Tscherhigite is a hydrated, water-soluble mineral, with relative formula mass of 453.2 - AQA - A-Level Chemistry - Question 2 - 2022 - Paper 3

1. Test for NH₄⁺ (Ammonium ion):

   • Test: Add NaOH solution to the sample and warm gently.

   • Result: The release of ammonia gas will yield a characteristic smell and can turn red litmus paper blue.

   • Ionic equation:

   NH₄⁺ + OH⁻ → NH₃(g) + H₂O

2. Test for Al³⁺ (Aluminum ion):

   • Test: Add NaOH solution which results in a white precipitate.

   • Result: If excess NaOH is added, the precipitate dissolves to form a colorless solution.

   • Ionic equation:

   Al³⁺ + 3OH⁻ → Al(OH)₃(s) Al(OH)₃ + OH⁻ → [Al(OH)₄]⁻

3. Test for SO₄²⁻ (Sulfate ion):

   • Test: Add BaCl₂ solution to the sample, and a white precipitate of BaSO₄ should form.

   • Result: Formation of a white precipitate confirms the presence of sulfate ions.

   • Ionic equation:

   Ba²⁺ + SO₄²⁻ → BaSO₄(s)

These tests confirm the identities of the ions present in the mineral.