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Harris Chapter 7. TITRATIONS Supplements Information In Zumdahl’s Chapter 14 &amp; 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

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
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
• 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 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
• 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
• 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
• 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.