The al 3 ion is capable of supporting the ionization

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Fundamentals of Analytical Chemistry
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Chapter 14 / Exercise 14-7
Fundamentals of Analytical Chemistry
Skoog/West
Expert Verified
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.
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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 Mcheck 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
a
(TRUE)
answer (c)
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Fundamentals of Analytical Chemistry
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Chapter 14 / Exercise 14-7
Fundamentals of Analytical Chemistry
Skoog/West
Expert Verified
11. The “brute force” method is to find the pKa’s for the acids and see which one is closest to 7.30pKa = −log (Ka) (a) for 2-ethanolaminium, pK = − log (3.18x10−10) = The others are found in the same way and are(b) pKa = 9.36(c) 6.95(d) 8.04 choose the one closest to the target pH, which is (c) correct. (answer (d) was also accepted for partial credit bec. it is within +1 pH unit of the target pH.12. See page 670-673 in your textbook for a complete explanation. 4 of the 6 pairings in this question contained one acid from your strong acid short list, and one other acid. These should have been very easy to predict. The strong acid is stronger!H2SO3stronger than H2S bec. more electron withdrawing groups (the O’s) and the H+ has less electron density around it than in the covalent bond in H2S.HI >> HF because the bond strength HF much greater. F is smaller radius. HI on short list.HNO3>> HNO2more electron withdrawing groups on HNO3HNO3on short listHCl >> HCNHCl is on short listH2SO4> H3PO4H2SO4on short listH3PO4> H3AsO4
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