9. The Al3+ion is capable of supporting the ionization of its sphere of hydration and will act as a weak acid in water. This fact is supported by the Kawhich was given in the problem. The acetate ion should be recognized as the conjugate weak base of acetic acid, whose Kawas also given. Find Kbfor acetate ion and compare how strong acetate is as a base, with how strong Al3+ is as an acid.
10. Recognize the phenolate ion as a weak base. Recognize the Na+ ion as functionally neutral in water.Solve for the pH of a weak base solution: Kbis found from the Kagiven for its conjugate acid and is Kb= Kw / KbbKCOH≈-][= 1014101.11000.1)250.0(--xx= 0.00472 M♦ check to see if [OH−]approx is greater than 10 % of Cb. ? 0.00472 < (0.250)(0.1) ♦ assumption that amount ionized is “negligible” compared to Cb is valid. No quadratic needed.pOH = −log (0.00472 M) = 2.32 andpH = 14 − pOH = 11.68