common-ion effect - ionization of electrolyte decreases if common ion added  

• shifts equilibrium against a certain side
• Ka = [H+][common ion] / [acid]
• Kb = [OH-][common ion] / [base]
• can decrease the solubility of certain slightly soluble salts

Find the pH in a solution of 0.1 M lactic acid and 0.1 M sodium lactate  

• Given:
  • Ka of lactic acid = 1.4 x 10-4
  • Ka = [H+][common ion] / [acid]
• 1.4 x 10-4 = [H+] x 0.1 / 0.1
• 1.4 x 10-4 = [H+]
• pH = -log [H+] = 3.85

Find the pH of a 500mL solution containing 1.00 g propionic acid and 1.0 g sodium propionate  

• Given:
  • Ka of propionic acid = 1.3 x 10-5
  • propionic acid = HC3H5O2
  • sodium propionate = NaC3H5O2
  • Ka = [H+][common ion] / [acid]
• [propionic acid] = 1 / (1+36+5+32) / 0.5 = 0.027
• [sodium propionate] = 1 / (23+36+5+32) / 0.5 = 0.0208
• 1.3 x 10-5 = [H+] [sodium propionate] / [propionic acid]
• [H+] = 1.68 x 10-5
• pH = -log[H+] = 4.77

complex ions - made up of metal ion and Lewis base  

• stability depends on equilibrium constant for its formation
• metal ions act as electron-pair acceptors, Lewis acids
• metal salts can dissolve more easily when metal ion can react w/ the solvent

amphoterism - able to act as acid or base  

• includes hydroxides, oxides of Al3+, Cr3+, Zn2+, Sn2+
• contains basic anions >> dissolves in acidic solutions
• can form complex ions >> dissolves in basic solutions

precipitation/separation of ions - occurs when product of ion concentrations > Ksp  

• equilibrium = saturation
• selective precipitation - uses reagent to form a precipitate w/ 1 of the ions
• insoluble chlorides - formed from Ag+, Hg22+, Pb2+
• acid-insoluble sulfides - CuS, Bi2S3, CdS, PbS, HgS, As2S3, Sb2S3, SnS2
• base-insoluble sulfides/hydroxides - formed from Al3+, Cr3+, Fe3+, Zn2+, Ni2+, Co2+, Mn2+
• insoluble phosphates - formed from Mg2+, Ca2+, Sr2+, Ba2+
• alkali meta ions - remainder of possible metal ions, can be tested for individually