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pK... Rate Topic: -----

#1 29 August 2010 - 04:47 PM krio 


Lepton
Why acids have a small pK value while bases have a higher pK value ?
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#2 29 August 2010 - 07:56 PM cypress 


Meson
I assume when you ask about pK you mean pKa. pKa is small for acids because of the definition. Ka = [H+][A-]/[AH] and pKa = -log10Ka so the greater the disassociation to H+ and A- the smaller the pKa, therefore acids have smaller pKa's than bases.

Note that bases have smaller pKb's where Kb = [HB+][OH-]/[B] and pKb = -log10Kb

This post has been edited by cypress: 29 August 2010 - 07:57 PM

Life is incredible
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#3 30 August 2010 - 12:23 PM User is online  mississippichem 


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fluorescent protein
Don't forget that K_w =[K_a ][K_b ] . So Ka and Kb must be inversely proportional.
You've come a long way. Remember back when we defined what a velocity meant? Now we are talking about an antisymmetric tensor of second rank in four dimensions.

-Feynman Lectures on Physics II
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#4 30 August 2010 - 02:45 PM John Cuthber 


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Chemistry Expert
Are you just wondering why the scale is "the wrong way up"? with strong acids getting a small number?
If so that's because they chose to get rid of the minus sign.
What's this signature thingy then? Did you know Santa only brings presents to people who click the + sign? -->
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