Indicators, redox

Redox doping Red oxide Redox indicators Redox polymers REDOX process Redox reactions Red PDC [80-22-8]... 

FIGURE 21.2 Experimental apparatus used to measure the standard reduction potential of the indicated redox couples (a) the acetaldehyde/ethanol couple, (b) the fumarate/succi-nate couple, (c) the Fe /Fe" couple. 

An oxidation-reduction indicator (redox indicator) is a compound which exhibits different colours in the oxidised and reduced forms ... 

C. Potentiometric methods. This is a procedure which depends upon measurement of the e.m.f. between a reference electrode and an indicator (redox) electrode at suitable intervals during the titration, i.e. a potentiometric titration is carried out. The procedure is discussed fully in Chapter 15 let it suffice at this stage to point out that the procedure is applicable not only to those cases where suitable indicators are available, but also to those cases, e.g. coloured or very dilute solutions, where the indicator method is inapplicable, or of limited accuracy. 

The typical amber color of the hexavalent chromium solution will turn to a pale green once the chromium has been reduced to the trivalent state. Although this color change is a good indicator, redox control is usually employed. 

Redox cycling of iron in salt marsh sediments. The solid lines and the dashed lines indicate redox reactions and precipitation reactions, respectively. 

Fig. 9 Energy level diagram indicating redox control of Os(II) complex luminescence [51]...

The general half-reaction applicable to an indicator redox couple is... 

Fig. 5. EPR spectra associated with the reduced intermediary acceptor i [BO"] formed in the reaction-center/cytochrome compiex and measured at different temperatures and microwave-power levels (A, B and C). (D) Redox titration of the I signal. Samples poised at indicated redox potentials and then illuminated for 3 m before being cooled to 7 K and assayed. See text for details. Figure source Tiede, Prince and Dutton (1976) EPR and optical spectroscopic properties of the electron carrier intermediate between the reaction center bacteriochlorophylls and the primary acceptor in Chromatium vinosum. Biochim Biophys Acta. 449 455, 460.

Summary and Comment on Eh versus /02 as Parameters to Indicate Redox... 

FIGURE 20.3 Expenmental apparatus used to measure the standard reduction potential of the indicated redox couples (a) the ethanol/acetaldehyde couple, (b) the fumarate/ succinate couple. Part (a) shows a sample/reference half-cell pair for measurement of the standard reduction potential of the ethanol/acetaldehyde couple. Because electrons flow toward the reference half-cell and away from the sample half-cell, the standard reduction potential is negative, specifically -0.197 V. In contrast, the fumarate/succinate couple (b) accepts electrons from the reference half-cell that is, reduction occurs spontaneously in the system, and the reduction potential is thus positive. For each halfcell, a half-cell reaction describes the reaction taking place. For the fumarate/succinate half-cell coupled to a H /H2 reference half-cell (b), the reaction taking place is indeed the reduction of fumarate. 

Reagent-less detection technique A procedure that uses no additional chemical reagents (indicator, redox mediator, enzyme substrate) to generate an anal3rtical signal of the DNA biosensor. 

See also Activation Anaiysis Neutron Activation. Atomic Emission Spectrometry Principies and Instrumentation. Bleaches and Sterilants. Chiroptical Analysis. Chromatography Principles. Conductimetry and Oscillometry. Coulometry. Fire Assay. Food and Nutritional Analysis Overview. Gas Chromatography Principles. Gravimetry. Indicators Redox. Infrared Spectroscopy Overview. Ion Exchange Oven/iew. Isotope Dilution Analysis. Lipids Fatty Acids. Liquid Chromatography Size-Exclusion. Radiochemical... 

In this article, the physicochemical principles of redox reactions are outlined as a preliminary to an account of the function of redox indicators. Redox indicators are sensitive to the pH of a solution as well as to its redox potential, and the nature of this dependence is described. There then follows a discussion of the various types of redox indicators used, and Table 1 gives details of a range of these indicators. 

Oxidation-Redaction Indicators.—Redox Indicators.— Many dyestuffs and natural pigments are converted to colourless leuco compounds on reduction. The change is reversible, and the colour intensity of the compound is determined by proportions of the components present. 

Used as a O.lmM soln. in EtOH as an acid-base indicator redox indicator for titanometric detn. of Fe(//7),... 

Na salt Used as acid-base indicator redox indicator. Used as 0.02% aq. soln. Red cryst. Sol. H2O. 6.1. E° -bO.563 V. 

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