Question

Suppose you did a cation group I analysis and treated the chloride precipitate with ${NH}_3\left(aq\right)$, without first trating it with hot water. What might you observe and what valid conclusions could you reach about cations present, cations absent, and cations in doubt?

Answer 1

If ${Hg}_2{Cl}_2,AgCland{PbCl}_2$ are precipitated then,
(a) ${PbCl}_2$ remains insoluble
(b) ${Hg}_2{Cl}_2$ is blackened by addition of ${NH}_3$ due to formation of ($Hg+{HgNH}_{2}Cl$)
$H{g}_{2}C{l}_2+2N{H}_{4}OH\to Hg+{HgNH}_{2}Cl+N{H}_{4}Cl+H_{2}O$
(c) $AgCl$ goes into solution as soluble complex $\left[{Ag\left({NH}_3\right)}_2\right]Cl$
$AgCl+2N{H}_3\to \left[Ag\right(N{H}_3{)}_2]Cl$