Harris Chapter 7 TITRATIONS Supplements Information In Zumdahl’s Chapter 14 & 15

 Titration Nomenclature  Calculations  Precipitation Titration By regions around the Equivalence Point Titration of Mixtures  Titration Spreadsheets  End-Point Detection Supplemental Content

Titration Nomenclature  Analyte: the solution (soln.) being analyzed.  Titrant: soln. added  Equivalence point: completed reaction.  End point: measured or observed indication of change in soln.  Indicator: compound responsible for end point indication.  Standardization: fix titrant concentration with primary standard.  Back Titration: finds XS titrant to subtract.

Calculations  Buret dispenses mL of titrant, so we use mmol because M  mol / L = mmol / mL.  Burette is a diminutive of the French buire, a vase for liquors! [analyte] = (mmol analyte) / (mL initial volume) mmol analyte = (mmol titrant)  (stoichiometric ratio of analyte to titrant) mmol titrant = (mL titrant)  [titrant]  In other words, CV = CV over and over.

Precipitation Titration  Simpler than weak acid since no K w involved  (unless precipitate is an acid or base). Prior to equivalence, titrant is the limiting reactant & [analyte] = (mmol analyte – scaled mmol titrant) / (mL current solution) Post equivalence, analyte is the limiting reactant & [titrant] = (mmol titrant – scaled mmol analyte) / ( mL current solution) In either case and at equivalence:  K sp = [analyte] [titrant] (assuming 1:1)

Titration of Mixtures  Endpoints are characterized by inflection points where a curvature changes sign.  In mixtures leading to two precipitates, two inflection points are observed. The lowest K sp solid finishes its reaction by precipitating first. Thus the first inflection point. The more soluble solid precipitates last.

Spreadsheet Titration Curves  While pH is normally plotted against V titrant, the equations for V titrant = f(pH) are easier as seen in Harris The same is true if pM vs. V M is sought in precipitation titrations. n MX(s) = C° M V M – [M + ] ( V M + V° M ) n MX(s) = C° X V X – [M + ] ( V X + V° X ) (now equate) V M = V° X (C° X +[M + ]–[X – ]) / (C° M –[M + ]+[X – ])

Precipitate End-Point Detection  Volhard Titration Back titrate excess Ag + (from a halide ppt.) with SCN – in presence of Fe 3+ Red FeSCN 2+ appears after AgSCN precipitates.  Fajans Titration Won’t be used in lab., but involves coprecipitate of colored indicator at end-point.