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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: bmu123 on April 25, 2015, 01:01:14 PM

Title: Working out composition of SeFe0x
Post by: bmu123 on April 25, 2015, 01:01:14 PM
A sample of the perovskite SrFeOx (A) was synthesised by heating SrCO3 and Fe2O3 in oxygen gas at 900°C.  X-ray powder diffraction data revealed a primitive unit cell for A consistent with the perovskite structure.  A small sample of A was dissolved in dilute HCl containing excess KI, and the iodine produced (corresponding to reduction of Fe(IV) to Fe(III)) was titrated with sodium thiosulphate.  The titration indicated that 72% of the iron was present as Fe(IV)

I'm confused about how to work out the composition of A from this, I know 72% of the iron is Fe3+ so 28% must be Fe3+, this makes the average Fe oxidation state 3.72+, where do I go from here? Would it be SrFeO2.86 because the overall positive charge is now +5.72 so /2 for number of oxygens needed to balance it out?

X-ray diffraction revealed that A has a primitive unit cell with length 3.898 Å.  Explain the difference between the unit cell size of A and that of SrFeO3, which has a = 3.852 Å.

I assume this has something to do with the charges but I'm not sure what.
Title: Re: Working out composition of SeFe0x
Post by: unsu on April 25, 2015, 02:35:17 PM
72%, is it a mass % or mole %?



Title: Re: Working out composition of SeFe0x
Post by: bmu123 on April 27, 2015, 01:09:52 PM
Quote from: unsu on April 25, 2015, 02:35:17 PM
72%, is it a mass % or mole %?




hmm that's the full question it doesn't say which