A 50.00mL sample of solution containing Fe^2+ ions is titrated with a 0.0216 M KMnO4 solution. It required 20.62mL of KMnO4 solution to oxidize all the Fe^2+ ions to Fe^3+ ions by reaction.

MnO4- (aq) + Fe^2+ (aq) ------> Mn^2+ (aq) + Fe^3+ (aq) (unbalanced)
acidic

a.) What was the concentration of Fe^2+ ions in the sample solution?

b.) What volume of 0.0150 M K2Cr2O7 solution would it take to do the same titration? The reaction is
Cr2O7^2- (aq) + Fe^2+ (aq) ---------> Cr^3+ (aq) + Fe^3+ (aq) (unbalanced)
acidic