Overview
This lecture covers the core concepts of Acids and Bases, including their properties, key definitions, acid/base reactions, pH calculations, titrations, and important distinctions between strong/weak and concentrated/dilute solutions.
Properties and Definitions of Acids and Bases
- An acid donates H+ ions to other substances and must contain hydrogen.
- Acids react with bases, form electrolytes in solution, react with metals to produce H2 gas, turn litmus paper red, taste sour, and conduct electricity.
- A base accepts H+ ions from other substances.
- Bases react with acids, form electrolytes in solution, feel slippery, turn litmus paper blue, taste bitter, and conduct electricity.
Arrhenius and Bronsted-Lowry Definitions
- Arrhenius Acid: releases H+ in water.
- Arrhenius Base: releases OH– in water.
- Bronsted-Lowry Acid: donates H+ to another substance.
- Bronsted-Lowry Base: accepts H+ from another substance.
Acid-Base Reactions and Salts
- Acid + base → water + salt (neutralization, double replacement).
- Salt: ionic compound of a metal cation and nonmetal anion; may remain dissolved or precipitate depending on solubility.
- Net ionic equations show only ions involved in chemical change.
Strong and Weak Acids/Bases
- Strong acids/bases dissociate completely in water; weak ones establish equilibrium with reactants favored.
- Strong acid example: HCl reacts 100% with water; weak acid example: HF only partially dissociates.
- Conductivity is higher in strong acids/bases due to more ions.
Acid/Base Tables & Amphiprotic Substances
- Acids are ranked left-to-right, strongest to weakest, on tables; all strong acids dissociate 100%.
- Bases are ranked right-to-left, strongest (bottom) to weakest (top); OH– bases are strong.
- Amphiprotic substances (H2O, HCO3–, etc.) can act as either acid or base, found in both regions of the table.
Conjugate Acid-Base Pairs
- Conjugate pairs differ by one proton (H+); base has one less, acid has one more proton than its conjugate.
- Strong acids have conjugate bases that are not bases at all.
Predicting Reaction Direction
- The side with the weaker acid is always favored in equilibrium.
- Keq > 1 if products are favored; Keq < 1 if reactants are favored.
Strong/Weak vs. Concentrated/Dilute
- Strong/weak refer to extent of dissociation in water.
- Concentrated/dilute refer to molarity (amount dissolved).
Ionization of Water, pH, and Kw
- Water self-ionizes: 2H2O ⇌ H3O+ + OH–; Kw = [H3O+][OH–] = 1.0×10–14 at 25°C.
- Pure water is neutral: [H3O+] = [OH–] = 1.0×10–7 M.
- Adding acid increases [H3O+], basic increases [OH–].
- Only temperature changes the value of Keq.
pH, pOH, and Calculations
- pH = –log[H3O+]; pOH = –log[OH–]; pH + pOH = 14 at 25°C.
- Low pH (<7) = acidic; high pH (>7) = basic; pH = 7 is neutral.
- Changing pH by 1 changes [H3O+] or [OH–] by 10 times.
- pH scale can be <0 or >14 for very concentrated solutions.
Titration and Standard Solutions
- Titration: technique to determine concentration by reaction with known solution.
- At equivalence point: moles H3O+ = moles OH–; pH = 7 for strong acid/strong base.
- Calculation involves stoichiometry to find unknown concentrations.
Key Terms & Definitions
- Acid — Substance that donates H+ ions.
- Base — Substance that accepts H+ ions.
- Neutralization — Acid and base reaction producing water and salt.
- Conjugate acid/base pair — Two species differing by one H+.
- Kw — Ion product of water, 1.0×10–14 at 25°C.
- pH — Negative logarithm of [H3O+], measures solution acidity.
- Titration — Lab technique for determining concentration by neutralization.
- Amphiprotic — Acts as both acid and base.
Action Items / Next Steps
- Read and complete Hebden textbook assignments as listed in lecture (pages and questions specified throughout).
- Practice pH, pOH, and titration calculations using provided examples.
- Prepare for lab titration activities and review indicator/color change concepts.