Sodium ethanedioate is used to find the concentration of solutions of potassium manganate(VII) by titration. The equation for this reaction is:
2MnO4−+16H++5C2O42−→2Mn2++8H2O+10CO2 2\text{MnO}_4^- + 16\text{H}^+ + 5\text{C}_2\text{O}_4^{2-} \rightarrow 2\text{Mn}^{2+} + 8\text{H}_2\text{O} + 10\text{CO}_2 2MnO4−+16H++5C2O42−→2Mn2++8H2O+10CO2A standard solution is made by dissolving 215 mg of Na2C2O4\text{Na}_2\text{C}_2\text{O}_4Na2C2O4 (Mr=134.0M_r = 134.0Mr=134.0) in water and making up to 250 cm3 in a volumetric flask.
25.0 cm3 of this solution and an excess of sulfuric acid are added to a conical flask. The mixture is warmed and titrated with potassium manganate(VII) solution. The titration is repeated until concordant results are obtained. The mean titre is 19.65 cm3.
Calculate the concentration, in mol dm−3\text{mol dm}^{-3}mol dm−3, of the potassium manganate(VII) solution. Give your answer to 3 significant figures.
79 exam-style questions on AQA A Level Chemistry Amount of substance, covering Relative atomic mass and relative molecular mass, The mole and the Avogadro constant, The ideal gas equation, Empirical and molecular formula, and Balanced equations and associated calculations. Each one has a worked solution and a mark scheme showing where the marks go.