When H_(2)S gas is passed through aqueous solution of CuCl_(2), HgCl_(2), BiCl_(3) and CoCl_(2) in the presence of excess of dilute HCl, it fails to precipitate

When H_(2)S gas is passed through aqueous solution of CuCl_(2), HgCl_(

1.	When H_(2)S gas is passed through aqueous solution of CuCl_(2), HgCl_(2), BiCl_(3) and CoCl_(2) in the presence of excess of dilute HCl, it fails to precipitate
Answer» `CuS` `HgS` `Bi_(2)S_(3)` `COS` SOLUTION :The `k_(sp)` of CoS is QUITE high. In acidic medium, `S^(2-)` ion concentration gets suppressed. The concentration of `Co^(2+)` and `S^(2-)` ions REMAIN less than the `k_(sp)` VALUE of the salt. Therefore, CoS is not precipitated.