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How to determine the purity ?

發問:

How to determine the purity od a sample of hydrated iron(II) sulphate crystals? Standardised potassium permanganate solution is provided

最佳解答:

first, weigth x gram of the sample of hydrated iron(II) sulphate crystals then, dissolve them with L ml water. titrate potassium permanganate solution against the solution then find out amount of potassium permanganate solution used By, 1 x 8H+ + MnO4- + 5e- --> Mn2+ + 4H20 5 x Fe3+ + e- -> Fe2+ then find out the no of mole of used potassium permanganate the find out the no of mole of iron(ii) sulphate in x gram calculate the molar mass comapare it with standard value

其他解答:

This is a difficult test, Hydrated iron(II) sulphate crystals is very easily oxidized, so even though the chemical is freshly bought, some Fe2+ had changed to Fe3+. So you must assume that no Fe3+ present in sample Dissolve suitable amount Fe2+ in dilute sulphuric acid, not distilled water, oxygen in water will change Fe2+ to Fe3+., then titrate with standardized KMnO4.
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