Salts are always made from an acid and an alkali.
All salts consist of
, which are charged particles.
Not all salts are soluble.
Examples of salts in use today are...
Calcium sulphate - used as gypsum in plaster of Paris.
Potassium chloride - used by people cutting forn the sodium in their diet.
Cobalt sulphate - used as a pigment in paint.
Barium sulphate - used for barium meals in medicine.
Making a salt depends on whether the salt is soluble or
in water.
Soluble Salts | Insoluble Salts |
All | |
All chlorides except | chloride and lead chloride |
All sulphates except | barium sulphate and sulphate |
and sodium carbonates | all other carbonates |
Precipitation ReactionsMethod for Insoluble Salts.For example silver chloride is made from silver nitrate and sodium chloride. The silver chloride makes a solid which becomes a precipitate. The left over sodium and nitrate ions stay in solution.
There are 4 steps in this procedure.
1. Mix solutions of 2
salts that contain the right ions
2. Filter off the
3. Wash the precipitate with
water
4. Leave the precipitate to dry at room temperature or in a
oven.
Making soluble saltsMethod 1 for Soluble Salts1. Measure the right volume of
into a beaker. Add the metal or insoluble oxide/hydroxde/carbonate a little at a time until no more dissolves.
2. Filter off the excess solid and collect the
.
3. Heat the solution gently to
some of the water.
4. Pour the concentrated solution into an evaporating dish and leave to cool and crystallise.
Method 2 for Soluble Salts1. Measure the right amount of alkali or carbonate into a flask. Add a few drops of
.
2. Add the
gradually. Stop when the indicator changes colour.
3. Add a spatula of
powder to absorb the indicator. Heat.
4. Filter to remove the charcoal powder.
5. Heat gently to
.
6. Pour into a shallow dish and leave to cool and crystallise.