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Reducing and Oxidizing agents

metukah

Full Member
7+ Year Member
Jun 12, 2009
162
17
  1. Medical Student
    What is the fastest way of determining what is the reducing agent and oxidizing agent in this equation:

    2HCl + H2O2 + MnO2 ---> O2 + MnCl2 + 2H2O

    Do you have to figure out the oxidation number for each reactant and then see how this changed in the products? This seems too time consuming. Is there a trick?

    Thanks!
     

    AlexB

    Full Member
    May 20, 2010
    124
    0
    1. Pre-Medical
      What is the fastest way of determining what is the reducing agent and oxidizing agent in this equation:

      2HCl + H2O2 + MnO2 ---> O2 + MnCl2 + 2H2O

      Do you have to figure out the oxidation number for each reactant and then see how this changed in the products? This seems too time consuming. Is there a trick?

      Thanks!

      Ah that makes two of us confused dods. I'm curious to hear a faster solution as well.
       

      loveoforganic

      -Account Deactivated-
      10+ Year Member
      Jan 30, 2009
      4,218
      13
        Sorry, but that's not right.

        The autodecomposition of hydrogen peroxide to water and oxygen is a redox reaction - oxygen goes from -1 in H2O2 to -2 in H2O and 0 in O2. This is a disproportionation reaction.

        HCl is not an oxidizing or reducing species here.

        H2O2 acts as a reducing agent here, and MnO2 acts as the oxidizing agent.

        In each species, oxygen is being oxidized (-1 -> 0) and manganese is being reduced (+4 -> +2).
         
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        Oct 25, 2009
        1,158
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        1. Pre-Medical
          Isn't H +2 when with peroxides?

          No.

          There is actually no such case - that I know of - in which hydrogen has +2 oxidation state. It is almost always +1 unless it is a part of metal hydride (LiH or NaH for example) that it becomes -1.

          The change in oxidation states here is with oxygen, which becomes -1 instead of -2. This is one of the few exceptions that you may have learned in your laboratory courses (hydrogen peroxide is a commonly discussed compound).

          Reference source (if interested):

          http://www.science.uwaterloo.ca/~cchieh/cact/c123/oxidstat.html
           
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