Qualitative analysis of cobalt II salts

Qualitative analysis of cobalt II salts

Qualitative analysis of cobalt II salts

Common salt: Cobalt sulphate: CoSO4

(a)With dilute sodium hydroxide solution of ammonium solution

Observation

Blue precipitate insoluble in excess turns brown on standing

Confirmatory test

(a) Forms deep blue solution with concentrated hydrochloric acid.

Co(H2O)62+ (aq) + 4Cl (aq) → CoCl42- (aq) + 6H2O (l)

(b) With Concentrated ammonia forms a blue precipitate soluble in excess to give pale yellow solution; the solution turns brown on standing.

[Co(H2O)6]2+ (aq) + 2OH (aq)   → Co(OH)2 (s)

pink                                                      blue ppt

Co(OH)2 (s) + 6NH3 (aq) s → [Co(NH3)6]2+(aq)

red-brown

[Co(NH3)6]2+(aq) →Co(NH3)6]3+(aq) +e

red-brown                 yellow solution

 

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