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Acid/base question

Discussion in 'MCAT Study Question Q&A' started by Revilla, Dec 14, 2008.

  1. Revilla

    Revilla New Member
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    I can memorize the pattern, but I'm trying to understand it and I can't seem to wrap my head around it. Here goes:

    Which acid yields the greatest conjugate base concentration?

    The answer is the strongest acid. But here's my problem. A large base concentration would correlate to a strong base. A strong conjugate base correlates to a weak acid, so why is the answer a strong acid? A strong acid has a weak conjugate base so wouldn't the conjugate base of a strong acid have a lower concentration?
     
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  3. G1SG2

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    The question is asking which acid yields the greatest conjugate base concentration, not which yields the greatest concentration of the strongest base. A strong acid dissociates completely, and would yield the greatest conjugate base concentration.

    Not necessarily. A large base concentration could be a concentration of a weak base, which can be resultant of the complete dissociation of a strong acid.

    For example, take HCl vs CH3COOH

    HCl--> H+ + Cl-

    CH3COOH --> H+ + CH3COO-

    In the first example, you would have more concentration of Cl-, since HCl dissociation would go to completion since it is a stronger acid. In the second example, you would have less concentration of the conjugate base CH3COO- than Cl- because CH3COOH is a weaker acid.
     
    #2 G1SG2, Dec 14, 2008
    Last edited: Dec 14, 2008
  4. Ibn Rushd

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    I want to say that concentration and strength are independent of each other, but I'm not exactly sure. Hopefully someone else can chime in.

    But I think that the question wants you to understand that strong acids dissociate completely, and because they do, they generate the largest concentration of conjugate bases, relatively speaking. For example, take the strong acid HBr:

    HBr + H2O --> H3O+ + Br-

    This reaction goes to completion, so the concentration of Br-, the conjugate base, will be relatively higher compared to the concentration of the conjugate base of HF, F- (a weak acid):

    HF + H2O --> H3O+ + F-
     
  5. Revilla

    Revilla New Member
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    Okay, that makes more sense. I guess I really need to concentrate on the question and not make assumptions or leaps. Thanks, guys!

    Also, I meant to post this on the Q&A forum, if one of the moderators want to move it to avoid cluttering up the main board.
     
  6. JJMrK

    JJMrK J to the J
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    Like others have said, a strong acid will disassociate the most and leave lots of conjugate base just chillin'. It will be a weak conjugate base, because as was mentioned, a strong acid has a weak conjugate base by definition.

    Just remember, if you had a strong base, it would suck up all the H+'s and make an acid.
     
  7. Vihsadas

    Vihsadas No summer
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    Moving to Study Question Forum
     

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