Experiment:
Growing Crystals
When substances change from a liquid or gas to a solid, they can form
crystals. In a crystal the molecules of the material
lock together in
a regular and repeating pattern. If a crystal is allowed to grow
undisturbed, it will form regular shapes such as cubes, or hexagon
columns. The type of substance and how its molecules interlock determine
the shape of the crystal.
You can grow your own crystals at home. For this experiment you will
need
a plastic or paper cup, sugar or salt (about a cup of either),
and a pan for heating water. If
you want to make both sugar and salt crystals you will need two cups.
Note:
The following experiment requires the heating of water with
a flame
and should ONLY be done under adult supervision.
STEP 1
-
Put a half a cup of tap water into the pan.
STEP 2 - Heat the water over a flame. If you are going to make
salt
crystals you need only heat the water to around 140 degrees. If you are
going to make sugar crystals, bring the water up to boiling.
STEP 3 - Pour the sugar or salt into the water and stir. Keep
adding
more until it will no longer dissolve. Then add just a little more
water and continue to heat and stir until all the material disappears.
STEP 4 - Turn off the burner and let the water cool to room
temperature.
STEP 5
- Pour the contents into the paper or plastic cups.
STEP 6 - Put the cup somewhere where it will not be disturbed until
the
liquid evaporates. This could take several weeks.
When you check the cup after all the liquid is gone you should see crystals
coating the sides and bottoms of the cups.
If you made
both sugar (above right) and
salt crystals (right), notice they form different shapes.
A variation to the above experiment will give you larger and more
regularly-shaped crystals This will require a pencil, string, and a weight
(like a small metal nut or washer). After STEP 6:
STEP 7 - Tie the
string to the middle of the pencil and tie the weight
to the other end of the string. Make sure the distance between the
weight and the pencil is less than the depth of the cup.
STEP 8 - Put the pencil across the top of the cup so that the string
and weight hang in the cup. The crystals will form on the string as the
liquid evaporates.
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