Preparing Insoluble Salts (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

Extended tier only

• Insoluble salts can be prepared using a precipitation reaction
• The solid salt obtained is the precipitate, thus in order to successfully use this method the solid salt being formed must be insoluble in water, and the reactants must be soluble

Using two soluble reactants

Diagram showing the filtration of the mixture to remove the precipitate

Method

• Dissolve soluble salts in water and mix together using a stirring rod in a beaker
• Filter to remove precipitate from mixture
• Wash the residue with distilled water to remove traces of other solutions
• Leave in an oven to dry

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

• Dissolve lead(II) nitrate and potassium sulfate in water and mix together using a stirring rod in a beaker
• Filter to remove precipitate from mixture
• Wash precipitate with distilled water to remove traces of potassium nitrate solution
• Leave in an oven to dry

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

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