We doing this as a high school project of BOD on pond water and are following a video method (https://www.youtube.com/watch?v=QZXlIbeGWA0) we found on the internet and we get a pale brown ppt after the sodium iodide azide, but then we add the concentrated H2SO4 and after we mix it, it goes colorles like water so we can't do any titration. Can anyone help please?
In the BOD titration process, manganese sulfate, sodium iodide azide, and concentrated sulfuric acid are added to fix the dissolved oxygen in the water sample. The dissolved oxygen reacts with manganese sulfate to form a brownish-orange precipitate. The addition of sodium iodide azide reagent further reacts with the dissolved oxygen to form iodine. The iodine then reacts with manganese sulfate to form a brownish-black precipitate. Finally, concentrated sulfuric acid is added to dissolve the precipitate and release iodine.
If the solution goes colorless after adding these reagents, it could be due to several reasons. One possibility is that no dissolved oxygen was present in the water sample. Another option is that the sample needed to be mixed better after adding the reagents, which could have resulted in an incomplete reaction. It’s also possible that there was an error in measuring or adding one of the reagents, which could have affected the reaction.
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