Answer key for Ch 14 Zumdahls
1. @ different temps, H2O has different values for Kw (see problem #47) – Different
Kw values will give different [H+], which will in effect change the pH, the higher the
temp the lower the pH value drops. ****Keep in mind though that the sample of
pure water will still be neutral, the [H+]=[OH-].
2. Strength refers to the ability of an acid or base to dissociate. Strong acids/bases
completely dissociate, while weak acids/bases dissociate less than 5%.
Concentration refers to the number of moles per unit of volume. Both strong and
weak acids/bases can be concentrated or dilute. HCl is strong because it completely
dissociates, it has nothing to do with its concentration. NH3 is weak because it only
dissociates a little bit when reacted with water.
4. The major species would be H+, Cl-, H2O, HA, and A-. The strong acid is 100%
dissociated, while the weak acid is less than 5% dissociated. The pH would be
determined from the strong acid.
7. There is both H+ and OH- present in the solution, using the Kw=[H+][OH-], the
amount of H+ can be calculated.
13. pH means to take the –log. True, strong acids completely dissociate which will
in general provide more H+.
14. b/c the Kw = 1 .0 x 10-14, so [H+]=[OH-]= 1.0 x 10 -7
15. Yes for example find the pH of 15M HCl.
20. a. acidic
b. acidic
c. basic
d. acidic
21. a. acidic
b. basic
c. basic
d. basic
22. [H+] is the acid component and [OH-] is the base component.
29. a. Kw=[H+][OH-]
b. Ka = [H3O+][A-]
[HA]
c. Kb = [NH4+][OH-]
[NH3]
34. Scrubbers prevent the S that is released from burning coal to mix with O2 to
form SO2 and SO3. These two gases then mix with water to produce sulfurous and
sulfuric acids which are damaging to the environment.
CaO mixes with water in the soil to produce calcium hydroxide, which raises the pH
of the soil and promotes growth of plants.
36. a Ka = [H+][CN-]
[HCN]
b. Ka=[H+][OC6H5]
[HOC6H5]
c. Ka=[H+][C6H5NH2]
[C6H5NH3+]
38. in order of the equation
a. acid + base  conj acid + conj base
b. base + acid  conj base + conj acid
c. acid + base  conj base + conj acid
40
a. right, weak
b. left, strong
c. left, strong
d. right, weak
e. right, weak
41. HClO4, HClO2, NH4+, H2O
42. NH3, ClO2-, H2O, ClO443. a. HCl
b. HNO2
c. HCN
44. a. H2O
b. NO2-
c. OC6H5-
45. a [OH-] = 1.0 x 10-7M, neutral
b. [OH-] = 12.05 M, basic
46. a. [H+] = 6.7 x 10-15M, basic
b. [H+]=2.8, acidic
47. T goes up, Kw goes up, more product is formed meaning heat must be on
reactant side, which is endothermic
b. [H+]=[OH-]= 2.34 x 10-7M
48.
a. [H+]=[OH-]=1.71 x 10-7M
b. pH = 6.77
c. pH = 12.54
52.
Solution A pOH = 4.37, [H+]= 2.3 x 10-10M, [OH-]=4.3 x 10-5M, basic
Solution B pOH = 5.40, pH=8.60, [H+]=2.5 x 10-9M, basic
Solution C pOH= 12.43, pH=1.57, [OH-]= 3.7 x 10-13 M, acidic
Solution D pH=12.78, [H+]=1.7 x 10-13M, [OH-]=0.60M, basic
53. pOH = 11.9, [H+]= .008M, [OH-]=1.2 x 10-12M, acidic