Naming salts
acidSubstance producing more hydrogen ions than hydroxide ions when dissolved in water. are neutralisationThe reaction between an acid and a base to form a salt plus water. by baseA substance that reacts with an acid to neutralise it and produce a salt., including alkaliSubstance producing more hydroxide ions than hydrogen ions when dissolved in water., and by metal carbonateSubstance containing carbonate ions. Most carbonates are insoluble (such as calcium carbonate) but sodium carbonate and ammonium carbonate are soluble in water..
Reactions with bases, including alkalis
Metal oxides are bases. In general, when an acid reacts with a metal oxide, the products are a saltThe substance formed when the hydrogen ion in an acid is replaced by a metal ion. and water.
Acid + metal oxide 鈫 salt + water
For example:
Sulfuric acid + copper oxide 鈫 copper sulfate + water
H2SO4(aq) + CuO(s) 鈫 CuSO4(aq) + H2O(l)
Alkalis are soluble bases. A salt and water are produced when acids react with alkalis. In general:
Acid + alkali 鈫 salt + water
For example:
Nitric acid + sodium hydroxide 鈫 sodium nitrate + water
HNO3(aq) + NaOH(aq) 鈫 NaNO3(aq) + H2O(l)
Reactions with carbonates
A salt, water and carbon dioxide are produced when acids react with carbonates. In general:
Acid + carbonate 鈫 salt + water + carbon dioxide
For example:
Hydrochloric acid + copper carbonate 鈫 copper chloride + water + carbon dioxide
2HCl(aq) + CuCO3(s) 鈫 CuCl2(aq) + H2O(l) + CO2(g)
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 base, alkali 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
Question
Predict the name of the salt formed when copper oxide reacts with nitric acid.
The salt formed is copper nitrate.
Deducing the formulae of salts
A salt has no overall charge, since the sum of the charges on their ionElectrically charged particle, formed when an atom or molecule gains or loses electrons. is equal to zero. The formulaA combination of symbols that indicates the chemical composition of a substance. of some common ions are given below:
| Charge on ion | Examples |
| +1 | K+, Na+, Li+ |
| +2 | Mg2+, Ca2+, Cu2+, Fe2+ |
| +3 | Al3+, Fe3+ |
| -1 | Cl-, Br-, I-, NO3- |
| -2 | SO42- |
| -3 | PO43- |
| Charge on ion | +1 |
|---|---|
| Examples | K+, Na+, Li+ |
| Charge on ion | +2 |
|---|---|
| Examples | Mg2+, Ca2+, Cu2+, Fe2+ |
| Charge on ion | +3 |
|---|---|
| Examples | Al3+, Fe3+ |
| Charge on ion | -1 |
|---|---|
| Examples | Cl-, Br-, I-, NO3- |
| Charge on ion | -2 |
|---|---|
| Examples | SO42- |
| Charge on ion | -3 |
|---|---|
| Examples | PO43- |
Notice that ions of group 1 elements have a charge of +1, and ions of group 2 elements have a charge of +2. The group 7 element ions have a charge of -1, and the group 6 element ions have a charge of -2.
Example
What is the formula of aluminium sulfate?
The formulae of the ions are Al3+ and SO42-.
The sum of the charges on the ions in the neutral salt must be zero. Two Al3+ ions have a total charge of +6 and three SO42- ions have a total charge of -6.
So the formula is Al2(SO4)3.
Question
What is the formula of magnesium chloride?
MgCl2