In solving weak acid equilibrium problems to find [H+] or pH, a major assumption is usually made. This major assumption can be represented by the following:
1.8 x 10-5 = x2 / (0.10 - x) = ca. x2 / 0.10
Which of the statements below can be cited as proof that the assumption is reasonable?
simplifications can be made when [HA]initial is exactly equal to 100Ka
the assumption works if x is within 5% of [HA] initial
for the assumption to be used, the pH of the solution cannot be less than 5.0
x is small so [HA]equilibrium<< [HA] initial