Question

Determine the Relative strength of weak acids and bases.

Answer 1

The relative strength of weak acids and bases are generally determined by their dissociation constants K_a and K_b respectively. For weak acid, i.e. CH₃COOH

K_a and K_b are just the equilibrium constants and hence depends only on temperature. Greater the value of dissociation constant of the acid (K_a), more is the strength of the acid and similarly greater the value of dissociation constant of the base, more is the strength of the base. For two acids of equimolar concentrations.

The modern method is to convert K_a as a power of 10 and express acid strength by power of 10 with sign changed and call this new unit pK_a. Thus, if K_a for acid is equal to 10^–4, pK_a = 4. So higher pK_a value means lower acid strength, 

that is, pK_a = – log K_a 

Also, pK_b = – log K_b