Question

The exact concentration of H2O2 in a solution that is nominally 6% w/v H2O2 can be determined by a redox titration with MnO4 – . A 25 mL aliquot of the sample is transferred to a 250 mL volumetric flask and diluted to volume with distilled water. A 25 mL aliquot of the diluted sample is added to an Erlenmeyer flask, diluted with 200 mL of distilled water and acidified with 20 mL of 25% v/v H2SO4. The resulting solution is then titrated with standard solution of KMnO4 until a faint pink color persists for 30 s. The result is reported as %w/v H2O2.

a) Many commercially available solutions of H2O2 contain an inorganic or organic stabilizer to prevent the auto decomposition of the peroxide to H2O and O2. What effect (higher, lower, no effect) would the presence of this stabilizer have on the reported %w/v H2O2 if it also reacts with MnO4 – . Explain your answer.

b) Laboratory distilled water often contain traces of dissolved organic material that also can react with MnO4 – . Describe a simple method to correct for this potential interference

c) In this titration of H2O2 with MnO4 – , no indicator is used. Explain how the end point is detected and support your answer by writing a balanced equation.

this question is 12 points, the only piece of the question I have right now is part b which I believe is boiling it out.

Answer 1

A) The reported %w/v will increase as some amount of H2O2 is also used for elimination of stabilizer.

B) Organic matter can been removed by heating in the presence of oxidizing agents.

C) MnO4 itself acts as an indicator. As long as there is H2O2 in ther solution, the permanganate will always be reduced to a clear solution. But as soon as the hydrogen peroxide is gone the intense purple color of the permanganate will be visible.

5 H₂O₂ + 2MnO₄^- + 6H+ ==> 5O₂ + 2Mn²⁺ + 8H₂O