The method describes how to determine the content of oxidizable organic substances in water using an oxidizing agent, potassium dichromate.
Water intended for use as an ingredient in the production of beer (brewing liquor) or other foods
The oxidative capacity provides information regarding the amount of oxidizable, organic matter in water. Oxidizable, inorganic matter can also be present and must be taken into consideration for this analysis. Due to the various oxidants in the water and the specific reaction conditions, the results are not comparable in every respect.
Potassium dichromate oxidizes many organic and certain inorganic substances to various extents in an acidic solution. Since the level of oxidation depends upon the kinds of substances, the concentration of potassium dichromate, the pH of the solution, and the temperature and reaction time, the procedure described below must be followed precisely. The volume of potassium dichromate required in the analysis is determined potentiometrically. In an acidic solution, the dichromate ions are reduced to chromium(III) ions:
Cr2O72- + 6 e- + 14 H3O+ → 2 Cr3+ + 21 H2O
Dichromate ions in excess of those required are determined through titration with an ammonium iron(II) sulfate solution:
Cr2O72- + 6 Fe2+ + 14 H3O+ →2 Cr3+ + 6 Fe3+ + 21 H2O