• A soluble salt can be made from the reaction of an acid with an insoluble base
• During the preparation of soluble salts, the insoluble reactant is added in excess to ensure that?all?of the?acid?has?reacted
• If this step is not completed, any unreacted acid would become?dangerously?concentrated during evaporation and crystallisation
• The excess reactant is then removed by?filtration?to ensure that only the salt and water remain
• Since all of the acid has reacted and the excess solid base has been removed then the solution left can only be salt and water
• If a carbonate was used as the solid base instead of an oxide or hydroxide, then any carbon dioxide gas produced would have been released into the atmosphere
• A common example is the preparation of copper(II) sulfate which can be made with copper(II) oxide and dilute sulfuric acid:

CuO (s) + H₂SO_4?(aq) ? CuSO_4?(s) + H₂O (l)

• The acid could also be reacted with a metal to produce the salt, as long as the metal is above hydrogen in the reactivity series and not too reactive so that a dangerous reaction does not take place