A precipitate is produced when an alkaline solution is added to a solution containing some metal ions - Edexcel - GCSE Chemistry - Question 8 - 2022 - Paper 1

To identify the solutions containing Ca²⁺ and Al³⁺ ions, follow these steps:

1. Prepare a small amount of both solutions (Solution A and Solution B).
2. Add Sodium Hydroxide (NaOH) to each solution separately:
   • A white precipitate indicates the presence of Ca²⁺ ions, as calcium hydroxide is only slightly soluble in water.
   • If no precipitate forms, the solution may contain Al³⁺ ions.
3. Perform a second test for Al³⁺ ions:
   • Add excess NaOH to the solution that previously showed no precipitate. If a white precipitate forms, it indicates the presence of Al(OH)₃, confirming it is the solution with Al³⁺ ions.
4. Conclusion: Compare both reactions to identify Solution A as containing Ca²⁺ ions and Solution B as containing Al³⁺ ions (or vice versa, depending on which is tested first).