Answer to Question #82650 in General Chemistry for Cheyenne Ross

Question

calculate the mass percent of the hydrogen peroxide in the old bottle. The molar mass of H2O2 is 34.0147 g/mol and the density of the solution is 1.000 g/mL

Answer 1

Hydrogen peroxide decomposes in the presence of heat, light, or other catalysts, the quality of a hydrogen peroxide solution must be checked regularly to maintain its effectiveness. The concentration of hydrogen peroxide can be analyzed by redox titration with potassium permanganate.

In this experiment, potassium permanganate will be used as the titrant to analyze the concentration of hydrogen peroxide in a commercial antiseptic solution. The permanganate ion acts as an oxidizing agent - it causes the oxidation of hydrogen peroxide. The oxidation half-reaction shows that two electrons are lost per molecule of hydrogen peroxide that is oxidized to oxygen gas. The permanganate ion, in turn, is reduced from the +7 oxidation state in MnO4- to the +2 oxidation state in Mn2+. The reduction half-reaction shows a gain of five electrons.

H2O2(aq) → O2(g) + 2H+(aq) + 2e-

MnO-4(aq) + 8H+(aq) + 5e- →Mn2+(aq) + 4H2O(l)

Standard potassium permanganate solution will be added via buret to the hydrogen peroxide solution. As the dark purple solution is added, it will react with the hydrogen peroxide and the color will fade. When all of the hydrogen peroxide has been used up, the "last drop" of potassium permanganate that is added will keep its color. The endpoint of the titration is the point at which the last drop of potassium permanganate added to the solution causes it to turn pink.

So to calculate the mass percent of the hydrogen peroxide in the old bottle, we must have the volume of solution and determine molar concentration of H2O2.