chem

• Buffer solution


  Composed of a weak acid and the conjugate weak base
• Buffer solution


  • Maintains a constant pH level throughout the solution
  • Resists changes in its pH
• How a buffer solution maintains pH

  1. Contains both a weak acid and a weak base

  2. Weak base reacts with added acid to consume hydronium ions

  3. Weak acid reacts with added base to consume hydroxide ions
• If [base] = [acid], then pH = pKa
• Ratio of base to acid

  If ratio is 10:1, pH is 1 unit from pKa

  If ratio is 100:1, pH is 2 units from pKa

  If ratio is 1000:1, pH is 3 units from pKa
• To create a buffer solution at a desired pH, choose an acid with a pKa close to the desired pH
• Molar


  Concentration of 1 mole per liter
• Determining pH of buffer solution

  1. Keep amount of base constant

  2. Amount of acid is 10 times less than base

  3. pH will be higher than pKa
• If pH is greater than pKa


  Weak base component of buffer is greater than acid component
• If pH is less than pKa

  Acid component of buffer is greater than base component
• If pH equals pKa

  Acid and base components are equal
• Buffer solutions


  • 0.75 M acetic acid and 0.5 M sodium acetate
  • 0.15 mol ammonium chloride and 1.5 mol ammonia
  • 15 g hydrofluoric acid and 21 g sodium fluoride in 750 mL
• To calculate pKa, pKa = -log(Ka)
• pKa + pKb = 14
• To calculate pH of unknown weak acid, pH = pKa + log([base]/[acid])