How to Prepare an Insoluble Salt (Edexcel IGCSE Chemistry)

Prepare an Insoluble Salt

Spec point — 2.27C

• 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
• The preparation of a soluble salt follows this pattern:

soluble salt 1 + soluble salt 2 ⟶ insoluble salt + soluble salt 3

AB + CD ⟶ AD + CB

• The method involves measuring out a fixed volume of one solution and then adding the second salt solution until it is in a slight excess

  • This ensures the maximum amount of precipitate will be obtained

• The precipitate is recovered by filtration and then it must be washed with distilled water remove reactants that are contaminating the residue (recovered solid)

  • It is then left to dry

• This method is a good way to prepare silver and lead(II) salts which are often insoluble; the starting material will usually be the nitrate of silver or lead(II) since all nitrates are soluble

Exam Hint This reaction is also known as a double decomposition reaction.