Percent Ionization of weak acids The more dilute the solution of a weak acid, the greater the degree of ionization (percent ionization). Think about it, good old Le Chatelier’s principle say adding more water to an equilibrium system would cause a shift to the right making more of the ionized acid species. Percent ionization (p) = concentration of acid ionized x 100% Concentration of acid solute For a general weak acid: HA(aq) H+(aq) + A-(aq) [H+] = p x [HA] 100% Example: The pH of 0.10 M formic acid is found to be 2.38. What is the percent ionization for this acid? Make sure you practice questions dealing with percent ionization and equilibrium calculations. Refer to page 397 in your textbook.