Post on 17-Oct-2014
International Program on Science Education
Laboratory Work in Chemistry
STUDENT WORKSHEET: SUBLIMATION OF IMPURE NAPHTHALENE
Nurul Aisyah
(1002561)
Bachelor in Education Candidate
February 2012
International Program on Science Education Department
Mathematics and Science Faculty
Indonesia University of Education
SUBLIMATION OF IMPURE NAPHTHALENE
I. Objective:
To purify organic solid compound
To practice the purifying technique for separating one component from its
mixture
II. Background
Sublimation is a purification technique, in which a solid is directly converted
to vapor phase without passing through liquid phase. However, the compound must
have a relatively high vapor pressure, and the impurities must have significantly
lower vapor pressures. By heating, the solid will be vaporized and become solid
again when the vapor contacts with the cold surface. Some solid compounds, such as
iodine, camphor, naphthalene, acetanilide, benzoic acid, can be purified by
sublimation at normal pressure. Several compounds will sublime when heating
under reduced pressure.
III. Chemical and Apparatus
Apparatus:
1. Beaker Glass 100ml 1pc
2. Mortar and Pestle 1pc
3. Watch Glass 1pc
4. Evaporation cup/ porcelain cup 1pc
5. Bunsen burner 1pc
6. Tripod 1pc
7. Digital balance 1pc
8. Road Stirrer 1pc
9. Ice 5pc
Chemical:
1. Naphthalene 2gr
2. Sands 1gr
III. Procedure
1. Mash 2 grams of naphthalene using mortar and pestle.
2. Place 2 grams of impure naphthalene (mixed with a minute amount of sand) in
beaker glass.
3. Stir the mixture of naphthalene and sand using stirring rod.
4. Heat impure naphthalene on an opened flame (do not forget to use tripod and
wire gauze)
5. Close the top of the beaker glass by using watch glass that consist of two cub of
ices on the top
6. Heat until the changes happen in the watch glass, observe it.
7. Turn off the flame, let the mixture cools down
Ps: Avoid breathing in naphthalene vapor.
IV. Result and Discussion
Analysis of impure naphthalene
Changes that occur during heating (in
beaker glass)
There was fog inside the beaker glass
indicated that the naphthalene began
to sublimated
Changes that occur during heating (in
watch glass)
The ice melted while there were
crystals begun to be formed on part of
watch glass inside the beaker glass
Substance that formed on the watch
glass after heating
Naphthalene crystal (Solid)
Condition of impure naphthalene on
the beaker glass after heating
Almost all of the naphthalene was
transformed into solid crystal, while
the sand left in the beaker glass and
some of them were being fleck which
attached tightly on the beaker glass.
Table 1: observation table
Result in naphthalene sublimation
Some errors that could have been made in this experiment include:
1. Not measuring the 2 grams of unknown mixture in the beginning of the
experiment
2. Rushing through the experiment by not letting the sand fully dry, not letting the
naphthalene sublimate for 30 minutes.
3. If water got on the underside of the evaporating dish ir inside the flask during
naphthalene sublimation, it would affect the naphthalene from sublimating into
a gas
V. Conclusion
The impure naphthalene (the mixture of naphthalene and sand) can be purified by
doing sublimation.
VI. Suggestion
a. Do not put the mixture on the big flame.
b. Do not inhale the naphthalene vapor
c. Wait until there is no more vapor inside before opening the watch glass. So
make sure that all vapor has already change to crystal before weight it.
VII. Prelab Activity
A. Questions
1. What is sublimation?
2. What will happen if the mixture of naphthalene and sand are heated?
3. What is the mass proportion between sand and naphthalene?
4. In the final condition (after sublimation), the mass of naphthalene will be
more or less?
B. Answer
1. Sublimation is the process of transition of a substance from the solid phase to
the gas phase without passing through an intermediate liquid phase.
Sublimation is an endothermic phase transition that occurs at temperatures and
pressures below a substance's triple point in its phase diagram.
2. When the mixture of sand and naphthalene are heated, there will be vapor
appears from naphthalene indicates that the naphthalene is sublimate. As the
naphthalene sublimate the vapor comes upwards but because the entrance is
blocked by cold watch glass, finally the sublimated vapor is transferred into
crystal.
3. The mass proportion between sand and naphthalene is 1: 2 i.e. 1 gram for sand
and 2 grams for naphthalene.
4. The mass of naphthalene before and after sublimation should be same according
to chemical reaction theory which stated that: “In chemical reaction, mass before
and after reaction is same” but the percentage would be differ from 100%
because there will be rushing and not letting naphthalene sublimate completely,
so that the mass will be less than before.
VIII. Post-lab Activity
A. Questions
1. What are the properties of naphthalene?
2. Why do ice cubes are used on the sublimation?
3. Explain mixture separation by using scheme?
B. Answers
1. Naphthalene is volatile, and easy to evaporate although in solid phase. The
produced vapor is flammable. Naphthalene mostly produced by coal
distillation. Naphthalene is the hard matter which is white and has its own
smell.
2. Ice cubes are needed for cooling down the watch glass that will block the
current of naphthalene vapor to be sublimated into crystal.
3. mixture separation scheme that involves sublimation of naphthalene
References
1. Associate Professor Supawan Tantayanon, (2011) Small Scale Laboratory: Organic Chemistry at University Level. Thailand: UNESCO
2. Zubrick, James W. (2011) The Organic Chemistry LabSurvival Manual. Newyork: Wiley