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Amphoteric Hydroxides

Why do the amphoteric hydroxides form on addition of a little NaOH(aq), but dissolve in excess, to give a solution?

Cr3+ forms green-blue ppt, then a green solution.
Al3+ forms a white ppt, then a colourless solution.
Zn2+ forms a white ppt, then a colourless solution.

Any information would be greatly appreciated.
Original post by Jglover653
Why do the amphoteric hydroxides form on addition of a little NaOH(aq), but dissolve in excess, to give a solution?

Cr3+ forms green-blue ppt, then a green solution.
Al3+ forms a white ppt, then a colourless solution.
Zn2+ forms a white ppt, then a colourless solution.

Any information would be greatly appreciated.


The high charge density of the ion helps polarise the water molecule ligands.

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