3. For an unknown solution that contains at least one of the Group I cations, answer the following questions.
(a) Upon adding 6 M HCl to the unknown solution, a white precipitate forms. What cation(s) may be present in the unknown?
(b) When the white precipitate from (a) is treated with hot water, the white precipitate remains and a colorless supernatant is observed. The supernatant is pour into a new test tube. Adding K2Cr2O4(aq) to the colorless supernatant results in no reaction. What conclusion can be made about the presence or absence of Group I cations in the unknown?
(c) When the precipitate from (b) is treated with 6 M NH3(aq), it dissolves. If HNO3 were then added to the resulting solution, what would you expect to observe? Give the balanced net ionic equation, including phase symbols, for the reaction that occurs upon addition of the HNO3.
4. A solution may contain Ag+, Pb2+, and/or Hg22+. A white precipitate forms when 6 M HCl is added. The precipitate is partially soluble in hot water. The supernatant and the precipitate are places into two separate test tubes. The solid remaining after treatment with hot water turns black on addition of 6 M NH3. The supernatant is tested with K2CrO4 and a yellow precipitate forms. No other precipitates are observed while preforming the procedure. Which of the ions are present and which are absent? State your reasoning.