[robertss]

http://www.files.chem.vt.edu/RVGS/ACT/lab/Experiments/Exp_2-peroxide_97.html

We completed this lab using 3% hydrogen peroxide. Our data showed that it was actually around 2.4% H202.

I know that if the hydrogen peroxide had been sitting on the shelf for a long time, its decomposition reaction is spontaneous and it would become a lower percent h202.
I also know that H202 decomposes in light. So while we were doing the lab, the hydrogen peroxide may have decomposed a bit.

But what are possible experimental sources of error?
The lab notes that "a brown ppt will sometimes form, especially if the KMnO4 solution is not stirred as it is added". How does not stirring affect the calculated % of hydrogen peroxide?

I'm trying to figure out errors I may have done in procedure that would have decreased the calculated percentage of H202.


Also, would adding insufficient acid increase or decrease the concentration of H202.
Another website noted that "If an insufficient amount of acid is added in step nine, some of the permanganate ions will be
reduced to MnO2 instead of Mn2+."
What does that do to the concentration?

Thanks so much!