Download 20. The sublimation of air freshener

Classic chemistry experiments
20.
49
The sublimation of
air freshener
Topic
Sublimation, separation, purification.
Timing
30 min.
Description
Students use an air freshener in a water bath to demonstrate sublimation.
Apparatus and equipment (per group)
3
▼ Two 100 cm beakers
▼ Shallow dish
▼ Thermometer
▼ Access to a fume cupboard.
Chemicals (per group)
▼ Small piece of solid air freshener
▼ Ice
▼ Hot water.
Teaching tips
It is possible to use other materials that sublime. Solid toilet bowl cleaners work best,
but if cheap ones that contain p-dichlorobenzene are used, handle them with tongs in
the fume cupboard as this substance is harmful. If iodine is used, use only a few
crystals and do the activity in a fume cupboard. Iodine is also harmful. Naphthalene
(Harmful) mothballs must be heated to near 70 °C to sublime. Dry ice sublimes at
–78.5°C and above. If possible use a coloured air freshener, notice that the material
that collects on the cold beaker is white. The dye does not sublime because it is not
chemically a part of the compound that does sublime. Vapour deposition is an
important industrial process for separation and purification.
Gel type air fresheners – eg Glade – do not work.
Background theory
Sublimation is the vaporisation of a solid. The opposite process, the formation of a
solid directly from a vapour, is called deposition. The heat from the water bath causes
the solid air freshener to sublime. The cold beaker causes the vaporised air freshener to
condense and re-form the solid.
Safety
Wear eye protection. Most of these substances are harmful. In day to day use at room
temperature, this does not present a problem, as the vapour pressure is relatively low.
However, if heated until they sublime, vapour levels could reach hazardous
concentrations. Hence, either a fume cupboard should be used or some other method
of preventing escape into the air.
50
Classic chemistry experiments
Answers
1. The air freshener does not sublime measurably below this temperature.
2. Sublimation is the physical change that occurs when a substance goes from a solid
phase directly to a gaseous phase.
3. Particles go from being close-packed and ordered in a solid to separated and
disordered in a gas.
Classic chemistry experiments
51
The sublimation of
air freshener
Introduction
Sublimation is an interesting physical change. When a substance sublimes, it changes
directly from a solid to a gas without passing through the liquid state. Dry ice sublimes,
as do iodine and mothballs. This experiment involves the study of another common
substance that sublimes – air freshener.
Ice
LOOK HERE
Dish
Hot water
Piece of air freshener
What to do
3
1. Place a few lumps of air freshener in the bottom of the 100 cm beaker.
3
3
2. Put the 100 cm beaker carefully on top of the other 100 cm beaker.
3. Fill the top beaker three quarters full with ice. Ensure no ice enters the beaker
below.
4. Fill the shallow dish or pan about one-third full of hot water (at a higher
temperature than 45 °C).
5. Place the sublimation apparatus in the shallow dish in a fume cupboard.
6. Observe what happens to the solid. Be patient, it may take a while.
Safety
Wear eye protection. Use a fume cupboard.
Questions
1. What might be the significance of 45 °C? Try lower and higher temperatures if
there is time.
2. Define ‘sublimation’.
3. Use the particle theory of matter to explain what is happening and include a
particle diagram.