Video: Complexation of the nickel(II) ion
Addition of ammonia to the green hexaaquanickel(II) ion results in the formation of the blue hexaamminenickel(II) ion.[Ni(OH2)6]2+(aq) + 6 NH3(aq) ® [Ni(NH3)6]2+(aq) + 6 H2O(l)
At the interface, a pale blue precipitate can be seen. This is a result of the reaction between the nickel(II) ion and the hydroxide ion from the hydrolysis of the ammonia (i.e., the solution is basic):
NH3(aq) + H2O(l) ? NH4+(aq) + OH-(aq)
Ni2+(aq) + 2 OH-(aq) ? Ni(OH)2(s)