[Catalist] One for the Chemists

[Andrew Bland]

Hi all, please check if you agree with this model answer, from a validation after a redox titration, permanganate + hydrogen peroxide. Thanks, Andrew.




Q: If insufficient acid is added in step 9, some of the permanganate ions will react to form MnO2 instead of Mn2+. The equation for this reaction is:


                                            2 MnO4- + 3H2O2 + 2H+  --> 2MnO2 + 4H2O +3O2

The original equation is:
                            2MnO4- + 5H2O2 + 6H+ --> 5O2 + 2Mn2+ +8 H2O





a. How would this affect the volume of KMnO4 used to reach the end point? (Would it be more or less). Explain why.


A: In the original reaction, 2 mol of MnO4- will react with 5 mol of H2O2. In the new reaction, 2 mol of MnO4- will react with 3 mol of H2O2, meaning that more MnO4- would be required to react with the same amount of H2O2 to reach the end point.
The result would be that the concentration of H2O2 would be over estimated.




Andrew Bland
Teacher

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