Coulometry electrogravimetry

Analytical methods based upon oxidation/reduction reactions include oxidation/reduction titrimetry, potentiometry, coulometry, electrogravimetry and voltammetry. Faradaic oxidation/reduction equilibria are conveniently studied by measuring the potentials of electrochemical cells in which the two half-reactions making up the equilibrium are participants. Electrochemical cells, which are galvanic or electrolytic, reversible or irreversible, consist of two conductors called electrodes, each of which is immersed in an electrolyte solution. In most of the cells, the two electrodes are different and must be separated (by a salt bridge) to avoid direct reaction between the reactants. 

W e now turn our attention to several analytical methods that are based on oxidation/reduction reactions. These methods, which are described in Chapters 18 through 23, include oxidation/reduction titrimetry, potentiometry, coulometry, electrogravimetry, and voltammetry. Fundamentals of electrochemistry that are necessary for understanding the principles of these procedures are presented in this chapter. 

See also. Amperometry. Conductimetry and Oscillometry. Coulometry. Electrogravimetry. Ion-Selective Electrodes Oven/iew Glass Solid-State Liquid Membrane Gas Sensing Probes Water Applications. pH. Polarography Overview. Process Analysis Sensors. Sensors Overview Amperometric Oxygen Sensors. Sulfur. Voltammetry Overview Anodic Stripping. Water Analysis Industrial Effluents. 

Electrical methods of analysis (apart from electrogravimetry referred to above) involve the measurement of current, voltage or resistance in relation to the concentration of a certain species in solution. Techniques which can be included under this general heading are (i) voltammetry (measurement of current at a micro-electrode at a specified voltage) (ii) coulometry (measurement of current and time needed to complete an electrochemical reaction or to generate sufficient material to react completely with a specified reagent) (iii) potentiometry (measurement of the potential of an electrode in equilibrium with an ion to be determined) (iv) conductimetry (measurement of the electrical conductivity of a solution). 

The main electroanalytical techniques are electrogravimetry, potentiometry (including potentiometric titrations), conductometry, voltammetry/polarography, coulometry and electrochemical detection. Some electroanalytical techniques have become very widely accepted others, such as polarography/voltammetry, less so. Table 8.74 compares the main electroanalytical methods. 

Here the most important techniques are voltammetry, electrogravimetry and coulometry. 

Electrogravimetry is one of the oldest electroanalytical methods and generally consists in the selective cathodic deposition of the analyte metal on an electrode (usually platinum), followed by weighing. Although preferably high, the current efficiency does not need to be 100%, provided that the electrodeposition is complete, i.e., exhaustive electrolysis of the metal of interest this contrasts with coulometry, which in addition to exhaustive electrolysis requires 100% current efficiency. 

A Methods that electrolyze the electroactive species under study completely Electrogravimetry Coulometry... 

Electrogravimetry and Coulometry - Methods that Completely Electrolyze Electroactive Species 1143... 

A method that completely electrolyzes the substances under study is used in electrogravimetry and coulometry. The method is also useful in electrolytic separations and electrolytic syntheses. Electrolysis is carried out either at a controlled potential or at a controlled current. 

In the electrogravimetry and coulometry described in Section 5.6, the substance under study is completely electrolyzed in obtaining the analytical information. A complete electrolysis is also carried out in electrolytic syntheses and separations. Electrolytic methods are advantageous in that they need no chemical reagent and in that optimum reaction conditions can easily be obtained by controlling electrode potentials. 

Coulometry comes in several flavors constant-potential or potentiostatic coulometry, constant-current or amperostatic coulometry, coulometric titrations, and electrogravimetry. 

Coulogravimetry — A combination of -> coulometry and -> electrogravimetry, in which the weight of the deposited analyte and the passed charge are measured [i]. 

Electrogravimetry and coulometry are moderately. sensitive and among the most accurate and precise techniques available to the chemist. Like the gravimetric techniques discussed in Chapter 12, electmgravimetiy requires no preliminary calibration against chemical standards becau.se the functional relationship between... 

Electrogravimetry and coulometry can often exhibit accuracies of a few parts per thousand. 

Let us now examine these two phenomena in detail. As an example, consider the following electrolytic cell for the determination of cadmium(II) in hydrochloric acid solutions by electrogravimetry or coulometry ... 

The following cell has been used for the determination of cadmium in the presence of chloride ions by both electrogravimetry and coulometry. 

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