Take three test tubes, add a certain amount of the above three solutions respectively, and drop a few drops of NaOH solution into the three test tubes, and the test tubes with black precipitate are filled with silver ion solution (2Ag+2OH-= = Ag2O black+H2O); The test tube with white precipitate is filled with zinc ion solution (Zn2++2OH-= = Zn (0h) 2White); The test tube with green precipitate is filled with nickel ion solution (Ni2++2OH- == Ni(0H)2 green).
(2) Separation of silver ions, divalent zinc ions and divalent nickel ions
Put the mixed solution containing three cations into an appropriate container, and add 0.3 mol/L H2S solution containing HCl. In this strongly acidic solution, only Ag2S with extremely small Ksp will precipitate, and Zn2+ and Ni2+ will not generate sulfide precipitate (2Ag++S2- == Ag2S), and filtrate (containing Zn2+ and Ni2+) and Ag2S precipitate will be obtained by filtration. In addition, when enough NaOH solution is added to the filtrate, Ni2+ precipitates in the form of Ni(OH)2 and Zn2+ remains in the filtrate in the form of Zn(OH)42- due to the amphoteric nature of zinc hydroxide and the alkalinity of nickel hydroxide. Filtering the precipitate and adding dilute hydrochloric acid to obtain Ni2+; Acidizing the filtrate to obtain Zn2+