Salts and Preparation of Salts

normal salts

all hydrogen ions in an acid are replaced by metal and ammonium ions

acid salts

some of the hydrogen ions in an acid are replaced by metal and ammonium ions

preparation of insoluble salts

ionic precipitation

ionic precipitation

two soluble salts in solution reacts to form an insoluble salt i.e. a precipitate and a soluble salt

preparation of soluble salts

direct combination, the reactions with acids and titration

Direct combination

Salts composed of two simple ions can be prepared by reacting two elements, a metal and a non-metal directly with each other

Reactions with acids

reaction between a reactive metal, an insoluble carbonate or an insoluble base and an acid

Titration

Potassium, sodium and ammonium salts are prepared by adding an acid to an aqueous alkali until the solution is just neutral, indicating that the reaction has reached completion.

Potassium, sodium and ammonium salts

can’t be prepared by reaction with acids and direct combination because they’re soluble and too reactive

preparation of insoluble salts method (iconic precipitation)

1. Choose two soluble salts, one containing the cations required to make the salt and the other containing the anions.

2. Dissolve the two salts in water to make solution

3. Mix the two solutions to form the insoluble salt as a precipitate

4. Filter the mixture and collect the precipitate as the residue.

5. Wash the residue with distilled water while it is still in the filter funnel and leave it to dry

Reaction with acid method

1. Choose the appropriate reactive metal, insoluble carbonate or insoluble base to provide the cations and the appropriate acid to provide the anions.

2. Place the acid into a beaker and add the metal, carbonate or base until excess solid remains and effervescence stops if a metal or carbonate is used. This indicates that all the acid has reacted. Heating may be required to speed up the reaction when using a metal or a base.

3. Dip a piece of blue litmus paper into the solution to ensure all the acid has reacted. The litmus should remain blue.

4. Remove the excess, unreacted solid by filtration.

5. Collect the filtrate and evaporate the water over a beaker of boiling water. If hydrated salt is required, evaporate some of the water to concentrate the solution and leave the concentrated solution to crystallise

Titration method

1. Choose an appropriate alkali or soluble carbonate to provide the cations and an appropriate acid to supply the anions.

2. Measure a fixed volume of the aqueous alkali or carbonate using a pipette.
   Run it into a conical flask and add a few drops of indicator solution, e.g. phenolphthalein.

3. Place the acid in a burette and take an initial burette reading.

4. Add the acid to the aqueous alkali or carbonate until the neutralisation point is reached.

5. Take a final burette reading and determine the volume of acid added.

6. Repeat the titration until you have three volumes of acid within 0.1 cm of each other. Average these volumes to determine the volume of acid needed.

7. Add this volume of acid to the fixed volume of aqueous alkali or carbonate without the indicator.

8. Evaporate the water from the solution.