Buffers and Titration Curves
AP Chemistry
Name: _______________________________
Date: ________________________________
1)
Calculate the change in pH that occurs when 0.010 mol of solid NaOH is added to 1.0 L of
a buffered solution containing 0.50 M acetic acid (HC2H3O2, Ka = 1.8 x 10-5 M) and 0.50 M
sodium acetate (NaC2H3O2). (The pH of just the buffered solution was calculated to be 4.74.)
[ÄpH= 0.02]
Stoichiometry Problem
Equilibrium Problem
HC2H3O2 + H2O W
HC 2H 3O 2+ NaOH —> NaC 2H 3O 2 + H 2O
Before
Initial
Change
Change
After
Eq.
(b)
C2H3O2- +
H3O+
Compare this with what happens when 0.010 mol of solid NaOH are added to 1.0 L
of water to give 0.010 M NaOH. What is the change in pH?
[ÄpH = 5]
2)
Use the Henderson-Hasselbalch equation to calculate the pH of a solution containing 0.75
M lactic acid (HC3H5O3, Ka = 1.4 x 10-4) and 0.25 M sodium lactate.
[pH = 3.37]
3)
Use the Henderson-Hasselbalch equation to calculate the pH of each of the following
buffered solutions:
(a) 0.10 M acetic acid (HC2H3O2, Ka = 1.8 x 10-5) and 0.25 M sodium acetate (NaC2H3O2)
[5.14]
(b) 0.25 M acetic acid and 0.10 M sodium acetate
[4.34]
(c) 0.080 M acetic acid and 0.20 M sodium acetate
(d) 0.20 M acetic acid and 0.080 M sodium acetate (NaC2H3O2)
4)
(a)
A buffered solution contains 0.25 M NH3 (Kb = 1.8 x 10-5) and 0.40 M NH4Cl.
Calculate the pH.
[9.06]
(b)
Calculate the pH of the solution that results when 0.10 moles of gaseous HCl are
added to 1.0 L of buffer made from 0.25 M NH3 (Kb = 1.8 x 10-5) and 0.40 M NH4Cl
(in question 4a).
[8.74]
5)
Consider the acids in Table 14.2. Which acid would be the best choice to prepare a pH 7.00
buffer? Explain how to make 1.0 L of this buffer.
6)
Consider the bases in Table 14.3. Which base would be the best choice for preparing a pH
5.00 buffer? Explain how to make 1.0 L of this buffer.
7)
A titration was performed using 50.0 mL of 0.200 M HNO3 in the beaker and 0.100 M NaOH
in the buret. Calculate the pH of the solution in the beaker after the following amounts of
NaOH have been added: 0 mL, 10.0 mL, 15.0 mL, 20.0 mL, 30.0 mL, 50.0 mL, 80.0 mL and
100.0 mL.
8)
A titration was perform using 50.0 mL of 0.10 M acetic acid (HC2H3O2, Ka = 1.8 x 10-5) in
the beaker and 0.10 M NaOH in the buret. Calculate the pH of the solution in the beaker
after the following amounts of NaOH have been added: 0 mL, 10.0 mL, 15.0 mL, 20.0 mL,
25.0 mL, 40.0 mL, 50.0 mL, 60.0 mL, and 75.0 mL.
Stoichiometry Problem
Equilibrium Problem
HC2H3O2 + H2O W
HC 2H 3O 2+ NaOH —> NaC 2H 3O 2 + H 2O
Before
Initial
Change
Change
After
Eq.
Stoichiometry Problem
C2H3O2- +
H3O+
Equilibrium Problem
HC2H3O2 + H2O W
HC 2H 3O 2+ NaOH —> NaC 2H 3O 2 + H 2O
Before
Initial
Change
Change
After
Eq.
C2H3O2- +
H3O+