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ICSE Class 10 Chemistry Question 23 of 69

Study of Compounds — Ammonia — Question 19

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Question 19

Distinguish between the following pairs of compounds using the test given in bracket :

(a) Iron [II] sulphate and iron [III] sulphate [using ammonium hydroxide]

(b) A lead salt and a zinc salt [using excess ammonium hydroxide]

Answer

(a) On reaction with ammonium hydroxide, Iron [II] sulphate forms a dirty green ppt whereas iron [III] sulphate forms a reddish brown ppt. Hence, the two can be distinguished easily.

FeSO4 + 2NH4OH ⟶ (NH4)2SO4 + Fe(OH)2 ↓

Fe2(SO4)3 + 6NH4OH ⟶ 3(NH4)2SO4 + 2Fe(OH)3 ↓

(b) A lead salt gives a chalky white ppt. on reaction with ammonium hydroxide that is insoluble in excess of ammonium hydroxide.

Pb(NO3)2 + 2NH4OH ⟶ 2NH4NO3 + Pb(OH)2 ↓

On the other hand, zinc salt forms a white gelatinous ppt. which dissolves when excess of ammonium hydroxide is added. Hence, the two can be distinguished.

ZnSO4 + 2NH4OH ⟶ (NH4)2SO4 + Zn(OH)2 ↓

[Zn(OH)2] + (NH4)2SO4 + 2NH4OH ⟶ [Zn(NH3)4]SO4 + 4H2O