Chemistry
State how NH4OH is used for identifying:
- Fe2+
- Fe3+
- Pb2+
- Zn2+
- Cu2+ cations.
Give also a balanced equation in each case for a known example.
Answer
A soln. of Fe2+ ions gives dirty green ppt. which is insoluble in excess of NH4OH.
FeSO4 + 2NH4OH ⟶ (NH4)2SO4+ Fe(OH)2 ↓A soln. of Fe3+ ions gives reddish brown ppt. which is insoluble in excess of NH4OH
FeCl3 + 3NH4OH ⟶ 3NH4Cl + Fe(OH)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 ↓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 + 4H2OA 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
Related Questions
State why an aqueous solution of ammonia (NH4OH) is used for identifying cations.
Give balanced equations for the reducing reactions of ammonia with
(i) copper (II) oxide,
(ii) lead (II) oxide,
(iii) chlorine using (a) excess NH3 (b) excess Cl2
State a reason why reaction of liquor ammonia with nitric acid is a neutralization reaction.
State why the blue ppt. formed on addition of NH4OH to CuSO4 soln. dissolves to give a deep blue solution with excess of NH4OH. Give an equation for the reaction. State why Zn(OH)2 is soluble in excess of NH4OH.