A particular solution may contains any of the the following ions: Ni2+, Cr3+, Pb

Question

A particular solution may contains any of the the following ions: Ni2+, Cr3+, Pb2+, Ca2+, Cu2+, Na1+. On addition of dilute HCl, no precipitate forms. The pH is adjusted to about 1 and H2S is bubbled in; a precipitate forms. After filtering off this precipitate, the pH is adjusted to 8 and (NH4)2S is again added; a precipitate forms. After the precipitate is filtered off, no precipitate forms upon addition of (NH4)2HPO4. Based on these observations, which of the possible ions might be present, which are definitely present, and which are definitely absent in the solid.

Explanation / Answer

No Cl- precipitates

Pb+2 is NOT present

for H2S in acidic solution, possibility: Cu+2 ion...

for H2S in basic solution, possibility: Ni+2 ion...

Addition of HPO4... No Ca+2

so

Na+ could be present since it wont precipitate

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