Preparing Insoluble Salts (Cambridge O Level Chemistry)

• 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 filtrate 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

Soluble Salt 1 = lead(II) nitrate        

Soluble Salt 2 = potassium sulfate

Method:

• 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

Equation of reaction:

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

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