Question

No precipitate formed when an aqueous solution of NaCl or Na2SO4 was added to the sample solution. A precipitate formed when the sample solution was made basic with NaOH. Which ion(s) are present in the sample soluiton?

[Hg2]2+
[Ba]2+
[Mn]2+

I know that all three are not, but how do I figure out what is?

Answer 1

Hg2^+2 isn't there because it would form a ppt of Hg2Cl2 with NaCl.
Ba^+2 isn't there because it would form a ppt with Na2SO4 of BaSO4.
That only leaves one possibility.
Mn^+2 + 2OH^- ==> Mn(OH)2