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A soluble salt can be prepared by reacting an acid with a suitable insoluble reactant including:

• a metal
• a metal oxide
• a carbonate

The insoluble reactant chosen depends upon the particular salt required. For example, copper does not react with dilute acids, so copper salts are made using copper oxide or copper carbonate, not copper metal. On the other hand, sodium is too reactive to be used safely - again the metal is not used to make sodium salts.

As the reaction between metals and acids produces flammable hydrogen, chemists usually make salts by reacting a metal oxide or a metal carbonate with an acid.

Learn more on salt formation in this podcast.

Listen to the full series on ���˿��� Sounds.

Naming salts

The name of a salt has two parts. The first part comes from the metal, metal oxide or metal carbonate. The second part comes from the acid:

• hydrochloric acid produces chloride salts
• nitric acid produces nitrate salts
• sulfuric acid produces sulfate salts

The table shows some examples of the salts produced by different combinations of insoluble reactants and acids.

Making a salt

To make a soluble salt from an acid and an insoluble reactant:

1. Add some dilute hydrochloric acid to a beaker.
2. Add powdered insoluble reactant to some acid in a beaker, one spatula at a time, stirring to mix. The mixture will effervesce. Continue adding powder until some unreacted powder is left over - it is in excess.
3. Filter the mixture in the beaker to remove the excess powder.
4. Allow the water in the solution to evaporate (by heating and/or leaving for a few days) to obtain pure dry crystals of the salt.

Notes on each step

• To make sure all of the acid has reacted, add the excess of the solid reactant.
• Filtering removes the unreacted insoluble reactant from the salt solution.
• As the acid is all used up and the insoluble reactant has been removed, this only leaves the salt and water. Therefore evaporating the water leaves the pure salt.