Equation is HA → H+ + A- KA = [H+][A-]/[HA]
Let's say that x = HA that ionizes in molarity
.00361 = x2/(.155-x) This can be solved for x as a quadratic equation or you can assume that x<<.155
(Usually you want KA to be about 10-5 to get away with that - it doesn't work here)
After solving the equation for x %ionization = (x/.155)*100