Question

How does Ka relate to acid strength?

Answer 1

`K_a` is the acid dissociation constant.

The `K_a` for `CH_3COOH` is `1.8xx10^-5` (in water).

It does not determine absolute acid strength, though, only relative (to the solvent), so keep that in mind. That aside, assuming we are using water as the solvent, acetic acid thus is considered a weak acid, with `pKa = 4.76` `(-logK_a = pK_a)`.

The higher `K_a` is, the more easily the acid dissociates, and the stronger it is (i.e. the weaker the base it is, and the less strongly its bonds are held together by electron donation).