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Harris Chapter 7. TITRATIONS Supplements Information In Zumdahl’s Chapter 14 & 15. Supplemental Content. Titration Nomenclature Calculations Precipitation Titration By regions around the Equivalence Point Titration of Mixtures Titration Spreadsheets End-Point Detection.

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harris chapter 7

Harris Chapter 7

TITRATIONS

Supplements Information

In Zumdahl’s Chapter 14 & 15

supplemental content
Supplemental Content
  • Titration Nomenclature
  • Calculations
  • Precipitation Titration
    • By regions around the Equivalence Point
    • Titration of Mixtures
  • Titration Spreadsheets
  • End-Point Detection
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.

Titration Nomenclature
calculations
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
Precipitation Titration
  • Simpler than weak acid since no Kw 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 andat equivalence:
        • Ksp = [analyte] [titrant] (assuming 1:1)
titration of mixtures
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 Ksp solid finishes its reaction by precipitating first. Thus the first inflection point.
    • The more soluble solid precipitates last.
spreadsheet titration curves
Spreadsheet Titration Curves
  • While pH is normally plotted against Vtitrant , the equations for Vtitrant = f(pH) are easier as seen in Harris 12-9. The same is true if pM vs. VM is sought in precipitation titrations.
    • nMX(s) = C°M VM – [M+] ( VM + V°M )
    • nMX(s) = C°X VX – [M+] ( VX + V°X ) (now equate)
    • VM = V°X (C°X+[M+]–[X–]) / (C°M–[M+]+[X–])
precipitate end point detection
Precipitate End-Point Detection
  • Volhard Titration
    • Back titrate excess Ag+ (from a halide ppt.) with SCN– in presence of Fe3+
    • Red FeSCN2+ appears after AgSCN precipitates.
  • Fajans Titration
    • Won’t be used in lab., but involves coprecipitate of colored indicator at end-point.