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Charge Balance Approximation

  1. Feb 14, 2014 #1


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    Gold Member

    1. The problem statement, all variables and given/known data

    Question: is the charge sum an approximation?
    2. Relevant equations

    E.g. consider 0.10 M [itex]Na_{2}SO_{4}[/itex] solution.

    Charge sum appears to be 0.20 from elementary stoichiometric considerations.

    3. The attempt at a solution

    The charge sum, however, seems to be ignoring the auto-ionization of water, which forms two ions - hydronium and hydroxide. Am I correct? This doesn't make a significant difference for most solution considerations, right?
  2. jcsd
  3. Feb 14, 2014 #2


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    Staff: Mentor

    We often ignore ions present in very small concentrations, but full charge balance equation for sodium sulfate solution is

    [tex][Na^+] + [H^+] = 2[SO_4^{2-}] + [OH^-][/tex]
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