AP Chemistry: Acids and Bases

Introduction

• Apologies for the delay in video release.
• The focus is on Unit 8: Acids and Bases.
• Video is part of a series to complete the AP Chemistry course.

Basic Definitions

Arrhenius Definition

• Acid: Releases H⁺ ions (hydrogen ions/protons).
• Base: Releases OH⁻ ions (hydroxide ions).
• Important to know the Arrhenius definition.
• H⁺ and H₃O⁺ (hydronium ion) are used interchangeably.

Neutralization Reactions

• Acid + Base → Water + Salt
• Example: HCl + NaOH → H₂O + NaCl
• Net ionic equation for all neutralization reactions: H⁺ + OH⁻ → H₂O

pH and pOH

pH Scale

• pH measures acidity/basicity:
  • pH < 7: Acidic
  • pH = 7: Neutral
  • pH > 7: Basic
• Formula: pH = -log[H⁺]

Calculating Examples

• If [H⁺] = 10⁻⁵, pH = 5.
• Use the formula for non-base-10 values with a calculator.

pOH

• Formula: pOH = -log[OH⁻]
• Relationship: pH + pOH = 14

Strong and Weak Acids/Bases

Strong Acids and Bases

• Strong acids dissociate completely.
• Examples: H₂SO₄, HNO₃, HClO₄, HCl
• Strong bases: NaOH, KOH

Weak Acids and Bases

• Do not fully dissociate.
• Example: Acetic acid (HC₂H₃O₂)

Bronsted-Lowry Definition

• Acid: Donates H⁺ ions.
• Base: Accepts H⁺ ions.
• Water can act as both an acid and a base (amphoteric).

Acid-Base Equilibria

Equilibrium Constants

• Ka: Acid dissociation constant.
• Kb: Base dissociation constant.
• Larger Ka/Kb indicates stronger acid/base.

Ice Charts

• Use initial, change, and equilibrium concentrations to calculate.

Henderson-Hasselbalch Equation

• Useful for buffer solutions:

  [ \text{pH} = \text{pK}a + \log \frac{[A^-]}{[HA]} ]

Buffers

• Resist changes in pH when acids/bases are added.
• Made from a weak acid and its conjugate base.

Titration

Strong Acid-Strong Base Titration

• Equivalence point at pH 7

Weak Acid-Strong Base Titration

• Buffer effect changes the pH curve.
• Use Henderson-Hasselbalch equation initially.

Summary

• Understanding the definitions, pH/pOH calculations, and equilibria are crucial.
• Be familiar with strong and weak acids/bases and their properties.
• Practice buffer and titration calculations for exams.