soma
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trying to understand Ka
I'm wondering what the Ka of a substance is at 50% dissociation. If Ka=[A-][H+]/AH then e.g. if you have 6 moles of acetic acid and it's 50%
dissociated, then you would have 3 moles of H+ and 3 moles of CH3CO2. Would that mean Ka=3x3/6?
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Metacelsus
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No. First, you need to express [HA], [A-], and [H+] as concentrations, not amounts of moles. This is because there's an implicit
solvent term in the equilibrium constant.
Assuming 1 liter of an ideal solution, Ka would be (3*3)/3 = 3. This is because there are only 3 moles/liter of HA left after 3 moles/liter
have dissociated.
The actual Ka of acetic acid is 1.75*10−5
[Edited on 4-16-2016 by Metacelsus]
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