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Marisa Carlson Lizzie Sokol AP exam review Acid Base Stoichiometry and Titrations Stoichiometry In an acid, HxA, or base, B(OH)x, x determines the number of equivalence points in the titration. What is a Titration? A procedure for quantitative analysis of a substance by an essentially complete reaction in solution with a measured quantity of a reagent of known concentration. Finding Equivalence Points n1V1C1 = n2V2C2 n is the number of moles of H+ or OH- in the acid and base to be titrated and/or to titrate C is the concentration of the acid and base V is the volume, one quantity is given, the other one is unknown and determines how much titrant is needed to reach the first equivalence point (all number relating to acid go on one side, and all relating to base go on the other) Basic Steps to solving titration problems Use ice charts to determine equilibrium concentrations Write the equilibrium expression and set equal to Ka or Kb Solve for unknown concentration(s) Take the –log(concentration of H+ or OH-) to find pH or pOH If pOH is found, subtract from 14 to find pH If solving for the pH at an equivalence point, be sure to check whether the Ka or the Kb should be used (the greater quantity is more prominent and therefore should be used) Kb= 1x10-14 / Ka Helpful Hints You can use the concentration of the acid or base in the ice chart as long as the concentrations of both products are unknown. pH= pKa + log([A-]/[HA]) pOH= pKb + log ([HB+]/[B]) Remember that the pH of a solution after the acid or base has been completely neutralized does not require an ice chart. When deciding whether to use the Ka or the Kb, use Kbn-1 compared to Kan Titrating a Base with an Acid Virtually no difference except: when solving for x, x= [OH-] so, when the -log(x) is taken, the result is the pOH therefore, to find the pH, subtract pOH from 14