68. In water, the equilibrium 2H 2 O(l) H 3 O + (aq) + OH (aq) K c = 10 14 deter
ID: 513758 • Letter: 6
Question
68. In water, the equilibrium
2H2O(l) H3O+(aq) + OH(aq) Kc = 1014
determines the concentrations of H3O+(aq) and OH(aq). The equilibrium constant for the reaction
AgOH(s) Ag+(aq) + OH(aq) Kc = 2.0x108
shows that AgOH is not very soluble in water. At pH 10, what concentration of Ag+ (in moles/liter) is required for AgOH to start precipitating (i.e., the formation of solid AgOH).
a) 7.3x103
b) 5.3x103
* c) 2.0x104 ( the right answer)
d) 3.2x104
e) 4.9x103
Explanation / Answer
68. 2H2O(l) H3O+(aq) + OH(aq)
Kw = [H3O+][OH-]
in water [H3O+] = [OH-]
1*10-14 = [H3O+][H3O+]
[H3O+]^2 = 10^-14
[H3O+] = 10^-7M
[OH-] = 10^-7 M
AgOH(s) Ag+(aq) + OH(aq) Kc = 2.0x108
PH = 10
POH = 14-PH
POH = 14-10 = 4
-log[OH-] = 4
[OH-] = 10^-4M
Kc = [Ag+][OH-]
2*10^-8 = [Ag+] *10^-4
[Ag+] = 2*10^-8/10^-4 = 2*10^-4M
c) 2.0x104
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