Carboxylic acids are weak acids and dissociate in aqueous solution to the carboxylate anion. The extent of dissociation is given by the equilibrium dissociation constant, K a, which is often expressed in its logarithmic form as pK a. (The cation is written simply as H+ and is understood to be solvated with one or more water molecules in solution.)If a butyric acid/butyrate buffer is 0.033 M in butyric acid and has a pH of 4.77, what is the molar concentration of the butyrate ion? The pK a of butyric acid is 4.81.