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Experiment 11.8
Large sugar crystals - making rock candy
• sugar
• heatproof glass container
• saucepan
• beaker
• strong thread
• large piece of clay pot
• pencil
This last experiment is a treat to celebrate that you have now
carried out all the experiments in this booklet. (You have done
them all haven’t you?)
In Chapter 3 you made crystals of a number of different chemical
substances. Here you will make a large crystal which you can eat.
You will need the help of an adult for this experiment
as you have
to make a large quantity of very hot sugar solution.
Get a large glass container into which you can safely put hot sugar
solution. A 1 pint Pyrex glass kitchen measuring jug is ideal. A jam
jar is not suitable as the hot sugar solution may crack it.
Fill the container with water to within 3cm of the top and measure
this volume of water. You can use your beaker to do this, keep filling
the beaker with the water 100ml at a time and count how many
beaker-fulls there are.
You need to put ½ of this volume of water into a saucepan and add
2½ times as much sugar (by volume) as water. If, for example, you
do use a kitchen measuring jug then when it is filled to within 3cm of
the top it contains 500ml. So you would put 250ml of water and
625ml (note measured by volume) of sugar into the saucepan.
Heat and stir the mixture of sugar and water until it boils. Once it
boils STOP STIRRING and continue boiling gently for 2 minutes. This
sugar syrup is VERY HOT. Let it cool for 5 minutes and then pour it
carefully into the glass container. It should almost fill it. When the
syrup is cool enough to handle move the container
to a place where you can easily see it. Cover it with a piece of
kitchen roll to keep out dust, flies, etc. Leave for 2 or 3 days by
which time there should be some sugar crystals on the bottom (and
maybe floating on the top) of the container. If none have formed put
a sprinkle of sugar into the syrup.
Experiment 11.8
Large sugar crystals - making rock candy
(continued...)
When some sugar crystals have formed, pour off the syrup into a
temporary container and get a lump of the sugar crystals. This will
be your
seed crystal
. Pat it dry with kitchen roll and tie a piece of
strong thread around it.
Wash the sugar out of the container, dry it and put the syrup back
into it. Hang the seed crystal from a pencil resting across the top
of the glass container as in the diagram in Experiment 3.8. The seed
crystal wants to hang in the middle of the container.
The next part is the most difficult.
Let the syrup solution stand
for two or more weeks WITHOUT TOUCHING IT
. If you move the
container it may spoil the experiment. Day by day you should see
the seed crystal grow into a large irregular lump of sugar candy.
When you can wait no longer remove the sugar candy from the
syrup. Do this in a sink as there will be a lot of sticky sugar syrup
to throw away. Quickly wash the syrup off the crystals and pat them
dry with kitchen roll. Keep the candy in a dish and eat it a little at a
time, but remember that sugar is very bad for your teeth, so don’t
eat too much and thoroughly clean your teeth afterwards.
Chapter 11 - Some sugar chemistry
Chapter 11 - Some sugar chemistry