Acid/Base Workshop Sheet Stuff
Consider a base, B. B is a weak base. B is a good base. A very good base.
1a) write the reaction that will occur when this base reacts with water.
B + H2O « BH+ + OH-
b) write the reaction that will occur when B reacts with nitric acid. What products are generated?
B + H3O+« BH+ + H2O
d) Imagine 0.05 mol of B are dissolved in 1.00 L of water. If the pH of the solution is 11.63, what is the Kb of B? What is the Ka of its conjugate acid?
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x = 7.07 ´ 10-7.
pH = -log [H3O+] = 6.15
f) What would be the pH of a solution that contained 0.025 mol of
B and 0.005 mol of its conjugate acid in 500 mL?
g) What would be the pH of the above solution if some joker poured 100
mL of 0.1 M HCl into it?
2. Imagine a diprotic base, B2-. Write the first and second base ionization reactions of B2-. If Kb1 = 3.5 ´ 10-4 and Kb2 = 2.0 ´ 10-8, what would be the values of Ka for the species H2B?
B2- + H2O « HB- + OH- K = Kb1
HB- + H2O « H2B + OH- K = Kb2
The reactions of H2B are:
HB- + H2O « H2B + OH- K = Ka2 = Kw/Kb1 = 2.9 ´ 10-11
a) what would be the pH of a 50 mL sample of 0.100 M H2B?
Treat as a monoprotic acid with Ka = 5.0 ´ 10-7
x = [H3O+] = 2.2 ´ 10-4 pH = 3.65
b) what would be the pH after 25 mL of 0.100 M NaOH are added to
the solution above?
c) After 50 mL are added?
This is a solution of the amphoteric compound, HB+.
d) After 75 mL are added?
e) After 100 mL are added?
Treat as a monoprotic base with Kb = 3.5 ´ 10-4
x = [OH-] = 3.23 ´ 10-3 pH = 11.51
f) After 125 mL are added?
25 mL excess 0.100 M NaOH have been added. Thus, [OH-] = 0.0143; pH = 12.15.