Transcription of Lecture 10 - Redox Titrations - Cal State LA
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Lecture 10 - Redox Titrations - Cal State LA
Redox Titrations -the oxidation/ reduction reaction between analyte and titrant -titrants are commonly oxidizing agents, although reducing titrants can be used -the equivalence point is based upon: Aox + Bred ! Ared + Box Rx n goes to completion after each addition of titrant Potentiometric Titration: Titration reaction: Ce4+ + Fe2+ ! Ce3+ + Fe3+ (1) Reference half-reaction: 2Hg(l) + 2Cl- ! Hg2Cl2(s) + 2e- At the Pt indicator electrode (Indicator half-reaction) Fe3 + e- !Fe2+ E0 = V (2) Ce4+ + e- !Ce3+ E0 = (3) Cell reactions (in 1 M HClO4): 2Fe3+ + 2Hg(l) + 2Cl- !2Fe2+ + Hg2Cl2(s) (4) 2Ce4+ + 2Hg(l) + 2Cl- ! 2Ce3+ + Hg2Cl2(s) (5) Relationships - Cell reactions are not the same as the titration reaction - May describe the cell voltage with either (4) or (5) or both Balancing Redox Reactions Balance: -atoms -# of electrons transferred Example: Cr(s) + Ag+ !
b. Oxidation-reduction indicators- respond to the potential of the system rather than to the appearance or disappearance of some species during the course of the titration, e.g. methylene blue Color changes will occur over the range: Volts n EE) 0.05916 =(0± where n= # of electrons in the indicator half-reaction
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