Question

An unknown molybdate (MoO4^-2) solution (50.00ml) was passed through a column containing Zn(s) to convert molybdate into Mo^3+. One mole of MoO4^-2 gives one mole of Mo^3+. The resulting sample required 22.11 ml of 0.01234 M KMnO4 to reach a purple end point from the reaction

3MnO4^- + 5Mo3+ + 4H^+ --> 3Mn^2+ + 5MoO2^2+ + 2H2O

A blank required 0.07ml. Find the molarity of molybdate in the unknown.

The answer is supposed to be 9.066mM, but of course I need help understanding how to get this answer.

Answer 1

moles MnO4^- used = M x L = ?
(Don't forget to subtract 0.07 from 22.11 mL)
Using the coefficients in the balanced equation, convert moles MnO4^- to moles Mo^3+.
M MoO4^2- = moles/L soln, then convert to mM by multiplying by 1000.