Tro Chapter 16 - Aqueous Ionic Equilibria
•  Buffers
•  Acid-Base Titrations
•  Solubility Equilibria and the Solubility Product Constant, Ksp
•  Skip section 16.7 & 16.8
Suggested eoc problems: 33, 37, 41, 49, 53, 67, 71, 73, 87, 89, 91, 93, 101, 103
Tro 16.2
Buffers: Solutions that resist pH change
Calculating the pH of a buffer solution
Solution #1 : 0.500 M CH3COOH and 0.500 M CH3COONa; calculate pH
Calculate the pH following the addition of 0.02 mol of NaOH to 1.0 L of solution #1
Calculate the pH following the addition of 0.020 mol of HCl to 1.0 L of solution #1
Buffer’s continued
An environmental chemist needs a carbonate buffer of pH
10.00 to study the effects of acid rain on limestone-rich
soils. How many grams of Na2CO3 must she add to 1.5 L of
freshly prepared 0.20 M NaHCO3 to make the buffer (Ka of
HCO3- = 4.7 x 10-11)
Tro 16.3
Buffer Effectiveness
Preparing a buffer from benzoic acid and sodium benzoate
How many grams of benzoic acid (C6H5COOH) should be
added to 5.0 L of 0.050 M sodium benzoate
(C6H5COONa) to make a pH 4.25 buffer? The Ka for
benzoic acid is 6.3 x 10-5.
Tro 16.4
Acid-base titrations and pH curvers
Reaction of a:
1) STRONG acid + STRONG base
2) STRONG base + weak acid
3) STRONG acid + weak base
CH3COOH/CH3COO- buffer with different
concentrations; chart shows how pH
changes following addition of a given
amount of strong base
A/B titrations are used to determine Ka values for new
compounds and to quantitate acids and bases
Strong Acid-Base Titration Curve
Weak Acid-Strong base titration curve
Calculate pH at
0 mL NaOH added
20 mL NaOH added
40 mL NaOH added
50 mL NaOH added
Weak Base-Strong acid titration curve
Calculate pH at
0 mL HCl added – pH = 11.125
20 mL HCl added – pH = 9.25
40 mL HCl added – pH = 5.27
50 mL HCl added – pH = 1.95
Weak Polyprotic Acid-Strong base titration curve
Tro 16.5
Solubility equilibria
Tro 16.5
Solubility equilibria and the solubility product constant Ksp
• Writing Ksp expressions
• Calculating solubility
• Factors affecting solubility
Problems involving sparingly soluble salts
Lead sulfate (PbSO4, MW 303.3) is a key component of
lead-acid car batteries. Its solubility in water at 25˚C is
4.25 x 10-3 g/100 mL solution. What is the Ksp of PbSO4?
Calcium hydroxide is major component of mortar,
plaster and cement, and solutions of Ca(OH)2 are used
in industry as a cheap, strong base. Calculate the
solubility of Ca(OH)2 in water if the Ksp is 6.5 x 10-6.
Solubility and the common ion effect
What is the solubility of Ca(OH)2 in 0.10 M
Ca(NO3)2? The Ksp for Ca(OH)2 is 6.5 x 10-6.
Would addition of H3O+ affect the solubility of
a)  Lead (II) bromide
b)  Copper (II) hydroxide
c)  Iron (II) sulfide
Tro 16.6
Precipitation and Qsp - the ion product
Will a precipitate form when 0.100 L of 0.30 M
Ca(NO3)2 is mixed with 0.200 L of 0.060 M NaF?
Ksp for CaF2 = 3.2 x 10-11