[n0m0r3l0v3_0k]

When I was highschool i studied that Cu(OH)2 is amphoteric but now my bro say that it's not amphoteric    Someone can explain this to me plz.
I remember : Cu(OH)2 + NaOH (concentrated) -> Na[Cu(OH)]4 but he said that his teacher not agree with this

[Borek]

Cu(OH)2 + NaOH (concentrated) -> Na[Cu(OH)]4

My inorganic chemistry books confirm this reaction as occuring in hot and concentrated solutions of alkali metal hydroxides. Not much copper hydroxide dissolves this way, but some does. Unfortunately my books are in Polish so even if I will list titles they will be of no use for you (unless you are from Poland and you are in Vietnam only temporarily )

[n0m0r3l0v3_0k]

Just one more question how abt Fe(OH)3 it's also amphoteric right ? NaOH(concentrated) + Fe(OH)3 -> Na[Fe(OH)4] ? Any condition ?

[nj_bartel]

Many compounds are technically amphoteric, if you put them with a strong enough acid or base.  Most people wouldn't describe them as amphoteric though.

[Borek]

NaOH(concentrated) + Fe(OH)3 -> Na[Fe(OH)4]

Very hot, and only very small amounts.

However, there are known salts like K₂FeO₄ - Fe(VI).