Making salts from acids and insoluble reactants
A solubleAble to dissolve in solvent. For example, sugar is soluble in water because it dissolves to form sugar solution. saltThe substance formed when the hydrogen ion in an acid is replaced by a metal ion. can be prepared by reacting an acidSubstance producing more hydrogen ions than hydroxide ions when dissolved in water. with a suitable insolubleUnable to dissolve in a particular solvent. For example, sand is insoluble in water. reactantA substance that reacts together with another substance to form products during a chemical reaction. 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 flammableAble to ignite and burn. 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.
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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 acid | Sulfuric acid | Nitric acid | |
| Copper oxide | Copper chloride | Copper sulfate | Copper nitrate |
| Aluminium hydroxide | Aluminium chloride | Aluminium sulfate | Aluminium nitrate |
| Zinc carbonate | Zinc chloride | Zinc sulfate | Zinc nitrate |
| Copper oxide | |
|---|---|
| Hydrochloric acid | Copper chloride |
| Sulfuric acid | Copper sulfate |
| Nitric acid | Copper nitrate |
| Aluminium hydroxide | |
|---|---|
| Hydrochloric acid | Aluminium chloride |
| Sulfuric acid | Aluminium sulfate |
| Nitric acid | Aluminium nitrate |
| Zinc carbonate | |
|---|---|
| Hydrochloric acid | Zinc chloride |
| Sulfuric acid | Zinc sulfate |
| Nitric acid | Zinc nitrate |
Making a salt
To make a soluble salt from an acid and an insoluble reactant:
- Add some dilute hydrochloric acid to a beaker.
- 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 excessIn chemistry, a substance is in excess if there is more than enough of it to react with another reactant..
- Filter the mixture in the beaker to remove the excess powder.
- Allow the water in the solutionMixture formed by a solute and a solvent. to evaporationThe process in which a liquid changes state and turns into a gas. (by heating and/or leaving for a few days) to obtain pureA substance that consists of only one element or only one compound. dry crystalA solid containing particles (atoms, molecules or ions) joined together to form a regular arrangement or repeating pattern. 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.