what is the relationship between ka and ph?
Note that x is Related to pH and Calculate Ka As noted above, [H3O+] = 10-pH. Since x = [H3O+] and you know the pH of the solution, you can write x = 10-2.4. It is now possible to find a numerical value for Ka. Ka = (10-2.4)2 /(0.9 - 10-2.4) = 1.8 x 10-5.