Question

A solution is present in a test tube, but the test tube is not labeled. It could be Zn²⁺ or Mn²⁺. What reagent could you add to the solution to determine what it contains? Describe what will happen to the solution when the reagent is added if the solution contains Zn²⁺ and what will happen if it contains Mn²⁺.

Answer 1

Test for Mn2+

Take 10 drops of this solution, add 1 mL of conc. HNO₃., now add excess solid sodium bismuthate (NaBiO₃) and stir well. Now wait about 1 minute and then centrifuge the mixture. This solution will give purple due to the formation of MnO₄^-.

Test for Zn2+

Take 10 drops of this solution, add 1 mL of conc. NH₃(aq) to give a neutral pH. Then make the solution slightly acidic to litmus paper with 6 M HCl. After make solution acidic add 1 or 2 drops 0.5 M K₄Fe(CN)₆ and stir. A gray-white precipitate of K₂Zn[Fe(CN)₆]₂ is formed.