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!

Oxidation related question

  1. Nov 2, 2004 #1
    Hi All,

    [itex]\mathrm{Fe^{3+}(aq) + SCN^{-} (aq) \rightleftharpoons FeSCN^{2+}(aq)}[/itex]

    I add some [itex]\mathrm{NaHSO_{3}(s)}[/itex] to the above reaction !

    This makes the above chemical solution sour, consequently in a sour solution [itex]\mathrm{HSO^{-}_{3}}[/itex] will reduce Fe^{3+} to Fe^{2+}, meanwhile [itex]HSO_{3}^{-}[/itex] is itself oxidated to [itex]SO^{2-}_{4}[/itex].

    a/ The color of the original resolution changes then adding [itex]\mathrm{NaHSO_{3}(s)}[/itex] to yellow.

    b/ By adding [itex]\mathrm{NaHSO_{3}(s)}[/itex] to the orginal solution the equilibrium direction changes, such that it runs from right to left.

    c/ I need help writing the reaction between [itex]HSO^{-}_{3}[/itex] and [itex]SO^{-}_{4}[/itex].

    d/ Which influence does the adding of [itex]HSO^{-}_{3}[/itex] have on the concentration of [itex]Fe^{3+}[/itex]

    I hope that there someone out there who is willing to assist me since this is my last post !

  2. jcsd
  3. Nov 2, 2004 #2


    User Avatar
    Science Advisor
    Gold Member


    Let me first do the redox thing in atomic level, since it's easier than dealing with a bunch of atoms.

    We know that iron(III) is reduced to iron(II), and in turn, sulfite (S4+) is oxidized to sulfate (S6+):

    [tex]S^{4+} \longrightarrow S^{6+}+2e^- [/tex]
    [tex]2Fe^{3+}+2e^-\longrightarrow 2Fe^{2+} [/tex]
    [tex]S^{4+}+2Fe^{3+} \longrightarrow S^{6+}+2Fe^{2+}[/tex]

    In the real redox, you'll need to put some other correcting factors (water and hydroxide, I think) to balance additional oxygens.

    Now that we've got rid of the redox reaction, we may look other things. When you add some sodium bisulfate to the medium, a redox reaction occurs; and so the thiocyanate complex changes from [itex]\displaystyle Fe(SCN)^{2+}[/itex] to [itex]\displaystyle Fe(SCN)^+[/itex]; this gives a totally different color. Iron(II) sulfate is also formed from the reaction, and the color may have also come from this one, so I don't think that the equilibrium shifts to the left, but I may be wrong; I don't insist on that.
    Last edited: Nov 2, 2004
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Oxidation related question
  1. Oxide coating question (Replies: 4)