6. A student did experiment 1 and saw the following results.
Upon adding HCl to the unknown mixture, there was a white
precipitate. Then upon addition of the ammonia solution, there was
no precipitate. When (NH4)2C2O4 is added, a white precipitate
forms. Nitric acid is added to the solution, and this is dried. The
residue is reconstituted in a hydrochloric acid solution, and then
sodium hydroxide is added. Upon heating a precipitate forms. The
solution turns yellow upon addition of Na3Co(NO2)6. What cations
are present in the unknown?