What transition metal has a white precipitate when reacted with sodium hydroxide?

Answer 1

unobtainium

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That is highly dependent on the cluster size of the transition metal.

For example:

a) Dissolve gold in aqua regia, this will create gold clusters of some hundred to some thousand gold atoms. If you precipitate it with NaOh the precipitate is brown.

b) Dissolve gold in aqua regia, get rid of the nitric acid by repeated evaporation with HCl - Boil the solution a long time in HCl - You will end up with Au2Cl6 - This will form a orangish red precipitate...

c) Dissolve gold in aqua regia, get rid of the nitric acid by repeated evaporation with HCl - Boil the solution a long time in HCl and NaCl (1 mol of gold to 20 mol of NaCl) - The color of the gold clorid will turn green and you will end up with NaAuCl3 - Use nitric acid to get rid of the clorid - you end up with NaAu - raise the ph to exact 7 (with NaOH)and you will end up with HAu which forms a white precipitate - anneal the HAu ander innert gas to get pure monoatomic Au a white powder.

Fazit: the world of microclusters is strange...