Question

`HgCl_(2)` and `I_(2)` both when dissolved in water containing `I^(-)` ions the pair of species formed is:
A. `HgI_(2), I_(3)^(-)`
B. `HgI_(2),I^(-)`
C. `HgI_(2)^(2-),I_(3)^(-)`
D. `Hg_(2)I_(2),I^(-)`

Answer 1

Correct Answer - C
In a solution containing `HgCl_(2), I_(2) and I^(-)`, both `HgCl_(2)` and `I_(2)` compete for `I^(-)` .
Since formation constant of `[HgI_(4)]^(2-) "is" 1.9xx10^(30)` which is very large as compared with `I_(3)^(-)(K_(f)=700)`
`:.` `I^(-)` will preferentially combine with `HgCl_(2)` .
`HgCl_(2) +2I^(-) to underset("Red ppt")(HgI_(2) darr)+2Cl^(-)`
`HgI_(2)+2I^(-) to underset("soluble")([HgI_(4)]^(2-))`