[ctpengage]

THe number of moles of water of crystallisation (x) present in hydrated ammonium iron (II) sulfate, Fe(NH4)2(SO4)2 . xH2O can be determined by oxidising the iron (II) ions with aqueous potassium permanganate in acidified solution. The ionic equation for the reaction is:
MNO4- (aq) + 5FE2+ (aq) + 8 H+(a) ---> Mn2+ (aq) + 5 Fe3+ (aq) + 4H2O (l)
It is found that when 0.980g of the compound is dissolved in 25.0cm^3 of water and titrated with 0.0300mol dm^-3 aqueous permanganate, 16.7 cm^3 are required for complete reaction.

Now I have figured out that the amount of potassium permanganate is 5.01x10^-4 moles, the amount of iron (II) ions present in the solution is 2.51x10^-3 moles and that the mass of the anhydrous solid that must have been present is 0.711g. However that's where I'm stuck. I don't know how to proceed.

Any help would be greatly appreciated. Thanks

[vhpk]

THe number of moles of water of crystallisation (x) present in hydrated ammonium iron (II) sulfate, Fe(NH4)2(SO4)2 . xH2O can be determined by oxidising the iron (II) ions with aqueous potassium permanganate in acidified solution. The ionic equation for the reaction is:
MNO4- (aq) + 5FE2+ (aq) + 8 H+(a) ---> Mn2+ (aq) + 5 Fe3+ (aq) + 4H2O (l)
It is found that when 0.980g of the compound is dissolved in 25.0cm^3 of water and titrated with 0.0300mol dm^-3 aqueous permanganate, 16.7 cm^3 are required for complete reaction.

Now I have figured out that the amount of potassium permanganate is 5.01x10^-4 moles, the amount of iron (II) ions present in the solution is 2.51x10^-3 moles and that the mass of the anhydrous solid that must have been present is 0.711g. However that's where I'm stuck. I don't know how to proceed.

Any help would be greatly appreciated. Thanks

No, that's right. What can be wrong with it? After finding the mass of anhydrous salt, you can calculate the mass of water and then is the mole number. Compare this with the one you've found of ion ferrous to find x.

[ctpengage]

thanks