What are some examples of the properties of bases?

1 Answer
Oct 20, 2015
  • They might want protons (Bronsted-Lowry definition)
  • They might want to donate electrons (Lewis definition)
  • They might donate "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 "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 "O"^(-).

It is the conjugate base of "H"_2"SO"_4, a strong acid; thus, it is a weak base.

(Since the "pKa" of "H"_2"SO"_4 is about 1000, it is reasonable to say that most "H"_2"SO"_4 is actually deprotonated.)

Furthermore, although it might be difficult, it can be deprotonated to get "SO"_4^(2-) (the "pKa" of "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, "SO"_4^(2-), a strong base.)

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