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Homework Help: Balance Half-Cell Equation

  1. Jul 5, 2006 #1
    Ok, here is another one I have, this is one of a series of half-cell questions... this one is confusing.

    79. Balance the following equations by the half-cell method. Show both half-cell reactions and identify them as oxidation or reduction.
    b) Cl2(g) + OH- <=> Cl- + ClO3^- + H2O(l)

    Oxidation Reaction:
    Cl2 (g) <-> Cl-
    2e- + Cl2 <-> 2Cl- --- Balanced Cl molecules and electrons

    Reduction Reaction:
    Cl2 (g) <-> ClO3-
    Cl2 + 6H2O <-> 2ClO3- + 12H+ 10e-

    Multiply the oxidation reaction by a factor of 5 to cross out the e-
    5Cl2 <-> 10Cl-

    Add them together:
    6Cl2 + 6H2O <-> 10Cl- + 2ClO3- + 12H+

    Since this is a basic solution we must swap out the H+ with OH-... in this case adding 6OH- to each side

    6Cl2 + 6H2O + 12OH- <-> 10Cl- + 2ClO3- + 12HOH

    This seems kinda insane but it may just be right.
    Can anyone give me some input on this?
  2. jcsd
  3. Jul 5, 2006 #2
    Ha, I was just reviewing these today.
    You can cancel out the H2O since you have it on both sides.

    6Cl2 + 12OH- --> 10Cl- + 2ClO3- + 6H2O

    You can divide all of the coefficients by 2. It seems that sometimes when you work with diatomic molecules like Cl2 that your final answer will be doubled. I made the same mistake here: https://www.physicsforums.com/showthread.php?t=96870

    3Cl2 + 6OH- --> 5Cl- + ClO3- + 3H2O

    Copy and paste that line into google and the results show that you're good :smile: .
    Last edited: Jul 5, 2006
  4. Jul 5, 2006 #3


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    This thread is a double-post. The other copy is in Chemistry.

    Yellowduck - please do not post multiple copies of the same thing!
  5. Jul 6, 2006 #4


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