9.S: Titrimetric Methods (Summary)

In a titrimetric method of analysis, the volume of titrant reacting stoichiometrically with a titrand provides quantitative information about the amount of analyte in a sample. The volume of titrant corresponding to this stoichiometric reaction is called the equivalence point. Experimentally we determine the titration’s end point using an indicator that changes color near the equivalence point. Alternatively, we can locate the end point by continuously monitoring a property of the titrand’s solution—absorbance, potential, and temperature are typical examples—that changes as the titration progresses. In either case, an accurate result requires that the end point closely match the equivalence point. Knowing the shape of a titration curve is critical to evaluating the feasibility of a titrimetric method.

Many titrations are direct, in which the analyte participates in the titration as the titrand or the titrant. Other titration strategies may be used when a direct reaction between the analyte and titrant is not feasible. In a back titration a reagent is added in excess to a solution containing the analyte. When the reaction between the reagent and the analyte is complete, the amount of excess reagent is determined by a titration. In a displacement titration the analyte displaces a reagent, usually from a complex, and the amount of displaced reagent is determined by an appropriate titration.

Titrimetric methods have been developed using acid–base, complexation, redox, and precipitation reactions. Acid–base titrations use a strong acid or a strong base as a titrant. The most common titrant for a complexation titration is EDTA. Because of their stability against air oxidation, most redox titrations use an oxidizing agent as a titrant. Titrations with reducing agents also are possible. Precipitation titrations often involve Ag⁺ as either the analyte or titrant.

9.6.1 Key Terms

acid–base titration acidity alkalinity argentometric titration asymmetric equivalence point auxiliary complexing agent auxiliary oxidizing agent auxiliary reducing agent back titration buret complexation titration conditional formation constant direct titration

displacement titration end point equivalence point Fajans method formal potential Gran plot indicator Jones reductor Kjeldahl analysis leveling metallochromic indicator Mohr method potentiometric titration

precipitation titration redox indicator redox titration spectrophotometric titration symmetric equivalence point thermometric titration titrand titrant titration curve titration error titrimetry Volhard method Walden reductor

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Contributors

David Harvey (DePauw University)