CHEMISTRY I - LABORATORY EXERCISE
LABORATORY EXERCISE 10:
Melting Point and Boiling Point Determination
This is a traditional lab. You'll simply follow the
step-by-step procedure, keeping records of your measurements and
observations. Each student will write their own lab report,
which should include the following:
Names of lab partners:
Date of Experiment:
Date Report Submitted
Purpose: A brief statement about what the experiment is designed
to determine or demonstrate about chemistry
Procedure: Brief summary
Conclusions: What did you learn from the experiment?
Should be based on observations made during the experiment.
Evaluation of laboratory exercise type:
On a separate page, each student should write a brief comment
1) which lab method you prefer (inquiry-method, i.e.
problem-solving oriented, or traditional lab. like this one.
2) group size (individual labs or small-group labs)
3) report writing - individual or small group
4) Any negative aspects about chem lab & how we can improve
5) any other comments
We expect an evaluation from everyone. If you prefer not to put
your name on this evaluation, that's Ok.
1. To determine the boiling point of a liquid, and
2. To determine the melting point of a solid.
Isopropyl (Rubbing) Alcohol
1-2 small rubber bands
2 closed-end capillary tubes (melting point tubes)
10-12 mm diameter test tube
Discussion and Review:
In this experiment we will examine additional physical
properties of liquids and solids. Two of the more important
physical properties of pure substances are the boiling point
and the melting point.
The boiling point of a liquid is the temperature at which
that liquid is converted to a gaseous state. Boiling point is
formally defined as the temperature at which the vapor pressure
of the liquid becomes equal to the pressure at the surface of
the liquid. The boiling point of.a liquid can change if the
pressure at the liquid's surface changes. Since pure substances
have a distinct boiling point, boiling points are sometimes used
to determine the purity of substances.
The melting point is the temperature at which a solid is
converted to liquid. This is an important property of solids.
The melting point of solids, like the boiling point of liquids,
is often used for the identification of substances.
Boiling points and melting points are recorded in the Handbook
of Chemistry and Physics, and can be found in the sections
titled "Physical Constants of Organic Compounds" and "Physical
Constants of Inorganic Compounds".
I. Boiling Point
1. Make a test tube assembly by using the following directions
a. Place about 1 mL of Isopropyl alcohol in a 10-12 mm diameter
b. Using a small rubber band, attach a thermometer to the
outside of the test tube. The thermometer bulb should be even
with the test tube's bottom.
c. Insert an inverted closed end capillary tube into the
2. Make a water bath assembly by using the following directions
a. Half fill a 100 mL or larger beaker with warm tap water.
[Note: a water bath is used if the boiling point of the material
is expected to be less than the boiling point of water;
otherwise, an oil bath is needed.]
b. Place the above test tube assembly in the water bath so
that the surface level of the alcohol in the test tube is
beneath the surface level of the water bath.
c. Place the beaker on the wire stand and, stirring frequently
to insure even heating, carefully heat the water bath with your
heat source until the water bath boils and a rapid stream of
bubbles continuously emerges from the capillary tube.
[Note: if an oil bath is used, the oil does not boil; the
stream of bubbles from the capillary tube is the sole indicator
that the liquid in the pipet or test tube is boiling.]
d. Remove the heat source and begin observing the stream of
e. When the last bubble emerges from the capillary tube, record
3. Reheat the water bath and repeat the cooling process two
more times. Record the temperature reading after each trial,
and average all three trials.
4. The published boiling point of isopropyl alcohol is 82.4 oC.
5. Calculate the error between the observed boiling point and
the published value of the boiling point.
II. Melting Point
1. a. Push the open end of a capillary tube into the powdered
b. Move the powder to the closed end of the capillary tube by
tapping it on the table. Repeat until the the powdered acetamide
occupies 1-2 mm of the capillary tube end.
c. With rubber bands, attach the capillary tube to a
thermometer and align the bulb of the thermometer with the
closed end of the capillary tube.
d. Make a water bath as before by half filling a 100 mL beaker
with warm tap water.
e. Place the thermometer/capillary tube assembly in the water bath so that
the surface level of the powdered acetamide is beneath the
surface level of the water bath.
f. Place the beaker on the burner stand and, stirring
frequently to insure even heating, carefully heat the water
bath with your heat source.
g. Note the temperature at which the acetamide melts.
Remove heat source.
h. Let the acetamide cool and recrystallize.
Repeat the procedure two more times and average the results.
i. The published melting of acetamide is 81oC.
Compare your experimental result with the accepted (published)
j. Calculate the percent error.
Dispose of the used capillary tubes by putting them in your
trash can. If any isopropyl alcohol is left in your test tube,
you may pour it down the drain with water.
All contents copyrighted (c) 1998
Peter Jeschofnig, Ph.D., Professor of
Science, Colorado Mountain College
All Rights reserved
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