EXPERIMENT #1
Identification of a White Solid
The melting point of a compound is useful in establishing its identity and is a criterion of its
purity. By finishing Experiment #1, we will master the melting point determination technique to
identify a given unknown solid compound.
READING ASSIGNMENT:
Technique 14: Melting Points and Melting Ranges in Techniques in Organic Chemistry 3rd
Ed. pgs 174-183
Technique 5.4: Measuring Temperature in Techniques in Organic Chemistry 3rd Ed. pgs 4749.
PRELAB ASSIGNMENT:
Complete the melting point prelab assignment on Sapling Learning.
Safety Information
Wear gloves when handling the unknown compounds. Avoid all contact with skin, eyes,
and clothing.
Care must be taken while tapping the capillary tube against the bench top: it could break
and cause a cut.
If the heater on a Mel-Temp apparatus is not turned off after the measurement, the high
heat may ruin the thermocouple calibration.
Do not touch the heating block even after the light is turned off. You might get a serious
burn!!
EXPERIMENTAL NOTES:
A. Thermocouple Calibration
We will be calibrating our thermocouples (instead of thermometers) following the general
procedure described in Technique 5.4.
What You Need To Do Before Lab:
 Rewrite the procedure for calibration in your own words! (Use benzoic acid and
salicylic acid as reference compounds.)
 You will also need to refer to Technique 14.3 for details on preparing a melting point
sample and obtaining melting point data.
Data to Record
 Observed melting ranges of benzoic acid and salicylic acid.
 Plot a calibration curve based on your melting points (See Figure 5.12 for an example
of a calibration curve).
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B. Determine the Melting Point of an Unknown White Solid
Your TA will provide you with a sample of an unknown white solid. Determine the melting
range of your unknown compound following the general in Technique 14.3.
What You Need To Do Before Lab:
 Rewrite the procedure for determining a melting point in Technique 14.3 in your own
words!
Data to Record:
 Observed melting range of your unknown.
 Don’t forget to correct your observed melting points based on your calibration curve!
C. Mixed Melting Point of Urea and Cinnamic Acid
We will use the general procedure in Technique 14.5 to find the melting point of a mixture of
urea and cinnamic acid. We will also determine melting points for samples of pure urea and
cinnamic acid.
What You Need To Do Before Lab:
 Rewrite the procedure for determining a mixed melting point in Technique 14.5 in
your own words!
 Include the following in your procedure:
o To make the mixed sample, mix approximately equal amounts (~5 mg each)
of urea and cinnamic acid. Grind the mixture with a spatula. Make a sample
with this mixture and a capillary tube.
o Make samples of pure urea and pure cinnamic acid.
Data to Record:
 Melting ranges of all three samples.
D. Determine the Identity of Unknown.
Base on the melting point range of your unknown (determined in Part B), you will identify
your unknown by conducting mixed melting point experiments.
What to Do Before Lab:
 Based on the procedures you have already written, write a procedure for using the
mixture melting point technique that will allow you to determine the identity of your
unknown. (You won’t know which reference compounds you will need to use for
your mixed melting point experiments yet, but leave space to write those in.)
Data to Record:
 Reference compounds that have melting points close to the range you observed for
your unknown
 Melting ranges of any mixed samples you use to identify your unknown
 The identity of your unknown
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NOTES FOR WRITING YOUR DISCUSSION:
Your Theory section should include:
 An explanation of melting point on the molecular level
 A brief discussion of the factors that affect a compounds melting point
 A brief discussion of eutectic point
Your Results section should include:
 A calibration curve for you thermocouple
 A data table with the melting ranges of ALL the samples you ran
Your discussion section should include:
 A brief explanation of the calibration curve
 A brief explanation of the urea/cinnamic acid mixed melting point experiment
 An explanation of how you deduced the identity of your unknown.
Your Sources of Error/Future Experiments section should include:
 Evaluate any experimental difficulties you encountered and explain how they may
have affected your results.
 Discuss whether melting range determination is a sufficient technique for
determination of the identity and purity of a compound. Propose different
experiments/techniques that would address the issues of a compound’s identity and
purity.

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