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 acids:

  • 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.

Worked 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