______________________________________________________________________________
NAME
SECTION
DATE
EXPERIMENT
1 Report
Melting Point Determinations;
Determination of a Solid Unknown
Results
1. Individual Results.
Compound
Mp Range (C)
Midpoint of Range (C)
Literature Mp (C)
Urea
Cinnamic Acid
1:1 Urea/Cinnamic Acid
n/a
Assigned Urea/Cinnamic Acid Mixture
Assigned ratio = ______________
Unknown # ________
(approximate)
Unknown # ________
n/a
n/a
n/a
(careful)
Unknown mixed with _________________
Unknown mixed with _________________
Unknown mixed with _________________
2. Class Results for Part 3.
Prepare a graph that shows the midpoint of the melting point range versus the
composition of a urea/cinnamic acid mixture. Hint: for the X axis you can just label it "percent
urea in mixture" and go from 0 to 100%. (The percentage of urea in the mixture defines the
percentage of both components, since they are the only substances present.) Use your own
data for 0%, 50%, and 100 % urea. The graph should be done using spreadsheet software on
a computer. If this is impossible then you may prepare the graph on high quality graph paper
neatly in ink for a 3-point penalty. Make sure the graph is completely labeled and titled.
Conclusions (write up on a separate sheet of paper)
1. Part 2. What can you say based on your results about the melting point range of a pure
substance?
2. Part 3. What can you say based on the class results about the melting point of impure
mixtures of compounds?
3. Part 4. What is the identity of the unknown you tested? Explain your reasoning and provide
all pertinent information (unknown #, mp and mixture mp results, and literature mp) as part of
your answer.
Questions (write up on a separate sheet of paper)
1. Define the terms "melting point" and "melting point range", explaining completely any
differences in meaning between them.
2. Why is it important in determining a melting point to (a) pack the sample tightly in the
capillary tube, (b) heat the sample slowly as the melting point is approached, (c) use a small
sample in the capillary tube, and (d) use a finely ground sample.
3. A vial contains an unknown white crystalline solid. Describe an easy way to determine
whether the solid is a pure compound.
4. Three vials contain white solids X, Y, and Z, each of which melts at 119-121C. A 1:1 mixture
of X and Y melts at 100-107C. A 1:1 mixture of X and Z melts at 119-121C. In what range
would a mixture of Y and Z probably melt? What can you say about the identities of X, Y, and
Z?