What does the ionization constant of an acid or a base indicate about either the acid or the base?
It tells you about the strength of the acid or base in a solution, meaning the extent of the forward reaction compared to the reverse reaction.
Let's look at the ionization of an acid, HA (all species here are aqueous):
#HA rightleftharpoons H^+ + A^-#
In aqueous solution, the acid,
Therefore, the acid ionization constant can be determined from this equation:
where the square brackets indicate the equilibrium concentration for each chemical species.
As the strength of acid increases,
- the higher the value of
#K_a#, the stronger it is as an acid in a solution.
- the lower the value of
#K_a#, the weaker it is as an acid in a solution.
Similar rationale can be applied to the ionization of a general base, B, except that the equation will look like this:
#B + H_2O(l) rightleftharpoons HB^+ + OH^-#
Therefore, the base ionization constant can be determined from this equation:
where as before, we have equilibrium concentrations for each species.