Practice: Determine the pH of a solution made by dissolving 6.1 g of sodium cyanide, NaCN, in enough water to make a 500.0 mL of solution. (MW of NaCN = 49.01 g/mol). The Ka value of HCN is 4.9 × 10−10.
Weak Bases partially ionize or dissociate when placed in a solution
Calculating pH
Concept #1: Weak Bases require an ICE Chart to determine their pH.
Example #1: Calculate the hydroxide ion concentration of a 0.55 M KF solution at 25ºC. The acid dissociation constant of HF is 3.5 x 10-4.
Example #2: What is the pH of a 0.12 M ethylamine, C2H5NH2, solution? The Kb value of ethylamine is 5.6 x 10-4.
Concept #2: Weak Bases are weak electrolytes and so will ionize less than 100%.
Example #3: Calculate the percent ionization when 73.2 g sodium hypoiodite, NaIO, are dissolved with 500 mL of solution. The Ka value of hypoiodous acid, HIO, is 2.3 x 10-11.
Practice: An unknown weak base has an initial concentration of 0.750 M with a pH of 8.03. Calculate its equilibrium base constant.
