Iron(II) can be oxidized by an acidic K2Cr2O7 solution according to the net ionic equation: Cr2O72− + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ + 7H2O If it takes 35.5 mL of 0.0250 M K2Cr2O7 to titrate 25.0 mL of a solution containing Fe2+, what is the molar concentration of Fe2+ in the original solution?

The molar concentration of Fe²⁺ in the original solution is 1.33 molar

Explanation:

Moles of K₂Cr₂O₇ = Molarity x Volume (lit)

                             = 0.025 x 35.5 x 10⁻³

                             = 0.0008875

Cr₂O₇²⁻ + 6 Fe²⁺ + 14 H⁺ → 2 Cr³⁺ + 6 Fe³⁺ + 7 H₂O

From equation

              1 mole K₂Cr₂O₇ used for the oxidation of 6 moles Fe²

0.0008875 mole K₂Cr₂O₇ used for the oxidation of = = 0.005325 mole of  Fe²

      Molarity =

Molar concentration of  Fe² = = 1.33 molar

So molar concentration of Fe²⁺ in the original solution = 1.33 molar