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Chapter 5 - Acids and alkalis 5a - Making acid
and alkali solutions
Experiment 7.1
The formation of copper carbonate
• copper sulphate
• sodium carbonate
solution
• 2 test tubes
• funnel
• filter paper
• small container
• label
Dissolve ½ measure of copper sulphate in 1cm of water in a test
tube. Add 2cm of your sodium carbonate solution. A blue-green
precipitate of copper carbonate is obtained. Filter it off and dry it as
described in Experiment 1.6. Put the copper carbonate in a container,
label it and keep it for using in Experiment 8.6.
Experiment 7.2
The formation of magnesium carbonate
• magnesium sulphate
• sodium carbonate
solution
• sodium hydrogen
sulphate solution
• test tube
Dissolve ½ measure of magnesium sulphate in 1cm of water in
a test tube. Add 2cm of your sodium carbonate solution. A white
precipitate of magnesium carbonate is formed. Magnesium
carbonate readily dissolves in acids. Add a little of your sodium
hydrogen sulphate solution and the precipitate will disappear.
Experiment 7.3
The formation of aluminium hydroxide
• aluminium potassium
sulphate
• sodium hydroxide
solution
• sodium hydrogen
sulphate solution
• 2 test tubes
Dissolve ½ measure of aluminium potassium sulphate in 1cm of
water in a test tube. Add sodium hydroxide solution drop by drop
with the dropping pipette. A white precipitate of aluminium
hydroxide is formed. This shows an unusual property; it will
dissolve in both acids and alkalis. It is said to be
amphoteric
.
Pour half of the solution and precipitate into a second test tube.
Add a little acid (use your sodium hydrogen sulphate solution) to
one test tube of aluminium hydroxide, and a little alkali (use your
sodium hydroxide solution) to the other test tube. The precipitate
dissolves in both tubes. In the acid the aluminium hydroxide forms
aluminium sulphate and in the alkali the aluminium hydroxide
forms sodium aluminate.
Experiment 6.7
The reaction of copper oxide with acid
• copper oxide
• sodium hydrogen
sulphate solution
• 2 test tubes
• test tube holder or
wooden clothes peg
• clay pot
• funnel
• filter paper
• large evaporating spoon
• crystallising dish
Put ½ measure of copper oxide in a clean dry test tube and add
2cm of your sodium hydrogen sulphate solution. Add 2 small pieces
of clay pot. Boil the solution carefully, holding the tube in a test tube
holder or a wooden clothes peg. The clay pot will help the solution
to boil smoothly, but it can still spit and spurt out. WEAR YOUR
GOGGLES and ensure that the test tube is not pointing at anyone.
Boil the solution for about 5 minutes, adding more water if the
amount gets too low. Put the test tube in the test tube rack and let
the black copper oxide settle. What is the colour of the solution?
Filter off the excess copper oxide, wash it in the filter paper with
water and let the washings go in with the filtrate. What is the
substance in the filtrate that makes it pale blue? Concentrate this
solution by boiling off most of the water in your large evaporating
spoon. Only fill the spoon about half full and keep adding more
solution from the test tube as the water boils away. When you have
a tiny volume of water left, pour it into a crystallising dish and leave
it somewhere warm for the mixture of copper sulphate and sodium
sulphate to form crystals as the water slowly evaporates away.
When a metal carbonate reacts with an acid it forms a salt, water
and carbon dioxide. The word equation for the reaction is: metal
car acid salt + water + carbon dioxide.
Experiment 6.8
The reactions of carbonates with acids
• sodium carbonate
• sodium hydrogen
sulphate solution
• test tube
• indigestion tablet
Put ½ measure of sodium carbonate into a test tube and add 2cm of
your sodium hydrogen sulphate solution. A violent fizzing occurs as
carbon dioxide gas is formed.
Repeat the experiment with 1 measure calcium carbonate instead of
sodium carbonate.
Repeat the experiment again, this time with a crushed up indigestion
tablet, or a little indigestion powder (not one that fizzes when you
add water).
What makes some indigestion tablets fizz when you add water?
Chapter 6 - Chemical reactions of acids and alkalis
6c - Reactions of acids with oxides & carbonates
Chapter 7 - Other chemical reactions
7a - Reactions which give insoluble substances
Often when solutions of two chemicals are mixed a solid substance if formed. The solid is called
a
precipitate
.
When a metal oxide reacts with an acid the products are a salt and water. The word equation for
the reaction is: metal oxide + acid salt + water.
