| MadSci Network: Chemistry |
Jessi-- There are several varieties of the Winkler method; I found the chemical reactions for one variant, which is called the Alsterberg-azide modification. This method forms a precipitate of manganous hydroxide, which absorbs dissolved oxygen, and then uses iodine to measure the amount. The explanation comes from an old version of the U.S. Geological Survey's "Methods for determination of inorganic substances in water and fluvial sediments, book 5, chapter A1." I know it was published after 1976, but the page with the publication date is missing. Here are the equations: MnSO4 + 2KOH --> Mn(OH)2ppt + K2SO4 2Mn(OH)2ppt + O2 --> 2MnO(OH)2ppt Then you acidify the mixture with iodine, which is released in a quantity equivalent to the dissolved Oxygen present: MnO(OH)2ppt + 2KI + H2O -->(with H+) Mn(OH)2ppt + I2 + 2KOH Titrate the iodine with sodium thiosulfate standard solution with use of starch indicator: I2 + 2S2O3-2 --> S4O6-2 + 2I-1 The book cites this reference: Adams, R. C., Barnett, R. D., and Keller, D. E., Jr., 1943, Field and laboratory determination of dissolved oxygen: American Society for Testing and Materials, Proc. 43. I hope this information helps you out. If you have any more questions, please do not hesitate to ask. Sincerely, David C. Kopaska-Merkel Geological Survey of Alabama PO Box O, Tuscaloosa AL 35486 (205) 349-2852 Email: davidkm@ogb.gsa.tuscaloosa.al.us
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