Hydrated iron(II) sulfate (FeSO4⋅7H2O\text{FeSO}_4\cdot 7\text{H}_2\text{O}FeSO4⋅7H2O) is used to find the concentration of solutions of potassium dichromate(VI) by titration. The equation for this reaction is:
Cr2O72−+14H++6Fe2+→2Cr3++6Fe3++7H2O \text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6\text{Fe}^{2+} \rightarrow 2\text{Cr}^{3+} + 6\text{Fe}^{3+} + 7\text{H}_2\text{O} Cr2O72−+14H++6Fe2+→2Cr3++6Fe3++7H2OA standard solution is made by dissolving 1390 mg1390\text{ mg}1390 mg of FeSO4⋅7H2O\text{FeSO}_4\cdot 7\text{H}_2\text{O}FeSO4⋅7H2O (Mr=278.0M_r = 278.0Mr=278.0) in dilute sulfuric acid and making up to 250 cm3250\text{ cm}^3250 cm3 with distilled water in a volumetric flask.
25.0 cm325.0\text{ cm}^325.0 cm3 of this solution is pipetted into a conical flask and titrated with potassium dichromate(VI) solution. The titration is repeated until concordant results are obtained. The mean titre is 22.45 cm322.45\text{ cm}^322.45 cm3.
Calculate the concentration, in mol dm−3\text{mol dm}^{-3}mol dm−3, of the potassium dichromate(VI) solution. Give your answer to 3 significant figures.
