Question #234185

The formula for hydrated iron(II) sulfate is FeSO4.xH2O.The value of x is a whole number between 1 and 10. It can be determined by carrying out a titration with 0.0200 mol/dm3potassium manganate(VII) (KMnO4) solution as follows:• dissolve a sample of FeSO4.xH2O in water to make 250 cm3 of solution • measure out 25.0 cm3 of this solution into a conical flask • add the KMnO4 solution using a burette until the end point is reached• record the volume of solution added • repeat the titration three more times .The table shows the results. Concordant results are those within 0.20 cm3 of each other. Select concordant results from the table. *

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Expert's answer

10FeSO4 + 2KMnO4 + 8H2SO4 = 5Fe2(SO4)3 + K2SO4 + 2MnSO4 + 8H2O

You need the number of moles of FeSO4xnH2O, which is equal to the number of moles of FeSO4. You need to determine the volume of KMnO4 needed to react with the solution (the equivalence point is reached when the purple colour won't disappear anymore, as there are no Fe2+ ions left to oxidize). Now you can calculate the number of moles of KMnO4 and then using the equation you can find out the amount of FeSO4 in the solution. As you have diluted the original solution you have to do some additional calculations to determine the amount of Fe2+ ions you started with.

The main formula to use is concentration (mol/dm3) = number of moles (mol) / volume (dm3)

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