Basics of Acids and Bases

Identifying Acids and Bases

• Acids: Typically have a hydrogen in front (e.g., HCl, HF, HC2H3O2)
  • Hydrogen attached to nonmetal usually indicates an acid.
  • Positively charged hydrogen indicates an acid.
• Bases: Contain hydroxide ion (e.g., NaOH, KOH)
  • Hydrogen next to a metal (e.g., sodium hydride) indicates a base.
  • Negatively charged hydrogen indicates a base.

Definitions

Arrhenius Definition

• Acids: Release H+ ions in solution.
• Bases: Release OH- ions in solution.

Bronsted-Lowry Definition

• Acids: Proton donors.
• Bases: Proton acceptors.
  • Example: HCl in water (HCl as acid, H2O as base)

Conjugate Acids and Bases

• Conjugate Acid: Formed by adding H+ to a base.
• Conjugate Base: Formed by removing H+ from an acid.

pH Scale

• Scale ranges from 0 to 14.
• Neutral: pH = 7
• Acidic: pH < 7
• Basic: pH > 7
• pH Calculation: -log[H3O+]
• pOH Calculation: -log[OH-]
• Relationship: pH + pOH = 14 at 25°C

Strong vs Weak Acids

• Strong Acids: Ionize completely in solution (e.g., HCl, HBr)
• Weak Acids: Partially ionize; less than 5% ionization.
• Strong Acids and Bases: Form strong electrolytes.

Strong vs Weak Bases

• Strong Bases: Soluble ionic compounds, ionize completely (e.g., NaOH, KOH).
• Weak Bases: Do not ionize completely, weakly soluble (e.g., NH3).

Chemical Reactions

• Strong Acids: Use single arrow in reactions.
• Weak Acids: Use reversible reaction arrows.

Mechanisms

• Oxide Reaction: Oxide reacts with water to form hydroxide.
• Hydride Reaction: Produces hydrogen gas and hydroxide.

Properties

• Acids: Taste sour, turn blue litmus red.
• Bases: Taste bitter, feel slippery, turn red litmus blue.

Electrolytes

• Strong Acids/Bases: Conduct electricity well.
• Weak Acids/Bases: Conduct electricity poorly.

Reaction with Metals

• Acids react with active metals to produce hydrogen gas.

Additional Definitions

Lewis Definition

• Lewis Acids: Electron pair acceptors.
• Lewis Bases: Electron pair donors.

Amphoteric Substances

• Substances that can act as both acid and base (e.g., water).

Calculation Examples

• pH, pOH, [H3O+], [OH-] calculations with example values provided.

Practice Problems

• Discussed pH and pOH calculations and identifying strong/weak acids and bases.
• Reviewed acid strength in relation to Ka and pKa values.

Summary

• Strong acids have higher Ka, lower pKa.
• Strong bases have higher Kb, lower pKb.
• Acid strength inversely related to conjugate base strength.