Prepare an Insoluble Salt (Edexcel IGCSE Chemistry)

Spec point — describe an experiment to prepare a pure, dry sample of an insoluble salt, starting from two soluble reactants

Prepare an insoluble salt

• 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 an insoluble 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 salt 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

  • 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.