APCHEM - UNIT 8: Acids and Bases

  • Acids: Substances that can donate protons (H+) and typically have a sour taste.

  • Bases: Substances that can accept protons or donate hydroxide ions (OH-) and usually feel slippery.

8.1 Intro to Acids and Bases

Essential Knowledge Statements:

  • The concentrations of hydronium ion and hydroxide ion are often reported as pH and pOH, respectively

    • EQN: pH = -log[H3O+]

    • EQN: pOH = -log[OH-]

  • The terms “hydrogen ion and “hydronium ion” and the symbols H+ (aq) and H3O+ (aq) are often used interchangeably for the aqueous ion of hydrogen

  • Water autoionizes with an equilibrium constant Hw

    • EQN: Kw = [H3O+][OH-] = 1.0×10-14 at 25 degrees

  • In pure water, pH = pOH is called a neutral solution. At 25 degrees, pKw = 14.0 and thus pH = pOH = 7.0

    • EQN: pKw = 14 = pH + pOH at 25 degrees

  • The value of Kw is temperature dependent, so the pH of pure, neutral water will deviate from 7.0 at temperatures other than 25 degrees

  • Strong acid is a dissociation while weak acid is an ionization

    • this is because weak acids and bases incompletely dissociate in water

  • Equilibrium reactions:

    • HA + B- → HB+ + A-

      HB+: conjugate acid of B-

      A-: conjugate base of HA

      • Conjugate acid: formed when a base accepts a proton

      • Conjugate base: what remains after an acid has donated its proton

  • Strong Acids: HCl, HBr, HI, HClO4, HNO3, H2SO4

  • Strong Bases: LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

  • A lower Ka corresponds to a weaker acid