Preparing Insoluble Salts (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award)): Revision Note

Preparing insoluble salts

Extended tier only

• Insoluble salts can be prepared using a precipitation reaction

• The solid salt obtained is the precipitate

• To successfully use this method:

  • The solid salt (precipitate) being formed must be insoluble in water

  • The reactants must be soluble

Using two soluble reactants

Diagram showing the filtration of the mixture to remove the precipitate

Method

• Make aqueous solutions of two soluble salts

• Mix together using a stirring rod in a beaker

• Filter to remove the precipitate from the mixture

• Wash the precipitate with distilled water to remove traces of other solutions

• Leave to dry (for example in a warm oven)

Example: Preparation of pure, dry, solid lead(II) sulfate using a precipitation reaction

• Dissolve lead(II) nitrate and potassium sulfate in water

• Mix together using a stirring rod in a beaker

• Filter to remove the precipitate from the mixture

• Wash the precipitate with distilled water to remove traces of potassium nitrate solution

• Leave to dry (for example in a warm oven)

lead(II) nitrate + potassium sulfate → lead(II) sulfate + potassium nitrate

Pb(NO₃)₂ (aq) + K₂SO₄ (aq) → PbSO₄ (s) + 2KNO₃ (aq)