From pK a to the pH of weak base solutions.

Undergraduate biochemistry students frequently find the quantitative treatment of weak acids and bases troublesome. Given the pK(a) of a weak acid HA, for instance, many students struggle to calculate the pH of a solution of the conjugate base A(-) at concentration C, pH(A(-), C). The traditional method involves calculating the base dissociation constant K-b and the artificial quantity pOH before reaching pH, but these steps increase the risk of mistakes and provide little insight into acid-base equilibria. The alternative method presented here allows students to calculate the pH of a weak base solution from the pK(a) of its conjugate acid without calculating K-b and pOH, using a memorable relationship: pH(HA, C) + pH(A(-), C) = pK(a) + 7.