cinnamic acid, and a mixture made as above between the unknown
and known urea. Based on your data, identity of the unknown and explain how your data allowed
you to make this conclusion.
Organic Chemistry Lab Manual
Harper College, Fall 2010