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U2 S2 L4 Ka and Kb calculations p 587-591: pH and Ka of a Weak Acid p 592-594: The Base Dissociation Constant, Kb Homework: p 591: # 5, 6, 7, 8, 9 and 10 p 595: # 11, 12, 13, 14, 15 and 16 p 597: # 1, 2, 3, 4, 5 and 6 p 617: # 7, 8, 10 and 11 Upon completion of this lesson, you should be able to: • calculate the value of one of Ka (or Kb) or an equilibrium concentration given all other values for a system. • calculate pH (or pOH) given the initial concentration of a weak acid (or weak base) and Ka (or Kb). • use the quadratic equation to complete Ka or Kb calculations Using percent ionization • Percent ionization data can only be used for acid concentrations of 0.10 mol/L (see note on bottom of table) Calculate the pH of a 0.10 M solution of methanoic acid. [H3O ] % ionization x 100% [HA] [H3O ] %I x [HA] 100 Finding % ionization: • A 0.15 M boric acid solution has a pH of 5.00, calculate the percent ionization of boric acid. Calculating K • A cleaning solution is prepared by dissolving ammonia in water. The equilibrium concentrations of ammonia and hydroxide found to be 0.35 mol/L and 0.0025 mol/L respectively. Calculate Kb Calculation hydronium or hydroxide using K • Propanoic acid solution has Ka = 1.3 x 10-5 and an equilibrium concentration of 0.050 mol/L. Calculate the concentration of hydronium ions and pH at equilibrium. ICE tables (brrrrrr…!) • A nitrous acid solution has an initial concentration of 0.25 mol/L. At equilibrium the hydronium concentration is 0.013 mol/L. Calculate Ka. Calculation Ka from pH • An aqueous methanoic acid solution has an initial molar concentration of 0.75 M. The pH of the solution at equilibrium is 1.95. Calculate the Ka of a methanoic acid. • An aqueous 0.50 mol/L sodium sulfite solution is prepared. The pH at equilibrium is 10.45. Calculate the Kb for the sulfite ion. Quadratic equation. • A 0.022 mol/L aspirin (acetylsalicylic acid) solution is made by dissolving a 500.0 mg tablet in about 125 mL of water. A condensed formula for aspirin is C8H7O2COOH. Given Ka for aspirin is 3.3 x 10-4, calculate the pH of the aspirin solution • Calculate the pH of a 0.50 mol/L ethanoic acid solution