The Conjugate Seesaw

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Postby MMckinney_4H » Wed Dec 04, 2019 8:43 pm

Anybody have a thorough explanation on how to determine strength of bases? I recognize that BrO- is the conjugate base for HBrO so it would be pretty strong but how do I know definitively that it is stronger than C17H19O3N or any other base?

Justin Ko 4C
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Joined: Mon Sep 23, 2019 12:17 am

Re: 6C.17

Postby Justin Ko 4C » Wed Dec 04, 2019 9:58 pm

We know that the smaller the pKb of a base, the stronger the base. Using chart 6C.2 from the textbook, we find that pKb of morphine is 5.79. In order to find the pkb of BrO-, we need to take the pKw (which is the equilibrium of pure water) and subtract the pKa of the conjugate acid of BrO- (which is the hypobromous acid, HBrO). By using chart 6C.1 in the textbook, we find that the pKa of HBrO is 8.69. So, pKb(BrO-) = pKw - pKa = 14 - 8.69 = 5.31. Since pKb(Morphine) > pKb(BrO-), the hypobromite ion is a stronger base.

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