|MadSci Network: Chemistry|
Linzi, Sorry for the lateness of the answer. Altough I'm not sure what is meant by "vol" as in 5 vol, I think that by increasing the concentration of H202 above a certain level (which you may not yet have reached)you will completely inactivate the yeast, which would not give you much information. I'm guessing that you'd need an amount of KMnO4 roughly equivalent to the amount of H202 added. You might want to try a very dilute solution of KMnO4 (such as 0.01M) to allow you to do the titration accurately.
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