[globusine]

Given:
A product contains magnetite (Fe3O4 = Fe2O3.FeO), ferric oxide and nonreducible oxides by permanganate. A sample of 0.600 g is dissolved after fusion and the iron in solution is reduced in acid environment. After elimination of the excess of reducer, a potentiometric titration of Fe(II) by KMnO4 0.02 mol/l needs 42 ml of this solution. In addition a sample of 1.000 g is dissolved in H2SO4 + HF in inert atmosphere to avoid any oxidation of Fe(II). The solution is simply diluted and the titration of Fe(II) consumes 20 ml of the KMnO4 solution.

Question to be answerd
) Calculate the percentages in weight of magnetite and ferric oxide in the sample

The answer I think is alright? Please can you check and tell me if I am going in the right direction?

1) calculate # moles MnO4-

 # moles MnO4-= C(MnO4-)*V(MnO4-)=0.02 mol/l*20.10^(-3)l =4.10^(-4) moles


2) calculate # moles Fe 2+ in the sample

the titration reaction (balanced) is:
8H+ + MnO4- + 5Fe 2+ -->Mn2+ + 5Fe3+ + 4H2O

#moles Fe 2+ =5* #moles MnO4-=5*4.10^(-4) moles=20.10^(-4) moles

I then assumes that # moles Fe 2+ = # moles Fe3+ ( because of the stoimetry od the titration reaction)
3) calculate the massea ( see picture attached titled masses)


mass of the sample is 1.6 g ( is this correct?)
4) I then calculate the weight percent ( see also picture attached titled weight)