Steps to confirm Al3+ cation using Al2(SO4)3

To confirm the presence of Al³⁺ cation in a salt sample using aluminum sulfate (Al₂(SO₄)₃), follow these steps:

1. Dissolve the salt sample in water to prepare a test solution.
2. Add a few drops of dilute hydrochloric acid (HCl) to the solution to remove any interfering ions.
3. Add ammonium chloride (NH₄Cl) to the solution to maintain a constant concentration of ammonium ions, which helps in the selective precipitation of group III cations.
4. Slowly add ammonium hydroxide (NH₄OH) to the solution while stirring. This will precipitate the aluminum ions as aluminum hydroxide:

Al³⁺ + 3NH₄OH → Al(OH)₃ (s) + 3NH₄⁺

5. Observe the formation of a white gelatinous precipitate of aluminum hydroxide (Al(OH)₃), which confirms the presence of Al³⁺ cations in the salt sample.