Naming and making salts

Common table salt is sodium chloride, but it is just one example of many compounds called salts. The name of a salt has two parts:

  • the first part comes from the metal in the base used
  • the second part comes from the acid that was used

Making potassium nitrate

Where does the name potassium nitrate come from?

The words 'Potassium nitrate' labelled to show that potassium comes from a base containing potassium such as potassium hydroxide. The nitrate comes from nitric acid.

These are the rules for the second part of the name of a salt:

Acid usedSecond part of salt's name
hydrochloric acidchloride
sulfuric acidsulfate
nitric acidnitrate

Example 1: copper sulfate

How can we make copper sulfate? The first part of the name is 'copper', so we need a base containing copper. We could use copper oxide or copper carbonate, for example. The second part of the name is 'sulfate', so we need to use sulfuric acid.

Here are the equations for those reactions:

copper oxide + sulfuric acid → copper sulfate + water

CuO + H2SO4 → CuSO4 + H2O

copper carbonate + sulfuric acid → copper sulfate + water + carbon dioxide

CuCO3 + H2SO4 → CuSO4 + H2O + CO2

Copper oxide and copper carbonate are insoluble, so usually you add an excess (more than enough to react with all the acid) then filter the mixture. The excess solid stays in the filter paper as a residue. The copper sulfate solution drips through as a filtrate. This can be warmed to evaporate the water, leaving copper sulfate crystals behind.

Copper sulfate crystal
Copper sulfate forms blue crystals

Example 2: sodium chloride

How can we make sodium chloride? The first part of the name is 'sodium', so we need a base containing sodium. We could use sodium hydroxide, which is soluble and so forms an alkaline solution. The second part of the name is 'chloride', so we need to use hydrochloric acid.

Here are the equations for the reaction:

sodium hydroxide + hydrochloric acid → sodium chloride + water

NaOH + HCl → NaCl + H2O

It can be difficult to add exactly the right amount of acid and alkali in a neutralisation reaction so that your salt solution is precisely pH 7. You can check the reaction mixture using universal indicator or a pH meter to see when it becomes pH 7, but a little acid or alkali is often left over. So it would not be safe to taste the sodium chloride solution produced.

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