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13: Kinetic Methods

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  • There are many ways to categorize analytical techniques, several of which we introduced in earlier chapters. In Chapter 3 we classified techniques by whether the signal is proportional to the absolute amount or the relative amount of analyte. For example, precipitation gravimetry is a total analysis technique because the precipitate’s mass is proportional to the absolute amount, or moles, of analyte. UV/Vis absorption spectroscopy, on the other hand, is a concentration technique because absorbance is proportional to the relative amount, or concentration, of analyte.

    A second method for classifying analytical techniques is to consider the source of the analytical signal. For example, gravimetry encompasses all techniques in which the analytical signal is a measurement of mass or a change in mass. Spectroscopy, on the other hand, includes those techniques in which we probe a sample with an energetic particle, such as the absorption of a photon. This is the classification scheme used in organizing Chapters 8–11.

    Another way to classify analytical techniques is by whether the analyte’s concentration is determined by an equilibrium reaction or by the kinetics of a chemical reaction or a physical process. The analytical methods described in Chapter 8–11 mostly involve measurements made on systems in which the analyte is always at equilibrium. In this chapter we turn our attention to measurements made under non-equilibrium conditions.

    • 13.1: Kinetic Methods Versus Equilibrium Methods
      In an equilibrium method the analytical signal is determined by an equilibrium reaction involving the analyte or by a steady-state process that maintains the analyte’s concentration. In a kinetic method the analytical signal is determined by the rate of a reaction involving the analyte, or by a nonsteady-state process. As a result, the analyte’s concentration changes during the time in which we are monitoring the signal.
    • 13.2: Chemical Kinetics
      Every chemical reaction occurs at a finite rate, making it a potential candidate for a chemical kinetic method of analysis. To be effective, however, the chemical reaction must meet three necessary conditions: the reaction must not occur too quickly or too slowly; we must know the reaction’s rate law; and we must be able to monitor the change in concentration for at least one species.
    • 13.3: Radiochemistry
      Atoms having the same number of protons but a different number of neutrons are isotopes. Although an element’s different isotopes have the same chemical properties, their nuclear properties are different. The most important difference between isotopes is their stability. The nuclear configuration of a stable isotope remains constant with time. Unstable isotopes, however, spontaneously disintegrate, emitting radioactive particles as they transform into a more stable form.
    • 13.4: Flow Injection Analysis
      The flow injection analysis (FIA) technique involves injecting the sample into a flowing carrier stream that gives rise to a transient signal at the detector. Because the shape of this transient signal depends on the physical and chemical kinetic processes occurring in the carrier stream during the time between injection and detection, we include flow injection analysis in this chapter.
    • 13.E: Kinetic Methods (Exercises)
      These are homework exercises to accompany "Chapter 13: Kinetic Methods" from Harvey's "Analytical Chemistry 2.0" Textmap.
    • 13.S: Kinetic Methods (Summary)
      This is a summary to accompany "Chapter 13: Kinetic Methods" from Harvey's "Analytical Chemistry 2.0" Textmap.

    Thumbnail: Determination of a reaction’s intermediate rate from the slope of a line tangent to a curve showing the change in the analyte’s concentration as a function of time.