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

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)

Buffer’s continued 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.

CH3COOH/CH3COO- buffer with different concentrations; chart shows how pH changes following addition of a given amount of strong base

Tro 16.3 Buffer Effectiveness Acid-base titrations and pH curvers

Reaction of a:

1) STRONG acid + STRONG base

2) STRONG base + weak acid

3) STRONG acid + weak base

A/B titrations are used to determine Ka values for new compounds and to quantitate acids and bases

Tro 16.4

Strong Acid-Base Titration Curve

Calculate pH at

0 mL NaOH added

20 mL NaOH added

40 mL NaOH added

50 mL NaOH added

Weak Acid-Strong base 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 Base-Strong acid titration curve Weak Polyprotic Acid-Strong base titration curve

Solubility equilibria Tro 16.5 Solubility equilibria and the solubility product constant Ksp

• Writing Ksp expressions

• Calculating solubility

• Factors affecting solubility

Tro 16.5

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.

Problems involving sparingly soluble salts

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.

Solubility and the common ion effect

Would addition of H3O+ affect the solubility of

a)  Lead (II) bromide

b)  Copper (II) hydroxide

c)  Iron (II) sulfide

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

Tro 16.6