The titration of 25.0 mL of an iron(II) solution required 18.0 mL of a 0.160 M solution of dichromate to reach the equivalence point. What is the molarity of the iron(II) solution?
6Fe^2+ + Cr2O7^2- + 14H^+ ==> 6Fe^3+ + 2Cr^3+ + 7H2O
millimoles Cr2O7^2- = mL x M = 18.0 x 0.160 = ? let's call it y.
Convert to moles Fe^2+ this way using the coefficients in the balanced equation.
millimoles Fe^2+ = millimoles Cr2O7^2- x (6 moles Fe^2+/1 mol Cr2O7^2-) = y*6 = z
Then M Fe^2+ = millimols/mL = z mmoles Fe^2+/25.0 mL Fe^2+ = ? M