Chemical amounts (A2)
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I am doing an A2 Chemistry planning exercise to determine the % purity of iron in a sample of cast iron by a redox titration. I know the cast iron should first be dissolved in sulphuric acid, but I do not know how to prevent the further oxidation of ferrous sulphate, or how to determine whether all the iron has all dissolved. Is it when there are no more gas bubbles? Do I need to write it as a complex ion, Fe(H2O)6SO4, when I write the equation of it with KMnO4? If not, then how should I write it? Thank you very much.
Igloo writes ...
To determine whether the iron has all dissolved, it is probably best to wait until no more gas bubbles are evolved.
There is probably no need to worry about any further oxidation of iron(II) to iron(III) ions, since in acidic solution aerial oxidation does not readily take place. This is one reason why you should always use an excess of sulphuric acid during the dissolving process.
When writing the equation for the reaction occurring during subsequent titration process I would recommend that you use an ionic equation:
i.e. …..Fe2+(aq) + …..MnO4-(aq) + …..H+(aq) ----> …………………………….
I’ll leave you to balance this equation.
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updated: 17 December 2006
