Oxidation-reduction equivalent mass

What fraction of the formula mass is the oxidation equivalent mass or reduction equivalent mass of each of the oxidizing or reducing agents in the equations of Exercise 11-7 ... 

The equivalent is defined in terms of a chemical reaction. It is defined in one of two different ways, depending on whether an oxidation-reduction reaction or an acid-base reaction is under discussion. For an oxidation-reduction reaction, an equivalent is the quantity of a substance that will react with or yield 1 mol of electrons. For an acid-base reaction, an equivalent is the quantity of a substance that will react with or yield 1 mol of hydrogen ions or hydroxide ions. Note that the equivalent is defined in terms of a reaction, not merely in terms of a formula. Thus, the same mass of the same compound undergoing different reactions can correspond to different numbers of equivalents. The ability to determine the number of equivalents per mole is the key to calculations in this chapter. 

Equivalent masses are so defined because equal numbers of equivalents of two substances react exactly with each other. This is true for neutralization because one H+ neutralizes one OH-, and for oxidation-reduction reaction because the number of electrons lost by the reducing agent equals the number gained by the oxidation agent (electrons cannot be eliminated—by the law of conservation of matter). 

These laws (determined by Michael Faraday over a half century before the discovery of the electron) can now be shown to be simple consequences of the electrical nature of matter. In any electrolysis, an oxidation must occur at the anode to supply the electrons that leave this electrode. Also, a reduction must occur at the cathode removing electrons coming into the system from an outside source (battery or other DC source). By the principle of continuity of current, electrons must be discharged at the cathode at exactly the same rate at which they are supplied to the anode. By definition of the equivalent mass for oxidation-reduction reactions, the number of equivalents of electrode reaction must be proportional to the amount of charge transported into or out of the electrolytic cell. Further, the number of equivalents is equal to the number of moles of electrons transported in the circuit. The Faraday constant (F) is equal to the charge of one mole of electrons, as shown in this equation ... 

Equivalent mass based on oxidation-reduction reactions. For oxidation-reduction reactions, the equivalent mass is defined as the mass of substance per mole of electrons involved (Snoeyink and Jenkins, 1980). 

The previous reactions are oxidation-reduction reactions, so it is appropriate to use as the reference species the number of electron moles involved, although the choice of the reference species is completely arbitrary. One atom of Fe is being oxidized to Fe, therefore, one electron mole is involved (thus, the number of reference species = 1) and the equivalent masses are ferrous = Fe/1 = 55.8, chlorine = CI2/I = 35.5, potassium permanganate = i KMnOVl = 52.67, ozone = i O3/I = 8.0, and oxygen 03/ = 8.0. 

Titrations are widely used in analytical chemistry to determine acids, bases, oxidants, reductants, metal ions, proteins, and many other species. Titrations are based on a reaction between the analyte and a standard reagent known as the titrant. The reaction is of known and reproducible stoichiometry. The volume, or the mass, of the titrant needed to react essentially completely with the analyte is determined and used to obtain the quantity of analyte. A volume-based titration is shown in this figure, in which the standard solution is added from a buret, and the reaction occurs in the Erlenmeyer flask. In some titrations, known as coulometric titrations, the quantity of charge needed to completely consume the analyte is obtained. In any titration, the point of chemical equivalence, experimentally called the end point, is signaled by an indicator color change or a change in an instrumental response. 

Equivalent Weights in Oxidation/Reduction Reactions The equivalent weight of a participant in an oxidation/reduction reaction is that amount that directly or indirectly produces or consumes 1 mol of electrons. The numerical value for the equivalent weight is conveniently established by dividing the molar mass of the substance of interest by the change in oxidation number associated with its reaction. As an example, consider the oxidation of oxalate ion by permanganate ion ... 

Special information about the electrode reactions is often needed in order to calculate the equivalent mass for electrolysis, just as in ordinary oxidation-reduction reactions. If a solution containing Fe " is electrolyzed at low voltages, the electrode reaction for the iron might be... 

The active form of lactate dehydrogenase (mass 144 kDa) is a tetramer consisting of four subunits (1). Each monomer is formed by a peptide chain of 334 amino acids (36 kDa). In the tetramer, the subunits occupy equivalent positions (1) each monomer has an active center. Depending on metabolic conditions, LDH catalyzes NADH-de-pendent reduction of pyruvate to lactate, or NAD -dependent oxidation of lactate to pyruvate (see p. 18). 

The rotating disc electrode is constructed from a solid material, usually glassy carbon, platinum or gold. It is rotated at constant speed to maintain the hydrodynamic characteristics of the electrode-solution interface. The counter electrode and reference electrode are both stationary. A slow linear potential sweep is applied and the current response registered. Both oxidation and reduction processes can be examined. The curve of current response versus electrode potential is equivalent to a polarographic wave. The plateau current is proportional to substrate concentration and also depends on the rotation speed, which governs the substrate mass transport coefficient. The current-voltage response for a reversible process follows Equation 1.17. For an irreversible process this follows Equation 1.18 where the mass transfer coefficient is proportional to the square root of the disc rotation speed. 

These carboxylate ions are weaker counterions than CP and Pp, so that the corresponding dendrimers tend to ionize more easily and to give clearer signals in MALDI-TOF mass spectra. As to the electrochemical properties, their cyclic voltammetries show a reversible metal centered oxidation and two reversible ligand-centered reduction processes at potential values very similar to those of the corresponding dendrimers with CP counterions. Therefore, the [Ru(tpy)2]2+ complexes are electrochemically equivalent and can efficiently store charges. 

Support an hemispherical iron dish of 10 cm. diameter (or an iron crucible) on a ring stand and place in it about 75 g. of sodium nitrate. Heat the nitrate until it melts and just begins to evolve bubbles of oxygen. While maintaining a steady temperature, drop in pieces of granulated lead or chopped-up lead pipe, stirring well with an iron rod (old round file) after each addition. A little more than the equivalent of lead should be added, since some of it will be oxidized by the air. For this reason, a flat iron sand-bath dish is not suitable for the experiment. The reduction of the nitrate is rapid, and if much lead is added at a time, the mass may become incandescent. 

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