1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Finding composition of mixture of Fe3O4 and Fe2O3

  1. Jan 5, 2016 #1

    Titan97

    User Avatar
    Gold Member

    1. The problem statement, all variables and given/known data
    An ##\mathrm{8~g}## sample of ##{Fe_3O_4}## and ##{Fe_2O_3}## containing some inert impurity was treated with excess of ##\mathrm{aq}## ##{KI}## in acidic medium. which converted all iron to ##Fe^{2+}##. The resulting solution was then diluted to ##\mathrm{50~ml}##.

    ##\mathrm{10~ml}## of it was taken and the liberated iodine required ##\mathrm{7.2~ml}## of ##\mathrm{1M}## sodium thiosulphate to reduce all iodine.

    Another ##\mathrm{25~ml}## was taken and the iodine was removed. The remaining solution required ##\mathrm{4.2~mL}## of ##\mathrm{1M}## ##{KMnO_4}## to oxidize all ##Fe^{2+}##.

    Calculate the percentage of composition of the mixture.
    The initial solution already contains ##Fe^{2+}## from ##FeO## whic does not react until the second titration.


    2. Relevant equations
    equivalence concept

    3. The attempt at a solution

    Working backwards, milli equivalence of ##{Fe^{2+}}## is ##\mathrm{5\times 4.2\times 1=21}## in ##\mathrm{25~mL}## solution. So in ##\mathrm{50~mL}##, the amount of ##{Fe^2+}## is ##\mathrm{42}## m.eq.

    Similarly, the m.eq of iodine from titration with thiosulphate is ##\mathrm{36}##

    From the first reaction (with iodide), $$\mathrm{m.eq~of~iodine~liberated=m.eq~of~Fe^{2+}~formed}$$
    The excess ##{Fe^{2+}}## is from ##{FeO}## which is present in ##{Fe_3O_4}##

    amount of ##{FeO}## is ##\mathrm{6~m.eq}##.
    Hence its weight is ##\frac{6}{1000}\times\frac{72}{2}=\mathrm{0.216~g}## since n-factor is ##\mathrm{2}##.

    Since ##\mathrm{1~mol}## of ##{Fe_3O_4}## conatains ##\mathrm{72~g}## of ##{FeO}##, the amount of ##{Fe_3O_4}## is ##\mathrm{0.6945~g}##. But this answer is wrong. Is there anything wrong in my procedure?
     
  2. jcsd
  3. Jan 5, 2016 #2

    Borek

    User Avatar

    Staff: Mentor

    I haven't checked other things, as this caught my attention first:

    Are you sure you are not tricking yourself with equivalents?
     
  4. Jan 5, 2016 #3

    Titan97

    User Avatar
    Gold Member

    During the calculation, I got different values for iodine and fe2+. This is because a part of the fe2+ is from FeO which was already present. When KI is added, the meq of iodine formed will be equal to the meq of Fe3+ formed=meq of Fe2+ reacted.
     
  5. Jan 5, 2016 #4

    Borek

    User Avatar

    Staff: Mentor

    I strongly suggest you redo the calculations using moles.
     
  6. Jan 5, 2016 #5

    Titan97

    User Avatar
    Gold Member

    OK. But before that, can you help with the reaction of Fe3Or? Should I take fe3o4 as one mole of FeO and one mole of Fe2O3.
     
  7. Jan 6, 2016 #6

    Borek

    User Avatar

    Staff: Mentor

    Yes, it is a mixed oxide.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Finding composition of mixture of Fe3O4 and Fe2O3
Loading...