Characteristics of Ammonia

1. Ammonia gas can turn a moist red litmus paper to blue.
2. As an alkali, ammonia can react with acid to form salt and water.
   Example
   H₂SO₄(aq) + 2NH₃(aq) → (NH₄)₂SO₄(aq)
   HNO₃(aq) + NH₃(aq) → NH₄NO₃(aq)
   H₃PO4(aq) + 3NH₃(aq) → (NH₄)₃PO₄(aq)
3. Ammonia dissolve into water to form ammonium and hydroxide ion.
   NH₃ + H₂O→ NH₄⁺ + OH^–
4. The hydroxide ion can react with many kinds of positive ion to form precipitate.
   Example
   Mg²⁺ + 2OH^– → Mg(OH)₂
   Fe²⁺ + 2OH^– → Fe(OH)₂
   Al³⁺ + 3OH^– → Al(OH)₂

Testing for Ammonia

1. Ammonia is the only common alkaline gas so it can be identified with moist red litmus paper turning blue.
2. Concentrated ammonia when reacts with concentrated hydrochloric acid produces white fume.
   Ammonia gas + Hydrogen chloride gas → ammonium chloride
   NH₃ (g) + HC1 (g) → NH₄C1