Report Sublimation

International 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.

1pc

Tripod

7. Digital balance

1pc

8. Road Stirrer

1pc

9.

Ice

5pc

Chemical: 1.

Naphthalene

2. Sands

III.

2gr 1gr

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

Result in naphthalene sublimation

 Analysis of impure naphthalene Changes that occur during heating (in

There was fog inside the beaker glass

beaker glass)

indicated that the naphthalene began to sublimated

Changes that occur during heating (in

The

ice melted while there were

watch glass)

crystals begun to be formed on part of  watch glass inside the beaker glass

Substance that formed on the watch

Naphthalene

crystal (Solid)

glass after heating Condition of impure naphthalene on

Almost all of the naphthalene was

the beaker glass after heating

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

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: I n 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. distillation.

Naphthalene

Naphthalene

mostly produced by coal

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 Lab Survival Manual. Newyork: Wiley