3.3A THE ACIDITY CONATANT Ka Experiments show that in a 0. IM solution of acetic acid at 25C only about 1% of the acetic acid molecules ionize by transferring their protons to water. The reaction is a equilibrium, we can describe it with an expression for the equilibrium constant H3O] [CH3CO21 Kcq=TCH3CO2田2O For dilute aqueous solutions, the concentration of water is essentially constant, so the equilibrium constant can be expressed with the acidity constant(Ka) Ka= Kea hoi=i H3O][CH3CO CH3CO2HExperiments show that in a 0.1M solution of acetic acid at 25℃ only about 1% of the acetic acid molecules ionize by transferring their protons to water. The reaction is a equilibrium, we can describe it with an expression for the equilibrium constant. For dilute aqueous solutions, the concentration of water is essentially constant, so the equilibrium constant can be expressed with the acidity constant (Ka). Keq [H2 O] = [H3 O + ] [CH3 CO2 - ] [CH3 CO2 H] Ka = Keq = [H3 O + ] [CH3 CO2 - ] [CH3 CO2 H] [H2 O] 3.3A THE ACIDITY CONATANT Ka