Kb

Smooth Operater

don't bug "operatEr"!
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5+ Year Member
May 22, 2004
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    the equation for dissociation of weak base in water is:

    B- + H2O --> HB + OH-

    but how come kaplan shows that the Kb for weak base is:
    Kb = [B+][OH-]/[BH]

    should it be Kb = [HB][OH-]/[B-] according to the above equation?

    Am I making mistake somewhere? Thanks! :thumbup:
     

    sgdorfl90

    Senior Member
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    May 12, 2005
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      Smooth Operater said:

      you are right and so is Kaplan. When talking acids and bases, it is important to remember amino acids and such are poylprotic, meaning they can release multiple H and gain the same amount. The equation you used can be like an amino acid glycine, in NH2 and COO- form, this would make ur molecule have a - charge and it will be a very effective base since NH2 is a moderately strong base. Kaplan altered this molecule to have a protonated amine, NH3+ and COO- group. In this case, the molecule is zwitterion and is neutral, hence the B alone. Now, if you react B + H20, it will slap a hydrogen on the B, to make it B+. Hope that helps.
       
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