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4. For a solution containing at least one of the cat- ions involved in this experiment, answer the following questions. (1) A solution is acidified to pH 0.5, and H₂S is added. A dark precipitate results. Which cation(s) may be present? (2) KOH is added to the precipitate from (1). The supernatant liquid is separated from the dark precipitate and tested with HCI/H₂S. A colorless solu- tion results, with no precipitate. Which cation(s) may be present? (3) The remaining precipitate from (1) is treated with dilute HCI. The supernatant liquid is tested with NH3 and H₂S. A yellow precipitate results. Which cat- ion(s) may be present? (4) The precipitate left from the first step in (3) is dissolved in HNO3, and the resulting supernatant liq- uid is treated with NH3. A blue supernatant liquid re- sults, with no precipitate. Give the identity of all Group II cations present in the original solution.

supernatant liquid Discard if only Group II ions are present. Retain if Group III & IV ions are present. supernatant liquid 6M HCI H₂S Sn(OH)²- SnS₂ (yellow) Bi³, Cd, Cu²+, SnCl²- (centrifugation) H2S, DH 0.5 Bi₂S₂. (black) (centrifugation) Cds, CuS, (yellow- (black- orange) brown) 3M KOH supernatant liquid (CaCl), HS (colorless) Cas (yellow) residue residue CdS, BigS₂, Cus (yellow) (black) (black) (centrifugation and decantation) [Cu(NH+ (dark blue) supernatant liquid EM NH3 H₂S SnS₂ (yellow) 6MHCI residue BigS₂, Cus (black) (black) supernatant liquid B, Cu(H₂O). (blue) (centrifugation and decantation) (decantation) EM NH3 6M HNO₂ (heat) residue S (yellow) residue Bi(OH) (white)