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ICSE Class 10 Chemistry Question 6 of 69

Study of Compounds — Ammonia — Question 23

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Question

Question 23

State how NH4OH is used for identifying:

  1. Fe2+
  2. Fe3+
  3. Pb2+
  4. Zn2+
  5. Cu2+ cations.

Give also a balanced equation in each case for a known example.

Answer

  1. A soln. of Fe2+ ions gives dirty green ppt. which is insoluble in excess of NH4OH.
    FeSO4 + 2NH4OH ⟶ (NH4)2SO4+ Fe(OH)2 ↓

  2. A soln. of Fe3+ ions gives reddish brown ppt. which is insoluble in excess of NH4OH
    FeCl3 + 3NH4OH ⟶ 3NH4Cl + Fe(OH)3 ↓

  3. A soln. of Pb2+ ions gives chalky white ppt. which is insoluble in excess of NH4OH
    Pb(NO3)2 + 2NH4OH ⟶ 2NH4NO3 + Pb(OH)2 ↓

  4. A soln. of Zn2+ ions gives gelatinous white ppt. which is soluble in excess of NH4OH
    ZnSO4 + 2NH4OH ⟶ (NH4)2SO4 + Zn(OH)2 ↓
    Zn(OH)2 + (NH4)2SO4 + 2NH4OH ⟶ [Zn(NH3)4]SO4 + 4H2O

  5. A soln. of Cu2+ ions gives pale blue ppt. which is soluble in excess of NH4OH
    CuSO4 + 2NH4OH ⟶ (NH4)2SO4 + Cu(OH)2 ↓
    Cu(OH)2 + (NH4)2SO4 + 2NH4OH ⟶ [Cu(NH3)4]SO4 + 4H2O