Preparation of Insoluble Salts | Chemistry for Grade 11 (IGCSE) PDF Download

Preparing Insoluble Salts

• Insoluble salts are formed using a precipitation reaction.
• The solid salt obtained is known as the precipitate. To ensure success, the solid salt formed must be insoluble in water, and the reactants must be soluble.

When two soluble reactants are used, a precipitation reaction occurs. The diagram below illustrates the filtration process to separate the precipitate:

Method

Follow these steps to prepare insoluble salts:

1. Mix two soluble reactants in a solution.
2. A precipitation reaction will occur, forming an insoluble salt as a solid.
3. Filter the mixture to separate the precipitate from the solution.
4. Collect and dry the precipitate to obtain the insoluble salt.

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

Soluble Salts Used

• Soluble Salt 1: lead(II) nitrate
• Soluble Salt 2: potassium sulfate

Method

• Dissolve lead(II) nitrate and potassium sulfate in water. Mix them well in a beaker using a stirring rod.
• Filter the mixture to separate the precipitate.
• Wash the precipitate with distilled water to remove any traces of potassium nitrate solution.
• Allow the washed precipitate to dry in an oven.

Equation of reaction
lead(II) nitrate + potassium sulfate → lead(II) sulfate + potassium nitrate
Pb(NO₃)₂(aq) + K₂SO₄(aq) → PbSO₄(s) + 2KNO₃(aq)