chap 16

• Strong acid


  Completely dissociates in aqueous solution
• Strong base


  Completely dissociates in aqueous solution
• Weak acid


  Partially dissociates in aqueous solution
• Weak base


  Partially dissociates in aqueous solution
• Ka


  Acid ionization constant
• Kb


  Base ionization constant
• Conjugate acid-base pair


  Acid and its conjugate base, or base and its conjugate acid
• Calculating Ka and Kb from equilibrium concentrations


  1. Write the equilibrium expression

  2. Substitute equilibrium concentrations

  3. Solve for Ka or Kb
• Salts can also act as acids or bases
• Predicting the acid or base characteristics of a salt


  1. Identify the conjugate acid-base pairs

  2. Determine the relative strengths of the acid and base

  3. Predict the acid/base behavior of the salt
• Water undergoes self-ionization or autoionization making it a weak electrolyte
• Ion product of water, Kw


  [H+][OH-] = 1.0 x 10^-14 (at 25°C)

  
• In any aqueous solution, the product of [H+] and [OH-] equals Kw
• Neutral solutions: [H3O+] = [OH-] or [H+] = [OH-]
• Acidic solutions: [H3O+] > [OH-] or [H+] > [OH-]
• Basic solutions: [H3O+] < [OH-] or [H+] < [OH-]
• Neutral solutions: pH = 7.00
• Acidic solutions: pH < 7.00
• Basic solutions: pH > 7.00
• pH + pOH = pKw = 14.00 (at 25°C)
• Autoionization of water is suppressed in strongly acidic or strongly basic solutions
• Autoionization of water contributes negligibly to [H+] in solutions greater than 10^-6 M
• Weak acids partially ionize in aqueous solution
• Stronger acids have larger Ka values and smaller pKa values
• KaKb = Kw for a conjugate acid-base pair
• The stronger the acid, the weaker the conjugate base
• The primary goal is to determine the equilibrium constant and concentrations
• The percentage ionization of the acid or base is also routinely calculated
• Kb


  Equilibrium constant for a weak base
• Kw = Ka × Kb


  Relationship between equilibrium constants for weak acids and bases
• Determining Kb from given Ka

  Kb = Kw/Ka
• Morphine is a weak base
• Determining Kb, pKb, and percentage ionization of morphine


  1. Given 0.010 M solution has pH of 10.10

  2. Use Kw = [H+][OH-] to find [OH-]

  3. Calculate Kb, pKb, and % ionization
• Calculating Ka for butyric acid


  Use Ka = [H3O+][A-]/[HA] and given information to solve for Ka
• Determining pH of 0.1 M solutions


  1. For weak base N2H4 (Kb=1.7×10-6)

  2. For weak base NH3 (Kb=1.8×10-5)
• Nitrous acid (HNO2) has varying % ionization and equilibrium concentrations at different initial concentrations
• NH4+


  Weak acid, conjugate acid of weak base NH3
• NO2-


  Weak base
• Determining pH of 0.10 M NaNO2 solution


  Use Kb = Kw/Ka for HNO2 to find [OH-] and calculate pH
• Acid/base/neutral or amphoteric properties of 0.1 M solutions


  • HCl (acid)
  • NaCl (neutral)
  • NaCN (base)
  • HCN (acid)
  • Na2S (base)
  • Na3PO4 (base)
  • NH4Cl (acid)