Determining acid/base properties

[MathewsMD]

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?

 

[epenguin]

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?

HOCOOH is carbonic acid not acetic so you need to clarify what you are talking about.

 

[Borek]

How can you tell NH3 is a better base than HOCOO-?

The only sure way is to test it experimentally.

 

[MathewsMD]

The only sure way is to test it experimentally.

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.

 

[LudusRex]

I would first look at the chemical structures of NH3 and HOCOO- to determine their acid/base properties. NH3 is a neutral molecule, while HOCOO- has a negative charge. In general, bases are molecules that can accept protons (H+), while acids are molecules that can donate protons.

In the case of NH3, it has a lone pair of electrons on the nitrogen atom, which makes it a good candidate for accepting protons. This is because the lone pair can easily form a bond with a proton, making NH3 a strong base.

On the other hand, HOCOO- has a negative charge on the oxygen atom, which means it is already carrying an extra electron. This makes it less likely to accept another electron, making it a weaker base compared to NH3.

Another way to determine the relative strength of a base is to look at the stability of its conjugate acid. In this case, NH4+ is the conjugate acid of NH3, while HOCOOH is the conjugate acid of HOCOO-. The stability of the conjugate acid is related to the strength of the base. A more stable conjugate acid indicates a weaker base, and vice versa. In this case, NH4+ is more stable than HOCOOH, indicating that NH3 is a stronger base than HOCOO-.

Other factors that can influence the strength of a base include electronegativity, atomic size, and electron withdrawing atoms in the compound. However, in this particular comparison, the main factor is the presence of a negative charge on HOCOO- which makes it a weaker base compared to NH3.

Overall, there are multiple properties that can be considered when determining the acid/base properties of a molecule. However, in this case, the presence of a negative charge and the stability of the conjugate acid are the main factors indicating that NH3 is a better base than HOCOO-.