Working in your Chemistry Laboratory continued... Working in your Chemistry Laboratory continued...
10 11
SAFETY TIP: The use of clay pot.
You can considerably reduce the risk of an
accident due to the contents of a test tube
spurting out, by putting one or two small
pieces of clay pot into the tube. As the
water boils the steam is formed as tiny
bubbles on the sharp points of the clay pot
and these then bubble smoothly out of the
solution.
See Note 2 at the beginning of “The
Chemistry Experiments” where how to
make the pieces of clay pot is described.
Never heat a test tube with a cork in it.
If you have hot water in the test tube you can
safely put it into the test tube rack. If you have
a hot solid in the tube then the tube may be
VERY HOT and could melt the test tube rack
– put the hot tube into an empty beaker and
leave it there until it is cool.
Cleaning The Test Tubes
Wash them with running water and clean with
the test tube brush. If necessary use a little
washing-up detergent. The outsides of the
test tubes will get black with deposits from
the burner. Clean this off with a cream kitchen
cleaner such as Cif. To dry inside test tubes
use rolled up kitchen paper towel.
Your Water Supply
For washing dirty equipment a tap and
sink are best. When carrying out the
experiments you will need a “water bottle”
for adding small quantities of water, in a
controlled way, to the chemicals in the test
tubes. Two suggestions are a “Washing-up
Detergent Bottle” or a “Hand Sprayer”.
TIP: A Washing-up Detergent Bottle.
Remove the cap from an empty bottle
(or better get an adult to do so for you by
prizing the cap off with the edge of a knife)
and thoroughly wash the bottle and,
particularly, the cap to remove all traces
of detergent.
You can fill the bottle with water, replace
the cap and use it by gently squeezing the
bottle. However, the jet of water you get is
rather too much. The bottle can be
considerably improved for your purpose if
you get an adult to heat a needle held in
a pair of pliers in your Spirit Burner flame
and melt a small hole through the centre
of the top of the cap. Then click shut the
top of the cap and squirt the water out of
this fine hole.
continued...
SAFETY TIP: Using the Spirit Burner.
You can extinguish the burner flame by
blowing it out, but a good tip to follow is
to have a heat proof drinking glass that fits
over the burner. To extinguish the flame
just put the glass upside down over the
burner and after a few seconds the flame
will go out. (Do you know why?
Experiments 9.8 and 9.17 have the
answer).
Leave the glass in place until you next
want to use the burner.
YOU THEN ALWAYS KNOW THAT IF
THE BURNER IS NOT UNDER THE
GLASS, IT IS ALIGHT.
NEVER LEAVE CHILDREN UNATTENDED
WITH THE SPIRIT BURNER.
Using The Test Tubes
For these experiments you will usually be
using less than 3cm depth of water in the
test tubes. Do not overfill as the more liquid
you have in a test tube the more difficult it is
to control any boiling that occurs. Solids can
be added to a test tube with the measuring
spoon. You might find it easier to add liquids
by using the funnel, or by pouring the liquid
into a beaker and then into the test tube.
Heating A Test Tube:
Always point the test tube away from you
and other people. Hold the test tube in the
test tube holder whenever you are likely to
boil the contents or heat them strongly.
TIP: A wooden clothes peg also makes
a good test tube holder.
The easiest way to dissolve solids in water is
to put a cork in the test tube and shake it. If
the solid does not dissolve after about 15
seconds of shaking then gently warm the
solution.
Most solids dissolve more readily in water if
you gently warm the solution. You can hold
the tube without the holder if you are only
going to heat it for a few seconds to get the
water warm to help a solid dissolve. To heat
a tube hold it in a slanting position away
from you and continually move it about in the
flame. Even when told to heat a tube
strongly, start with gentle heating and watch
carefully in case the contents spit or spurt
out of the tube.
