Untitled - Kelly Walsh High School

Buffers and Other Equilibria 249
The common-ion effect is an application of Le Châtelier’s principle to equilibrium
systems of slightly soluble salts. A buffer is a solution that resists a change
in pH if we add an acid or base. We can calculate the pH of a buffer using the
Henderson-Hasselbalch equation. We use titrations to determine the concentration
of an acid or base solution. We can represent solubility equilibria by the
solubility product constant expression, K sp. We can use the concepts associated
with weak acids and bases to calculate the pH at any point during a titration.
1. Write the Henderson-Hasselbalch equation for pH and for pOH.
2. Complete the following table for use with buffer solutions:
[HA] [A ]
HNO2 _____
_____
HCO3 _____
CH3NH3 NH3 _____
2 HPO4 _____
3. Write equilibrium constant expressions (K sp) for the addition of each of the
following substances to water.
a. AgBr b. Ag 2SO 4 c. AlF 3 d. CaCO 3 e. Ca 3(PO 4) 2
4. Write an equilibrium constant expression (K f) for the formation of the
Ag(NH 3) 2 ion.
5. Calculate the molar solubility of calcium carbonate, CaCO 3 that will dissolve
in each of the following. The K sp for calcium carbonate is 8.7 10 9 .
a. in pure water b. in 6.5 10 2 M Ca 2 c. in 0.35 M CO 3 2 solution.
6. Determine the pH of each of the following buffer solutions.
a. 0.15 M HC 2H 3O 2 and 0.15 M C 2H 3O 2 with pKa 4.76
b. 0.25 M NH 3 and 0.30 M NH 4 with pKb 4.76
c. 1.0 M HF and 0.75 M F with K a 6.8 10 4
d. 1.2 M C 5H 5N and 0.75 M HC 5H 5N with K b 1.5 10 9
e. 0.60 M HCO 3 and 0.80 M CO3 2 with pKa1 6.35 and pK a2 10.32
7. The pH of a 50.00-mL sample of 0.06000 M strontium hydroxide is measured
as it is titrated with a 0.1200 M hydrochloric acid. Determine the pH of the
solution after the following total volumes of hydrochloric acid have been
added.
a. 0.00 mL b. 25.00 mL c. 50.00 mL d. 75.00 mL
8. The pH of a 50.00-mL sample of 0.1100 M ammonia, NH 3, is measured as it
is titrated with a 0.1100 M hydrochloric acid, HCl. Determine the pH of the
solution after the following total volumes of hydrochloric acid have been
added.
a. 0.00 mL b. 25.00 mL c. 50.00 mL
d. 75.00 mL (K b for NH 3 is 1.76 10 5 .)