Redox and redox equilibria
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Where can I find out about the reactions between potassium manganate(VII) and iron(II) oxalate. This is for an experiment investigation the iron(II) content of different vegetables using a titration with patassium manganate(VII).
These three points may help you.
(1) Potassium manganate(VII) oxidises iron(II) ions at room temperature in the presence of acid. Manganese changes from the +7 to the + 2 state while iron changes from +2 to +3. So 1 mol manganate(VII) oxidises 5 mol iron(II). You will find the equations in any standard chemistry text.
(2) Potassium manganate(VII) in acid oxidises oxalate (ethanedioate) ions to carbon dioxide but only on heating. The reaction at room temperature is too slow for a titration. Once the titration has started at about 60 degrees it then goes much faster because Mn(II) ions formed act as a catalyst for the reaction. 5 mol oxalate ion react with 2 mol manangate(VII). Again you will find the equations in any standard A-level textbook.
(3) So if you titrate material containing iron(II) oxalate you will get a different result at room temperature from the result you get on heating.
(4) The formula of iron(II) oxalate is FeC2O4•nH2O
Overall, on titrating a hot solution of the salt, 5 mol iron(II) oxalate reacts with 3 mol manganate(VII). You can use the result of a titration to find the value of 'n'.
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updated: 05 January 2004
