Naming salts

Acids are neutralised by bases, including alkalis, and metal carbonates.

Reactions with bases, including alkalis

Metal oxides are bases. In general, when an acid reacts with a metal oxide, the products are a salt and water.

Acid + metal oxide → salt + water

For example:

Sulfuric acid + copper oxide → copper sulfate + water

H2SO4(aq) + CuO(s) → CuSO4(aq) + H2O(l)

Alkalis are soluble bases. A salt and water are produced when acids react with alkalis. In general:

Acid + alkali → salt + water

For example:

Nitric acid + sodium hydroxide → sodium nitrate + water

HNO3(aq) + NaOH(aq) → NaNO3(aq) + H2O(l)

Reactions with carbonates

A salt, water and carbon dioxide are produced when acids react with carbonates. In general:

Acid + carbonate → salt + water + carbon dioxide

For example:

Hydrochloric acid + copper carbonate → copper chloride + water + carbon dioxide

2HCl(aq) + CuCO3(s) → CuCl2(aq) + H2O(l) + CO2(g)

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 ions is equal to zero. The formulae of some common ions are given below:

Charge on ionExamples
+1K+, Na+, Li+
+2Mg2+, Ca2+, Cu2+, Fe2+
+3Al3+, Fe3+
-1Cl-, Br-, I-, NO3-
-2SO42-
-3PO43-

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