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Determining acid/base properties

  1. Sep 13, 2014 #1
    How can you tell NH3 is a better base than HOCOO-?

    I look at the conjugate species in both to determine their relative stabilities. Where NH4+ is the conjugate acid of ammonia and HOCOOH the conjugate acid for acetate. In this case, isn't the NH3 more stable than NH4+ since it is uncharged yet still has a full octet on the N? Also, wouldn't the HOCOOH be more stable than HOCOO- since it's not charged and thus doesn't even have any charge to spread. Therefore, using this reasoning of the actual charges, should HOCOO- be the better base since its conjugate acid is more stable (lower in energy; it is weaker than NH4+)?

    I'm sure there are other properties like the electronegativity of the atom bearing the charge, atomic size, electron withdrawing atoms in the compounds and net charge, but how do you determine the priority when comparing compounds like this? Are there any other properties I'm missing?
     
  2. jcsd
  3. Sep 13, 2014 #2

    epenguin

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    HOCOOH is carbonic acid not acetic so you need to clarify what you are talking about.
     
  4. Sep 14, 2014 #3

    Borek

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    The only sure way is to test it experimentally.
     
  5. Sep 14, 2014 #4
    Okay. Is there a framework for analyzing properties of the molecules to at least make an educated guess before experiment? I tried to look at electronegativity, atomic size, resonance and inductive effect but may be looking past something.

    I try to rationalize that -COOH is more stable than NH4+ since it is uncharged and has full octets while the other has a charge, but this doesn't coincide with experimental results. I just don't quite seem to comprehend exactly why resonance would be more stable in this case, since -COO- has a charge and I realize resonance is more stable than a localized charged, but isn't no charge for -COOH even more stable? I'm sure the solvent (water in this case) has a major role and possibly induces a strong electrostatic attraction with the partial negative oxygens, but even still, those waters are not directly bonded and thus have more unstable bonding with the negative oxygens than a strongly covalently bonded hydrogen.
     
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