Making salts from acids and bases

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(II) oxide or copper(II) 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.

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.

Hydrochloric acidSulfuric acidNitric acid
Copper(II) oxideCopper(II) chlorideCopper(II) sulfateCopper(II) nitrate
Aluminium hydroxideAluminium chlorideAluminium sulfateAluminium nitrate
Zinc carbonateZinc chlorideZinc sulfateZinc nitrate

Making a salt

This method shows how a soluble salt is produced from an acid and an insoluble reactant. To illustrate the method, hydrochloric acid and zinc carbonate are used:

  1. Add some dilute hydrochloric acid to a beaker.
  2. Add powdered zinc carbonate to some acid, one spatula at a time, stirring to mix. The mixture will effervesce.
  3. Continue adding powder until it is in excess (some unreacted powder is left over).
  4. Filter the mixture in the beaker to remove the excess zinc carbonate.

Pure dry crystals of zinc chloride can be produced by crystallisation, then filtration to remove excess solution, followed by drying on a watch glass or in a warm oven.

Reasons for each step

  1. the acid is warmed to make the reaction faster
  2. the mixture will fizz because the reaction of an acid with a carbonate produces carbon dioxide gas
  3. if there is an excess of the solid reactant, all of the acid will react
  4. the unreacted insoluble reactant is removed, leaving a solution containing only the salt and water