# What are some examples of the properties of bases?

Oct 20, 2015
• They might want protons (Bronsted-Lowry definition)
• They might want to donate electrons (Lewis definition)
• They might donate ${\text{OH}}^{-}$ to solution (Arrhenius definition)
• The conjugate base of a weak acid is a strong base
• The conjugate base of a strong acid is a weak base

A nice example of something that has most of the following properties is ${\text{HSO}}_{4}^{-}$. This base wants a proton according to the Bronsted-Lowry definition, and it will get that proton by donating electrons according to the Lewis definition, using the lone pairs on the ${\text{O}}^{-}$.

It is the conjugate base of ${\text{H"_2"SO}}_{4}$, a strong acid; thus, it is a weak base.

(Since the $\text{pKa}$ of ${\text{H"_2"SO}}_{4}$ is about $1000$, it is reasonable to say that most ${\text{H"_2"SO}}_{4}$ is actually deprotonated.)

Furthermore, although it might be difficult, it can be deprotonated to get ${\text{SO}}_{4}^{2 -}$ (the $\text{pKa}$ of ${\text{HSO}}_{4}^{-}$ is about $2$). That makes it also a (relatively strong weak) acid by the Bronsted-Lowry definition, because it can donate a proton, AND it makes it a (relatively strong weak) acid by the Lewis definition, because it accepts electrons in order to donate that proton.

(This makes the conjugate base, ${\text{SO}}_{4}^{2 -}$, a strong base.)

It is not, however, a base by the Arrhenius definition, but an acid. It donates protons (${\text{H}}^{+}$) to solution upon dissociation, while donating ${\text{OH}}^{-}$ would require disrupting its resonance structures, which is unfavorable.