Smooth Operater

don't bug "operatEr"!
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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

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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.