An iron ore sample was dissolved in acid and all the iron converted to Fe2+(aq)\text{Fe}^{2+}(aq)Fe2+(aq) ions. A 25.00 cm3 sample of this Fe2+(aq)\text{Fe}^{2+}(aq)Fe2+(aq) solution was titrated against a standard solution of potassium dichromate(VI), K2Cr2O7\text{K}_2\text{Cr}_2\text{O}_7K2Cr2O7. The complete oxidation of Fe2+(aq)\text{Fe}^{2+}(aq)Fe2+(aq) required 20.00 cm3 of 0.0150 mol dm-3 K2Cr2O7(aq)\text{K}_2\text{Cr}_2\text{O}_7(aq)K2Cr2O7(aq) according to the equation below:
Cr2O72−(aq)+14H+(aq)+6Fe2+(aq)⟶2Cr3+(aq)+6Fe3+(aq)+7H2O(l) \text{Cr}_2\text{O}_7^{2-}(aq) + 14\text{H}^+(aq) + 6\text{Fe}^{2+}(aq) \longrightarrow 2\text{Cr}^{3+}(aq) + 6\text{Fe}^{3+}(aq) + 7\text{H}_2\text{O}(l) Cr2O72−(aq)+14H+(aq)+6Fe2+(aq)⟶2Cr3+(aq)+6Fe3+(aq)+7H2O(l)What is the concentration of Fe2+(aq)\text{Fe}^{2+}(aq)Fe2+(aq), in mol dm−3\text{mol dm}^{-3}mol dm−3, in the sample?
0.01200.01200.0120
0.07200.07200.0720
0.1130.1130.113
0.002000.002000.00200
