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Thread: Acids and bases

  1. #1 Acids and bases 
    Forum Masters Degree thyristor's Avatar
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    Hi!
    I am a little bit confused over the following. Is it possible for an acid, denoted as HA, to be less acid than its corresponding base is basic?
    To clarify, we have the following reactions:

    whereby

    and


    whereby .

    So, is it possible for K_b>K_a while HA is still an acid?


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  3. #2  
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    Yes, it can still be an acid if the kA of HA is smaller than the kB of A-. It would simply be a weak acid.


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    Forum Masters Degree thyristor's Avatar
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    Thanks! Do you know of any acid with this property? I have checked for a few, e.g. acetic acid and HSO4^-, but none of them had a K_b higher than K_a.
    Then I'm not referring to the K_a and K_b of the acid. I'm referring to the K_a of the acid, but the K_b of the corresponding base.
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  5. #4  
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    Quote Originally Posted by thyristor
    Thanks! Do you know of any acid with this property? I have checked for a few, e.g. acetic acid and HSO4^-, but none of them had a K_b higher than K_a.
    Then I'm not referring to the K_a and K_b of the acid. I'm referring to the K_a of the acid, but the K_b of the corresponding base.
    Just look at any of the weaker acids. Carbonic acid, for example. It has a Ka of 2.5*10^-4, while its conjugate base (bicarbonate) has a Kb of 5.6*10^-1. So the Kb of carbonic acid's conjugate base is about 2000 times larger than the Ka of carbonic acid, but it's still an acid.
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  6. #5  
    Forum Masters Degree thyristor's Avatar
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    Okay, thanks! I'll have to think it over. It just seemed a bit counter intuitive to me.
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