16TQ: Aqueous Equilibria, Part One
Name: _________________________
Text Questions from Brown, et. al.
16.6
1. What does the “a” on the acid-dissociation constant, Ka, denote?
2. The acidic behavior of weak acids is due to the ionization of the hydrogen atoms that are bonded to
__________ atoms, not the ones bonded to _________ atoms.
3. What is the relationship between the magnitude of Ka and the strength of a weak acid?
4. In many cases, the small magnitude of Ka values allows us to do what?
5. What occurs in solution such that a calculated pH for a weak acid always represents an equilibrium
condition?
6. What is the relationship between the strength of an acid and the percent ionization?
7. Write the equation for the percent ionization of an acid.
8. Take the following steps to determine the [H+] and pH of a weak acid solution.
A. Write the ___________ ______________ (i.e., the “dissociation equation”) for the weak acid.
B. Write the ____________-___________ expression, with the appropriate value for ___.
C. Make a table, with the _____________ ________________ shown on the last line.
D. _____________ the equilibrium concentrations into the equilibrium-constant expression.
E. Solve the resulting _________ equation; sometimes, we can _________ the problem by noting that
the value of Ka is _______.
9. When is it better to use the quadratic formula, rather than a simplifying assumption?
10. As the concentration of a weak acid increases, WHAT increases and WHAT decreases?
11. What are polyprotic acids?
12. Why do the Ka values for polyprotic acids become smaller as successive protons are removed?
13. Sulfuric acid is a strong acid with respect to what?
14. When is it possible to obtain a satisfactory estimate of the pH of a polyprotic acid by treating it as a
monoprotic acid?
16.7
15. Write the general form of the reaction that shows the behavior of a weak base in water.
16. Write the equilibrium-constant expression for the equation in Q15.
17. The constant Kb always refers to…
18. Why must weak bases contain one or more lone pairs of electrons?
19. Describe the first category of substances that behave as a weak base, and name the class of
compounds that is an example.
20. Describe the second category of substances that behave as a weak base, and give one example.
16.8
21. When two equations are added to give a third, the equilibrium constant for the third equation is equal to
what?
22. Write, in words, the meaning of the following equation:
Ka x Kb = Kw
23. What is the relationship between the strength of an acid and that of its conjugate base?
24. Why do many references NOT contain Kb values for anions of weak acids?
25. What is the equation that relates pKa and pKb?
16.9
26. What are the acid-base properties of salt solutions due to?
27. A. In general, what can the anion X– be considered to be?
B. If X– would react with H+ to give a strong acid, then X– will have a ___________ tendency to abstract
protons from water.
C. If X– would react with H+ to give a weak acid, then X– will react with _______ to produce the ______
______ and ____________ _____.
28. For anions that still have ___________ protons, the pH will be determined by the relative magnitudes of
Ka and Kb. If Ka > Kb, then the solution will be ________; if Kb > Ka, then the solution will be ________.
29. Most metal ions (except ________ ______ ions and the heavier _________ ______ ______ ions) can
also react with water to do what?
16.10
30. Draw how the H–X bond must be polarized if it is to transfer a proton.
31. A. Why don’t metal hydrides transfer protons?
B. Why doesn’t the C–H bond allow protons to be transferred?
32. What is the relationship between the strength of the H–X bond and acid strength?
33. What is the relationship between the stability of the conjugate base X– and acid strength?
34. Bond strength is the most important factor in determining acid strength for the binary acids in which X is
in the same _______. As X increases in size, acid strength __________ because bond strength
____________.
35. Bond polarity is the most important factor in determining acid strength for the binary acids in which X is
in the same _________. As the electronegativity of X increases, acid strength ___________ because
bond polarity ___________.
36. What are oxyacids?
37. With reference to the Y–O–H figure at the bottom of page 700…
If Y is a metal (like Na, K, or Mg), the substance readily ______ the –OH, and the substance is a
______. If Y is a nonmetal, it is bound to the O by a ________ bond; the substance does NOT readily
_____ the –OH, and it will be either _________ or ________.
38. For oxyacids that have the same number of –OH groups and the same number of O atoms, acid
strength increases with…
39. For oxyacids that have the same central atom Y, acid strength increases as…
40. A. Carboxylic acids contain the group called the…
B. This group is often written as…
C. Carboxylic acids constitute the largest category of…
41. What is the difference between a Lewis acid and a Lewis base?
42. What is the advantage of the Lewis theory?
43. A. A substance like BF3 acts as a Lewis acid because it…
B. A species like Fe3+ acts as a Lewis acid because it…
44. Why do metal ions attract the unshared electron pairs of water molecules?
45. During hydration, which species acts as the Lewis acid and which acts as the Lewis base?
46. Acid-dissociation constants for hydrolysis reactions increase with what two things?