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Basic concept doubts in redox reactions

  1. Jul 8, 2015 #1
    1. The problem statement, all variables and given/known data
    [C2O4]-2 ------> CO2
    Find if the reaction is oxidation or reduction and determine the no. of electrons lost or gained by carbon.

    2. Relevant equations

    3. The attempt at a solution
    I started with finding the oxidation states of both elements. It's 3+ and 2- for carbon and oxygen on the LHS and 4+ and 2- for carbon and oxygen on the RHS. But i am having trouble in interpreting these values.
    the OS of carbon goes from 3+ to 4+. My interpretation of this was that C had lost 3 electrons on the LHS while lost 4 electrons on the RHS to O. Hence I thought that C should have gained 1 electron. And this means it's reduction and that's the wrong answer. Can someone please correct my interpretation and help me out with this? This is quite a silly and basic question. Please bear with me, I am new to this.
  2. jcsd
  3. Jul 8, 2015 #2


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    Staff: Mentor

    Think it over.

    But in general, this is much easier done without oxidation numbers, just using half reactions. It is trivial to balance atoms, then it is trivial to see where the electrons have to be added (on which side) to balance the charge.
  4. Jul 8, 2015 #3
    Ok I tried again. The OS of C on LHS is 3+ meaning there are 3 more protons than electrons. This goes to a 4+ on the RHS , 4 more protons than electrons , which means 1 electron must have been removed. And balancing the reaction we get 2CO2 on the LHS. So multiplying the OS with the no of atoms., i got 6+ on the LHS and 8+ on the RHS. Hence applying the same logic, 2 electrons must have been removed? Is this right?
  5. Jul 9, 2015 #4


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    Staff: Mentor

    Yes, electrons are removed.

    C2O42- → 2CO2 + 2e-
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