To determine the content of H2O2 in PAA solution, I did the titration experiment of PAA with KMnO4 0.05M. Sample solution: 10mL PAA solution + 50mL deionized water+ 5mL H2SO4 1:5. Normally, the equivalence point is reached as soon as the color of the sample solution turns permanently light pink in the presence of excess of KMnO4. However, my sample changed to brown color (the titer of KMnO4 0.05M is 23mL) , that means there might be a side reaction happened or a large amount of MnO2 generated. Could you please explain this situation and advice me the solution for reducing the MnO2 amount? Thank you.
Hello Linh
Thanks for sharing your question with the RG community.
Do you have any experience with this titration method and is this the first time this glitch has occurred? The formation of manganese dioxide hydrate (most commonly abbreviated as MnO2) during titrations can have several reasons. Two common reasons are:
1. the solution is not acidified strongly enough (hence my question if you have experience with the method). You could try using 20 ml (instead of 5 ml) of diluted H2SO4, or conc. H3PO4.
2. the flask or the glassware contains impurities. Sometimes people forget that ethanol is a reducing agent and that flasks rinsed with ethanol will cause precipitation of MnO2 with KMnO4.
I wish you much success for your research.
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