Upcoming Deadlines

• ALEKS Chapter 18 Due: Wednesday (potential extension to Friday)

• Chapters Covered: Seventeen, Eighteen, and Nineteen

• Additional Information: To be shared later this week

Topic Overview

• Focus for Today:

  • Quantifying the pH of polyprotic acid solutions

  • pH of salts

  • Buffer solutions defined in Chapter 19

Acid-Base Calculations

• Previously discussed calculating pH from hydroxide and the given Kb: 1.62 x 10⁻⁵

• Example Solution: 0.1 M Sodium Cyanide

• Question posed: Will the solution be acidic or basic at equilibrium?

• Discussion centered on equilibrium reactions

  • For sodium cyanide, the reaction produces hydrocyanic acid

  • Effects on hydrocyonium (H₃O⁺) and hydroxide (OH⁻) balance discussed

Key Concepts

• Equilibrium Constants:

  • Relationship derived from Kw = Ka x Kb influenced the equilibrium concentrations

• Deprotonation of Diprotic Acids:

  • Example: Oxalic Acid (C₂O₄) as a diprotic carboxylic acid

  • First deprotonation (Ka₁: 5.6 x 10⁻²) primarily contributes to H₃O⁺ concentration while further deprotonation (Ka₂: 5.4 x 10⁻⁵) is less significant

Biological Relevance of Oxalic Acid

• Oxalate's role in binding calcium and forming kidney stones

• Common Oxalate-rich Foods: Spinach, Taro

Step-by-Step for Calculating pH of Oxalic Acid

1. Gather Ka values:

   • Ka₁ = 5.6 x 10⁻²

   • Ka₂ = 5.4 x 10⁻⁵

2. Identify species concentrations at equilibrium:

   • Fully protonated oxalic acid

   • Hydrogen oxalate ion concentration found through calculations

   • Notable that concentration of oxalate is determined through Ka₂

3. Real-life implications suggest two calculations for completeness, but class problems simplify focus to significant contributions

Acid-Base Characteristics of Salts

• Neutral Solutions:

  • Salts from strong acids/bases fully dissociate

  • e.g. Sodium Acetate

• Basic Solutions:

  • Alkali metal salts, with weak acids, produce hydroxide.

  • Example: KCN (Potassium Cyanide)

• Acidic Solutions:

  • Salts formed from weak bases and strong acids lead to acidic solutions.

  • Example: Ammonium Chloride (NH₄Cl)

Reaction Mechanisms

• Discussed dissociation/effects causing hydrolysis and implications on pH

• Reference for future chapters includes precipitation reactions with metallic ions

Closing Remarks

• All salts exhibit dissociation; however, their subsequent reactions with water determine if they yield acidic, basic, or neutral solutions

• Memorization of strong acids/bases required; tables of salts will be provided during the midterm for reference

• Importance in understanding behavior of acids and bases in various reactions and solving equilibrium focuses in complex systems.