Chapter 3 - Crystal Chemistry 3a - Growing Crystals
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Chapter 3 - Crystal Chemistry 3a - Growing Crystals
Experiment 3.6
Ammonium chloride crystals
• ammonium chloride
• test tube
• crystallising dish
• dropping pipette
• small mirror or
piece of glass
Put ½ measure of ammonium chloride into a clean dry test tube,
add 2cm of water, and shake the test tube until the ammonium
chloride has dissolved. Pour the solution into a crystallising dish.
Use the dropping pipette to put some of the solution onto a small
mirror or a piece of clean glass. Put the mirror somewhere warm
for the water to evaporate.
You can clearly see ammonium chloride crystals on the mirror.
Which of the 3 shapes shown on page 22 do ammonium chloride
crystals most resemble? Their beauty is best seen if you look at
them through a magnifying glass.
Experiment 3.4
Sodium chloride crystals
• sodium chloride
• test tube
• conical flask
• beaker
• funnel
• drinking glass
Fill 6cm of a test tube with solid sodium chloride. Use the funnel to
transfer it from the test tube into the conical flask. Add 20ml of hot
water (measured in your beaker). Gently shake the flask to help the
sodium chloride dissolve. It may not all do so. Allow the solution
to cool.
Pour the solution into a glass container with a clear bottom
(a drinking glass is ideal) and leave it somewhere warm.
Look at the container each day. You will see crystals of sodium
chloride forming in the bottom of the container (some may also
form on the surface)
Which of the 3 shapes shown on page 22 do sodium chloride
crystals most resemble? You can see the crystals more clearly
if you look up at the bottom of the container.
Experiment 3.5
Magnesium sulphate crystals
• magnesium sulphate
• beaker
• test tube
• small saucepan
• glass container
There is a sample of magnesium sulphate in the Chemistry Lab, but
to carry out this experiment you will need to buy more. It is sold as
Epsom Salts. Magnesium sulphate has this name because it is an
important chemical in drinking water, that was first found in spring
water at Epsom in Surrey over 300 years ago in 1695.
Put half a beaker-full (60g) of magnesium sulphate into a small
saucepan and add 3 test tube-fulls (60ml) of water. Heat, whilst
stirring, until the magnesium sulphate has dissolved. Allow it to cool
and then pour it into a glass container. Put this to stand undisturbed
in a warm place. As the water evaporates away a mass of clear
ice-like crystals of magnesium sulphate are formed. Which of the
3 shapes shown on page 22 do magnesium sulphate crystals most
resemble?
Sometimes magnesium sulphate crystallises as big crystals over
a period of time, sometimes as small crystals quickly. Exactly what
will happen will depend on the conditions, such as how slowly the
solution cools, how warm it is where you are keeping it, and how
much it gets disturbed. If small crystals grow, try again. You can
safely experiment using a slightly larger or slightly smaller quantity
of magnesium sulphate.
Experiment 3.7
Sodium thiosulphate crystals
• sodium thiosulphate
• test tube
Put 9 measures of sodium thiosulphate into a clean dry test tube.
Gently heat the crystals moving the test tube continually in the burner
flame. Continue heating until all the solid has melted. Put the HOT
test tube into an empty beaker and allow it to cool
. The cold liquid
has more solid dissolved in it than it can hold, it is
supersaturated
.
Get 1 small crystal of sodium thiosulphate and hold the test tube
level with your eye. Drop the crystal into the liquid. Watch carefully
and describe what you see.