Answer to Question #82655 in General Chemistry for Ross

Question

How many moles of 0.2 M KMnO4 were necessary to cause the color change to occur with the old H2O2 solution? Choose the closest answer.
a) 0.00252mol
b)0.0126mol
c)0.213mol
d)2.524mol

Answer 1

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 amount of moles of 0.2 M KMnO4, we must have the volume of solution and molar concentration of H2O2. Without data, it's not possible to give a specific answer.