Notes on Acids and Bases

Acids & Bases

Bronsted-Lowry Definition of Acids & Bases

• Acids: Proton donors (H+ ions).

• Bases: Proton acceptors.

• Conjugate Base: The remnants of an acid after it donates a proton.

• Conjugate Acid: The result of a base accepting a proton.

pH Scale

• Acids: pH < 7

• Bases: pH > 7

• Neutral: pH = 7

• Key Observations:

  • Lower pH values = Stronger acids.

  • Higher pH values = Stronger bases.

Salts

• Conjugates of Weak Acids: Make the pH basic.

• Conjugates of Weak Bases: Make the pH acidic.

• Strong Acids/Bases Conjugates: Result in a neutral pH.

• Determining Acidity/Basicity: Use Ka/Kb values; larger K value prevails if both weak acid and weak base conjugates are present.

Mixing Acids & Bases

Strong Acid + Strong Base

• If excess is Strong Acid:

  • Calculate molarity of leftovers.

  • Find pH from the molarity.

• If excess is Strong Base:

  • Calculate molarity of leftovers.

  • Find pOH from molarity, then calculate pH (pH = 14 - pOH).

• If equimolar: pH = 7.

Weak Acid + Strong Base

• If excess is Strong:

  • Calculate molarity of leftovers and find pH/pOH.

• If excess is Weak Acid:

  • Calculate molarity of leftover weak acid and weak product.

  • Use a RICE table for both molarities to find pH/pOH.

• If equimolar:

  • Find molarity of weak product.

  • Use a RICE table for molarity to find pH/pOH.

Acid Strength

• Oxyacids:

  • More polar or more electronegative = Stronger.

  • More halogens or oxygens = Stronger.

• Acids without oxygen:

  • Larger ions (atomic radii) are stronger.

pK Values

• Small pKa = Large Ka = Strong Acid.

• Small pKb = Large Kb = Strong Base.

• pK can be determined at half-equivalence point on a titration curve.

Water Ionization

• Water auto-ionizes: Kw = 1 x 10^-14 = [H3O+][OH-].

• Relationship:

  • If known

  • [H3O+]: Calculate pH = -log[H3O+].

  • [OH-]: Calculate pOH = -log[OH-].

  • pH + pOH = 14.

  • Kw = 1 x 10^-14 = Ka x Kb.

Concentrations of Acids and Bases

• Acids: Form [H3O+] in solution.

• Bases: Form [OH-] in solution.

• Strong Bases: [OH-] equals formula containing 1 OH ion.

• Strong Acids: [H3O+] equals formula containing 1 H ion.

• Weak Acids/Bases: Equilibria established; [Weak] does not equal [H3O+] or [OH-].

Strong Acids & Strong Bases

• Common Strong Acids:

  • HCl, HBr, HI, H2SO4, HNO3, HClO4.

• Common Strong Bases:

  • LiOH, NaOH, KOH, Ca(OH)2, etc.

• Characteristics:

  • Strong acids and bases fully dissociate, high K constants, and weak conjugates.

  • Weak acids and bases barely dissociate, low K constants.

Miscellaneous Vocabulary

• Anhydride: Substance without hydrogen that forms acids/bases in water.

• Acid Anhydride: Non-metal oxide that makes water acidic.

• Basic Anhydride: Metal oxide that makes water basic.

• Coordinate Covalent Bonds: Both electrons provided by one atom.

• Complex Ion: Metal cation forming coordinate covalent bonds with water.

• Polyprotic: Acid with multiple hydrogen ions.

• Amphiprotic/Amphoteric: Substance acting as both an acid and a base.

• Common Strong Acids:

  • HCl

  • HBr

  • HI

  • H2SO4

  • HNO3

  • HClO4