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Homework Help: Tough electrolysis question (really )

  1. Mar 31, 2008 #1
    tough electrolysis question (really!!!)

    1. The problem statement, all variables and given/known data

    When an iron sheet is made the anode during electrolysis of very conc. KOH, an anion containing iron in a high oxidation state is formed in solution. The addition of an excess of Ba(NO3)2 to this solution precipitates a red solid having the following composition by mass:

    Ba: 53.3%
    Fe: 21.7%
    O: 24.9%

    (1) Calculate the empirical formula of the red solid an dthe oxidation number of the iron in it.

    (2) After a current has been passed through the solution for some time, the addition of Ba(NO3)2 produces 1.00 g of the red solid. Calculate how many moles of the red solid are formed, and hence calculate how many coulombs of electricity were needed.

    2. Relevant equations

    3. The attempt at a solution

    the first part is ok, i got FeO4 as empirical formula. i got the charge on the anion to be -2 since i assumed that it is associated with Ba2+. then the OS of iron becomes +6.

    for the second part i dunno if i have to take the actual anion to be (FeO4)2- and find the Mr, then the number of moles. because what i have is only the empirical formula.

    it would be nice if someone could tell me how is that anion actually formed.
  2. jcsd
  3. Mar 31, 2008 #2


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    What did you get for the red solid? It is 53% by weight barium..... Assume that barium is always +2 and that oxygen is -2.
  4. Mar 31, 2008 #3
    would it be correct if i do 53% of the Mr is 137, therefore 100% will give the Mr of the solid?

    yeah, it's ok. but now, i wanted to know how this anion is formed.
  5. Apr 1, 2008 #4


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    If it is indeed the correct answer, it is called ferrate. It is beleived to be isostructural with chromate ([tex]CrO_4^{-2}[/tex]) and permanganate ([tex]MnO_4^-[/tex]). It is fairly unstabe but recent advances have been made to isolate it as the potassium salt from the treatment of ferric chloride, KOH and hypochlorite. That solid is now sold by Ferratec and is used in water treatment as a combination selective oxidant (for sulfides) and flocculant (soluble iron). I don't know the mechanism.
  6. Apr 1, 2008 #5
    cool.... thnks
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