Question

When the Nickel (II) ion reacts with ammonia, most students notice only a color change occurring. Some student also notice a white ppt. Write the net ionic reactions to explain what the color change is and what the ppt could be?

Answer 1

Nickel(II)-ions are precipitated by ammonia as a green gelatinous precipitate of nickel(II)hydroxide,reaction is given as

Ni²⁺ (aq) + 2 OH^- (aq) 2 Ni(OH)₂ (s) [light green]ppt

This Ni(OH)2 which dissolves forming a deep blue hexaaminenickel(II) hydroxide at excess ammonia , reaction is given as-

Ni(OH)₂ (s) + 6 NH₃ (aq) [Ni(NH₃)₆]²⁺ (aq) + 2 OH^- (aq) [deep blue]
Ni 2+(aq) +2OH-(aq) + 6NH3(aq)---> [Ni(NH₃)₆]²⁺ (aq) + 2 OH^- (aq) [deep blue]