AP Chemistry Unit 8 Section 4: Reactions of Acids with Bases

Introduction

• Presenter: Jeremy Krug
• Focus: Reaction of acids with bases in AP Chemistry
• Channel Content: 100+ AP Chemistry videos, problem walkthroughs, and more

Strong Acid-Strong Base Reactions

• Example: Hydrochloric acid and potassium hydroxide
• Net Ionic Equation:
  • H⁺ (aq) + OH⁻ (aq) → H₂O (l)
  • Spectator ions are typically excluded (e.g., chloride and potassium ions).

Example Problem 1

• Given: 150 mL of 0.5 M nitric acid and 300 mL of 0.3 M sodium hydroxide
• Net Ionic Equation:
  • H⁺ + OH⁻ → H₂O
• Spectator Ions: Sodium and nitrate
• pH Calculation:
  • Use moles calculation with ICE table
  • Calculate moles of each reactant, identify limiting reactant
  • Excess hydroxide results in a basic solution
  • Calculate pH using pOH = -log[OH⁻], then pH = 14 - pOH
  • Result: pH = 12.52

Example Problem 2

• Given: 290 mL of 0.2 M HBr and 185 mL of 0.5 M Ba(OH)₂
• Net Ionic Equation:
  • H⁺ + OH⁻ → H₂O
• Spectator Ions: Barium and bromide
• pH Calculation:
  • Account for stoichiometry of Ba(OH)₂ (2:1 ratio)
  • Hydroxide is limiting, resulting solution is acidic
  • Calculate pH using pH = -log[H⁺]
  • Result: pH = 2.28

Weak Acid-Strong Base Reactions

• Net Ionic Equation:
  • HA + OH⁻ → A⁻ + H₂O
  • A⁻ is the conjugate base of the weak acid
• Buffer Formation:
  • Excess weak acid and conjugate base form a buffer

Strong Acid-Weak Base Reactions

• Net Ionic Equation:
  • H₃O⁺ + B → HB⁺ + H₂O
  • HB⁺ is the conjugate acid of the weak base
• Buffer Formation:
  • Excess weak base and conjugate acid form a buffer

Understanding Acid and Base Strength

• Example 1: Cyanic acid dissociation
  • Ka is small, CN⁻ is a stronger base than water
• Example 2: Nitric acid dissociation
  • Water is a stronger base than nitrate ion

Conclusion

• Summary of acid-base reactions
• Upcoming content on acid-base titrations
• Encouragement to like and subscribe for more content