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Homework Help: Chemistry Exam: Least do I know!

  1. Sep 22, 2007 #1
    Well, well, well, I am currently going to have Chemistry exams in a few days. I have something of a lot portion to study. I really get confused with the determination of Oxidation No. despite the methods shown in textbook! I have a chapter relating to basics of Structure of an Atom. Now in this I get confused with the various relations and equations. Is that Balmer's series, de Broglie's theory, everything that important for the current chemistry?

    Somebody, at the moment, please give me some tips to Oxidation Number determination. Even the thing of balancing the redox reactions confuses me to some extent. There are two methods in the textbook we have: Ion-electron method and Half-reaction method. Some some, more easier method?
  2. jcsd
  3. Sep 22, 2007 #2


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    ONE atom in an ion will change in its 'electronic state' (may need better terminology), but all the other atoms which may be part of this ion will have each of their predictable electronic states.. like Oxygen will almost always be -2. You find the electronic state by accounting for the electronic states of each atom in the ion; the sum of these values must give the charge of the ion.

    Example Permanganate: MnO4 (-1)
    if u=uknown charge on Mn, then
    -1 = 4*(-2) + u
    Find value of u.

    If permanganate reacts, then it will probably be the oxidizing agent and something else must be the reducing agent. the Mn will undergo a half reaction and go into a reduced form; the Mn will need to gain some electrons while the other reactant will need to donate electrons.
  4. Sep 22, 2007 #3
    But isn't it like Oxygen has various other oxidation state too? Its always easy to find an oxidation number with oxygen or hydrogen in it, right? But how do we come to know what Oxygen will have from -1,-2, or +1, +2? Hydrogen too accounts for -1 and +1 ... when Hydrogen reacts with a metal, it probably is a negative oxidation state, but how do you determine whether that number for oxygen is 2 or 1?
  5. Sep 23, 2007 #4
    There are the oxidation rules and it depends on the textbook that you use. They go in order and if hydrogen is around, hydrogen is labelled first as +1. Then you determine oxygen's oxid #. Ex. If you have H2O, you label H as +1 and then find out O as -2 by the method symbolipoint said: H2O = 0 (because its a neutral molecule)
    2H + O = 0
    2(1) + O = 0
    O = -2
    Ex H2O2 (hydrogen peroxide)
    2H + 2O = 0
    2(1) + 2O = 0
    O = -1
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