Bromine/bromide electrode

Halogen electrodes in molten salts are being used especially for the study of molten halides. In 1930 Hildebrand and Salstrom [98-100] were the first who applied a chlorine reference electrode in molten salts. Up to the present, other authors used and improved this electrode [101-105], The reversible bromine/ bromide electrode was set up for the first time by Hildebrand and Salstrom [98] and improved by Murgulescu et al. [106,107], In the following an example is shown of how to obtain and use a reversible gas electrode in molten salts for the determination of thermodynamic activity. 

As a positive active material for rechargeable cells, bromine offers various attractive properties such as high voltage and specific energy and power. The main difficulty encountered with the operation of a battery using bromine/bromide electrode is the necessity to develop a suitable for the storage of this aggressive and toxic elemental... 

SAQ 7.11 Write down an expression for the electrode potential of the bromine bromide couple. [Hint it might help to write the balanced redox reaction first.]... 

Appendix 2), so the bromine-bromide couple is fully reversible, and therefore the two peaks - anodic and cathodic - are positioned at an equal distance either side of 1.09 V (see Table 6.3). The forward peak represents the electrode reaction, 2Br -> Br2 + 2e , while the reverse peak represents the reverse electrode reaction, Br2-f-2e" 2Br. We recall that the CV peak height is... 

EXAMPLE 15-1 Consider the titration of arsenic(III) with bromate. In a hydrochloric add solution containing excess bromide, the end point can be determined potentiometrically by using the bromine-bromide couple as the potential-determining system. Alternatively, the same titration can be followed amperometrically by measuring the diffusion-controlled current due to excess bromine slightly beyond the end point. At an initial concentration of 5 x 10 M arsenic(III), the potentiometric titration can barely be carried out, because several minutes are required for electrode equilibrium at each point of the titration. The amperometric method gives a successM end point even at 5 x 10 M arsenic(III), the whole titration taking only a few minutes. ////... 

The mechanisms and kinetics of reactions at the bromine-side electrode are generally agreed to be more complicated than those at the zinc-side electrode. This complexify is primarily attributed to the presence and interactions of multiple versions of bromide species (Br , Bri, Brs, etc.) in the electrolyte solution, as well as the electrochemical and possibly surfactant-like effects of the particular BSA used. The structures and bonding present in polybromides have been studied using periodic density functional theory and found to have closed-shell interactions between the Br anion and multiple Br2 species [16]. A recent smdy has shown that high-order bromide anions can exist in ionic hquid systems, including a polymeric [17]. 

The reactions at GC electrodes, however, contain one slow step reaction in each of the two common reaction pathways for bromine-bromide redox [12], as shown by Eqs. 5.5-5.10 ... 

Fabjan C, Hirss G (1986) On the kinetics and mechanism of bromine/bromide redox electrodes. Dechema Monogr 102 149-161... 

When M is a voltmeter an indication of the energy difference between the reactants and products is obtained (see below). A current passes when M is an ammeter, and if a little potassium thiocyanate is added to the Fe (aq) a red colour is produced around the electrode, indicating the formation of iron(III) ions in solution the typical bromine colour is slowly discharged as it is converted to colourless bromide Br . 

Bromine has a lower electron affinity and electrode potential than chlorine but is still a very reactive element. It combines violently with alkali metals and reacts spontaneously with phosphorus, arsenic and antimony. When heated it reacts with many other elements, including gold, but it does not attack platinum, and silver forms a protective film of silver bromide. Because of the strong oxidising properties, bromine, like fluorine and chlorine, tends to form compounds with the electropositive element in a high oxidation state. 

Chlorine has a lower electrode potential and electronegativity than fluorine but will displace bromine and iodine from aqueous solutions of bromide and iodide ions respectively ... 

In the dectrolysis of aqueous cupric bromide, CuBr2, 0.500 gram of copper is deposited at one dectrode. How many grams of bromine are formed at the other electrode Write the anode and cathode half-reactions. 

When 1-methyl-, 1,2- and 1,3-dimethyl-indoles were oxidized on a platinum electrode in methanolic ammonium bromide solution, in addition to the oxidation products, products of nuclear bromination at the 3-and 5-positions were observed. 1,2- Dimethylindole (20) gave 3-bromo-1,2-dimethylindole (81CCC3278) [bromine in chloroform gave the same product (85CHE786)]. In acidic conditions the amidinium cation formed from 20 was brominated in the 5-position (Scheme 14). Acylated 2-aminoindoles reacted similarly in neutral media to give 3-bromo derivatives and when protonated to give 5-bromo products. Bromine in chloroform transformed l-methyl-2-dimethylaminoindole (21) into the 3-bromo derivative (85CHE782) (Scheme 15). 

G. N. Lewis and H. Storch, "The Potential of the Bromine Electrode the Free Energy of Dilution of Hydrogen Bromide the Distribution of Bromine Between Several Phases". J. Am. Chem. Soc., 39, 2544-2554 (1917). 

Kubiak CP, Schneemeyer LF, Wrighton MS (1980) Visible fight driven generation of chlorine and bromine. Photooxidation of chloride and bromide in aqueous solution at illuminated n-type semiconducting molybdenum diselenide and molybdenum disulfide electrodes. J Am Chem Soc 102 6898-6900... 

Other methods for the determination of chlorine in seawater or saline waters are based on the use of barbituric acid [13] and on the use of residual chlorine electrodes [ 14] or amperometric membrane probes [15,16]. In the barbituric acid method [12], chlorine reacts rapidly in the presence of bromide and has completely disappeared after 1 minute. This result, which was verified in the range pH 7.5-9.4, proves the absence of free chlorine in seawater. A study of the colorimetric deterioration of free halogens by the diethylparaphenylene-diamine technique shows that the titration curve of the compound obtained is more like the bromine curve than that of chlorine. The author suggests... 

Wunsche An electrolytic process for liberating bromine from a bromide solution. It uses carbon electrodes and a porous clay separator. Developed in Germany in 1902. See also Kossuth. 

For convenience, we will discuss here the formation of charges with the example of copper metal immersed in a solution of copper sulphate (comprising Cu2+ ions). We consider first the situation when the positive pole of a cell is, say, bromine in contact with bromide ions, causing the copper to be the negative electrode. 

When the scan rate is fast - say 500 mV s - the CV is obtained very quickly, so any bromine generated at the electrode will have too little time to react to any significant extent before it is electro-reduced back to bromide. The ratio, /pc//pa, will be close to unity at this scan rate. 

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