lecture_18_Introduction to Electroanalytical Chemistry

lecture_18_Introduction to Electroanalytical Chemistry -...

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Lecture #18 Introduction to Electroanalytical Chemistry Reading: Chapter 22, page 628 – 658 ; Problems: 22-1-17. • overview of electroanalytical chemistry • electrochemical cells; • electrode potentials; • calculation of cell potentials; • currents in electrochemical cells; Extensive reading of the chapter material is needed for understanding the different terms, some of which are easy to be confused. Practice with all examples and problems.
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Overview of electroanalytical chemistry Advantages of electroanalytical chemistry : • determination of a particular oxidation state of an element, quantitative analysis of mixture of different oxidation states of the same element, like cerium (III) and cerium (IV). • instrumentation is relatively inexpensive, ~ $5,000, compared to > $50,000 for spectroscopic instruments: • provide information about activities rather than concentrations of chemical species. Electroanalytical chemistry encompasses a group of quantitative analytical methods that are based upon the electrical properties of an analyte solution when it is made part of an electrochemical cell. Electroanalytical measurements provide information of stoichiometry and rate of interfacial charge transfer, rate of chemical reactions, rate of mass transfer, and extent of adsorption.
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Electrochemical Cells
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• Electrochemical cells consist of two electrodes: anode: the electrode at which the oxidation reaction occurs; cathode: the electrode at which the reduction reaction occurs. Zn(s) + Cu 2+ ÅÆ Zn 2+ + Cu(s) Cu 2+ + 2e - Æ Cu(s) (reduction) Zn(s) Æ Zn 2+ + 2e - (oxidation) • Schematic representation of cells: Zn ZnSO 4 ( a Zn2+ =0.0100) ⎢⎢ CuSO 4 ( a Cu2+ =0.0100) Cu Anode liquid cathode Interface junction interface • There are two types of electrochemical cells: galvanic: ones that spontaneously produce electrical energy; electrolytic: ones that consume electrical energy.
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