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Experiment 9.6
The gases produced in a flame
• lime water
• 2 test tubes
• cork for test tube
• test tube holder or
wooden clothes peg
You produce carbon dioxide by “burning” food inside you. When any
carbon containing material burns it produces carbon dioxide. The
methylated spirits in your spirit burner contains carbon.
Have ready a cork (NOT a plastic stopper) for a test tube. Using a test
tube holder or a wooden clothes peg hold a clean dry test tube upside
down about 1cm above the burner flame for about 1 minute. THE TOP
OF THE TEST TUBE JUST ABOVE THE FLAME WILL GET VERY HOT SO
TAKE GREAT CARE NOT TO BURN YOURSELF. Quickly put the cork in
the test tube and leave the test tube for some time until it is cool.
When the test tube is cold, remove the cork, add a little lime water,
replace the cork and shake the tube. Does the lime water go milky?
Also when the methylated spirits burns it produces water, as steam.
You can show this by filling a test tube ½ full of cold water, wiping the
outside of the tube completely dry and holding the tube above the burner
flame for about 5 seconds. A thin film of water vapour appears on the
outside of the test tube where the hot gases from the burner have
condensed on the cold tube.
You will also have noticed that when using the burner your test tubes
get a black deposit on them. What is this?
Experiment 9.7
The reaction of carbonates with acid
• sodium hydrogen
sulphate solution
• sodium hydrogen
carbonate (sodium
bicarbonate)
• vinegar
• aluminium foil
• lime water
• 2 test tubes
• glass & rubber tubing
• cork for test tube with
hole
• lolly stick
• sellotape
• pair of scissors
In Experiment 6.8 you carried out the reaction between carbonates and
an acid and saw a violent fizzing. You did not test to show that the gas
was carbon dioxide by passing it through lime water. This is difficult to
do as the reaction is so quick you do not have time to assemble the
bubbling apparatus (as in Experiment 9.5) in time.
In this experiment a trick is used to slow down the reaction long
enough for you to put the apparatus together.
Have ready 3 or 4cm of lime water in a test tube, and have your
gas-tube all assembled.
Cut a 4cm square of aluminium foil and fold it round a lolly stick to
make a packet. Let the end of the foil extend over the end of the stick
and fold it over to make a sealed bottom. Put a piece of sellotape on
the foil edge to hold the packet together and slide it off the lolly stick.
It should be about 3½ cm long.
Continued...
Experiment 9.4
To identify the gas in sparkling water (first experiment)
• sparkling water
• universal indicator paper
• test tube
• dropping pipette
Because carbon dioxide is an acid, with the characteristic sharp sour
taste, it is used to put the fizz into sparkling water and fizzy drinks. It is
also the gas in beer. In Experiment 5.11 you used universal indicator
paper to test the acidity of sparkling water. You can carry out a more
accurate test by using universal indicator in solution.
Pour some of the universal indicator solution left over from Experiment
9.3 into a test tube and with your dropping pipette add an equal volume
of sparkling water. What is the colour of the indicator? Is it yellow
showing that sparkling water is an acid? If you do not have any
sparkling water you can try a fizzy soft drink, but many flavoured drinks
have other acids, such as citric acid, added to them. This will interfere
with this experiment.
Experiment 9.5
To identify the gas in sparkling water (second experiment)
• sparkling water
• lime water
• 2 test tubes
• glass & rubber tubing
• test tube
• cork with hole
• test tube holder or
wooden clothes peg
• clay pot
For this and later experiments you are going to need the two test tubes
connected with the rubber tubing with one piece of glass tubing fitted
into a test tube with a cork. Assemble this equipment. Read the section
“Using Glassware” at the beginning of this booklet on how to do this.
This is the “gas-tube”.
Put 3 or 4cm of lime water into a test tube. Put 3 or 4cm of sparkling
water (or fizzy soft drink) into a second test tube. Add a piece of clay
pot. Assemble the gas-tube as shown in the diagram and heat the
bottom of the test tube. The gas given off will bubble through the lime
water. Describe what you see. Does the lime water go milky?
Experiment 9.4 might not work properly if you use a fizzy soft drink,
but this experiment will. Why do you think this is?
Chapter 9 - The chemistry of some gases
9a - Carbon dioxide
Chapter 9 - The chemistry of some gases
9a - Carbon dioxide
Lime water
Sparkling water
Spirit burner