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