Gce Model Questions Vol1 2019 Chemistry Question 11

Potassium dichromate (\(\mathrm{K_2Cr_2O_7}\)) is used to oxidise ferrous ions in acidic solution according to the half‑reaction \(\mathrm{Cr_2O_7^{2-} + 6 Fe^{2+} + 14 H^{+} \rightarrow 2 Cr^{3+} + 6 Fe^{3+} + 7 H_2O}\). A sample of \(0.250\ \text{g}\) of anhydrous \(\mathrm{K_2Cr_2O_7}\) is dissolved in excess acid and mixed with an unknown concentration of \(\mathrm{Fe^{2+}}\) solution. After the reaction, \(10.0\ \text{cm}^3\) of the remaining \(\mathrm{Fe^{2+}}\) solution is titrated with \(0.0200\ \text{M}\) potassium permanganate (\(\mathrm{KMnO_4}\)). The titration requires \(15.0\ \text{cm}^3\) of the permanganate solution. The original volume of the \(\mathrm{Fe^{2+}}\) solution was \(100.0\ \text{cm}^3\). Calculate the initial molarity of the \(\mathrm{Fe^{2+}}\) solution.