Search: Permanganat

Manganese ions are catalytically oxidized into purple-colored permanganate ions. The purple color of the solution is determined using a comparator (or photometrically):

Mn²⁺ + 12  H₂O → MnO₄^- + 8 H₃O⁺ + 5 e^-

Potassium permanganate oxidizes many organic and certain inorganic substances more or less completely in acidic, neutral or alkaline solutions. The volume of potassium permanganate required in the analysis is determined potentiometrically. Since oxidation depends on the type of solution, on its temperature and on the reaction time, the procedure described below must be followed precisely.

In acidic solutions, permanganate ions are typically reduced to manganese(II) ions:

MnO₄^- + 5 e- + 8 H₃O⁺ → Mn²⁺ + 12 H₂O

In alkaline solutions, the reduction results in tetravalent manganese only:

MnO₄^- + 3 e- + 4 H₃O⁺ → MnO₂ + 6 H₂O

Since in both cases the titration takes place in an acidic solution, this is irrelevant for the calculation. By adding oxalic acid, both the excess permanganate ions as well as the tetravalent manganese are reduced to manganese(II) ions:

2 MnO₄^- + 5 C₂O₄^2- + 16 H₃O⁺ → 2 Mn²⁺ + 24 H₂O + 10 CO₂

MnO₂ + C₂O₄²- + 4 H₃O⁺ → Mn²⁺ + 6 H₂O + 2 CO₂  

The quantitative determination is carried out in a sulphuric acid solution by titration with potassium permanganate:

5 H₂0₂ +  2  KMnO₄ + 3  H₂S0₄  →  2 MnSO₄ + H₂S0₄ + 8 H₂0 + 5 0₂

If the sample contains other peroxide-containing disinfectants in addition to hydrogen peroxide (H₂O₂), the method T-754-01-032 Peracetic-acid-based-disinfectants must be used.