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Posted by on Saturday, March 30, 2013 at 11:17pm.

What are some of the equilibrium expressions that chemists use for weak acid equilibrium?

  • Chemistry - , Saturday, March 30, 2013 at 11:21pm

    Ka = (products)/(reactants)
    with coefficients becoming exponents.

  • Chemistry - , Saturday, March 30, 2013 at 11:27pm

    Are there any more expressions for weak acids equilibrium? It would be helpful in the long run to know what they all are if there are any more.

  • Chemistry - , Sunday, March 31, 2013 at 12:14am

    You're question is so general that I didn't know what to write the first time and certainly I don't know what to write now. For a weak acid, such as HA, it ionizes as
    HA(aq) + H2O(l) ==> H3O^+(aq) + A^-(aq) in which aq stands for aqueous (as in solution) and l stands for liquid (meaning pure H2O), the
    Ka = (H3O^+)(A^-)/(HA)
    All follow that same generic Ka. There are some diprotic and triprotic acids but they follow the same rules. For example, H2CO3 is
    H2CO3(aq) + H2O(l) ==>H3O^+(aq) + HCO3^-(aq) and k1 for that ionization is
    k1 = (H3O^+)(HCO3^-)/(H2CO3)

    The second hydrogen then ionizes as
    HCO3^-(aq) + H2O(l) ==>H3O^+(aq) + CO3^2-(aq) for which k2 is
    k2 = (H3O^+)(CO3^2-)/(HCO3^-)
    etc.

    H3PO4, a triprotic acid, works the same way and it has a k1, a k2, and a k3 in which one H comes off at a time.
    If you have a specific problem it would be easier to answer that than trying to stay with general cases.

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