Overview
This lecture covers the fundamentals of acids and bases, including their identification, key definitions, chemical properties, pH calculations, and common exam questions.
Identifying Acids and Bases
- Acids usually have hydrogen (H) at the front of their formula, e.g., HCl, HF.
- Bases typically contain hydroxide (OH⁻), e.g., NaOH, KOH.
- Hydrogen bonded to a metal (e.g., NaH) is a base, not an acid.
- Acids release H⁺ (hydrogen ions); bases release OH⁻ (hydroxide ions).
Definitions of Acids and Bases
- Arrhenius Acid: Releases H⁺ ions in solution.
- Arrhenius Base: Releases OH⁻ ions in solution.
- Brønsted-Lowry Acid: Proton donor.
- Brønsted-Lowry Base: Proton acceptor.
- Lewis Acid: Electron pair acceptor.
- Lewis Base: Electron pair donor.
Conjugate Acids and Bases
- The conjugate acid is formed by adding H⁺ to a base.
- The conjugate base is formed by removing H⁺ from an acid.
- Acid turns into conjugate base; base turns into conjugate acid during reactions.
- Amphoteric substances (like water, H₂PO₄⁻) can act as acid or base.
pH, pOH, and Calculations
- pH = –log[H₃O⁺]; pOH = –log[OH⁻].
- pH + pOH = 14 at 25°C.
- [H₃O⁺] = 10^(–pH); [OH⁻] = 10^(–pOH).
- Acidic pH: < 7; Neutral: 7; Basic: > 7.
Strong vs. Weak Acids and Bases
- Strong acids (e.g., HCl, HNO₃, H₂SO₄) ionize completely; weak acids ionize <5%.
- Strong bases (e.g., NaOH, KOH) are fully soluble; weak bases (e.g., NH₃, Al(OH)₃) ionize <1%.
- Strong acids/bases are strong electrolytes; weak acids/bases are weak electrolytes.
Acid-Base Equilibrium and Constants
- Kₐ (acid dissociation constant) measures acid strength; higher Kₐ = stronger acid.
- pKₐ = –log Kₐ; lower pKₐ = stronger acid.
- Kb (base dissociation constant) and pKb = –log Kb for bases.
- Kₐ × Kb = Kw = 1 × 10⁻¹⁴ at 25°C.
Trends and Properties
- More oxygen atoms in oxyacids = stronger acid.
- Acids taste sour, turn blue litmus red, react with active metals to produce H₂ gas.
- Bases taste bitter, feel slippery, turn red litmus blue.
Practice Problems & Key Relationships
- pH and pOH calculations from ion concentrations.
- Stronger acid = weaker conjugate base and vice versa.
- Acid/base strengths linked to Kₐ, Kb, pKₐ, and pKb values.
Key Terms & Definitions
- Acid — substance that donates H⁺ ions/protons or accepts an electron pair.
- Base — substance that accepts H⁺ ions/protons or donates an electron pair.
- pH — negative logarithm of H₃O⁺ concentration.
- Conjugate Acid/Base — product of acid/base after donating/accepting H⁺.
- Amphoteric — can act as both acid and base.
- Kₐ/Kb — acid/base dissociation constant.
- Kw — ion product of water, Kw = 1 × 10⁻¹⁴ at 25°C.
- Strong/Weak Electrolyte — substance that ionizes completely/partially in solution.
Action Items / Next Steps
- Add all provided equations to your notes for reference.
- Practice pH/pOH and conjugate acid/base calculations.
- Review the list of strong acids and bases for memorization.