[hkalfighter]

when Cu2+ is mixed with ammonia solution , a blue ppt is formed and it redissolves in excess ammonia because an ionic complex Cu(NH3)4 2+ (aq)  is formed . When Cu2+ is mixed with NaOH , blue ppt is formed but it doesn't redissolve in excess NaOH . I understand why it's like that
But in the reaction of Pb2+ with ammonia and NaOH , it shows reverse trend that means when Pb2+ is mixed with ammonia , white ppt is formed but doesn't redissolve in excess ammonia while with NaOH , white ppt is formed but redissolves in excess NaOH .
i don't understand the case of Pb2+ , is there any complex formed like the case of Cu2+

[Alberto_Kravina]

But in the reaction of Pb2+ with ammonia and NaOH , it shows reverse trend that means when Pb2+ is mixed with ammonia , white ppt is formed but doesn't redissolve in excess ammonia while with NaOH , white ppt is formed but redissolves in excess NaOH .

Pb(OH)₂ is amphoteric! It can react either as a base or as an acid. If excess OH^- is added to Pb(OH)₂ a soluble tetrahydroxoplumbate(II) complex forms.

Cu²⁺ is not amphoteric, as a result, it is not soluble in excess OH^-. However, it forms a soluble tetrammine complex.

[hkalfighter]

thx for your quick reply .
i didn't really know that Pb(OH)2 is amphoteric
i wonder if it's similar to BeO and Al2O3 which are also amphoteric
can u tell me other metal hydroxides that are amphoteric and the metal ions that make complex with OH- and other metals ions which behave like Cu 2+ which gives complex with NH3 ligands

[Alberto_Kravina]

Other elements that form amphoteric hydroxides Bi, V, Cr, Fe, Au, Al, As, Be, Sn, Ti, Sb
These are just some metals that form amphoteric hydroxides.

[Donaldson Tan]

It all depends on whether the cation in question can form a soluble complex with the base of interest.

eg. Pb²⁺ vs OH^- and Pb²⁺ vs NH₃. The latter pair can't form a complex.