# Which metal ions precipitate in NH4OH? [closed]

From Wikipedia-1, and from an answer here on Stack-Exchange, I can list at least the following elements which will dissolve in aqueous $$\ce{NH4OH}$$:

• $$\ce{Cr(III), Co(III), Ni(II), Cu(I, II), Zn(II), Ag(I),}$$ along with "several platinum group metals"

From reading Wikipedia-2, I also suspect the following elements to dissolve in liquid ammonia:

• $$\ce{Mg, Ca, Sr, Ba, Eu, Yb, Li, Na, K}$$ and $$\ce{Rb}$$

As a matter of fact, according to Wikipedia "almost all metal ions bind ammonia as a ligand." I thought it would be interesting, and potentially very useful, to find out which metal ions are NOT soluble in $$\ce{NH4OH}$$.

I can list two for now:

• $$\ce{Fe(OH)3}$$
• $$\ce{Mg(OH)2}$$ with a solubility product of only $$5.61×10^{−12}$$ (credit to Oscar Lanzi)

## closed as unclear what you're asking by Mithoron, Buttonwood, airhuff, Jon Custer, TyberiusJul 29 at 16:58

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• There is a huge difference in pure liquid $\ce{NH3}$ and an aqueous solution of $\ce{NH4OH}$. I can't imagine any of the metals Mg, Ca, Sr, Ba, Li, Na, K or Rb forming amine complexes. – MaxW Jul 11 at 0:34

For the case of magnesium ion, at least, it seems a stretch to say it dissolves in ammonia solution. Assume that the ammonia solution has $$\mathrm{pH}$$ of $$11$$ and magnesium hydroxide has a solubility product of $$5.61×10^{-12}$$. We infer that the magnesium ion solubility at equilibrium with the hydroxide in ammonia solution is only $$\pu{5.6μM}$$ which is not really all that soluble.