Bromine standard electrode potential

It should be remembered that the standard potential refers to the condition in which all the substances in the cell are in their standard states of unit activity. Gases such as hydrogen, oxygen and chlorine are thus at 1 atm. pressure. With bromine and iodine, however, the standard states are chosen as the pure liquid and solid, respectively the solutions are therefore saturated with these elements in the standard electrodes. For all ions the standard state of unit activity is taken as the hypothetical ideal solution of unit molality or, in other words, a solution for which the product my is unity, where m is the molality of the ion and y its activity coefficient. 

The standard open circuit potential of bromine/polysulphide RFBs reaches 1.515 V, but in practical applications, it depends on many factors, including electrode material, electrolyte composition, operating temperature, and state of charge. 

The number of unsaturated bonds can be determined by a titration with a standard solution of bromine dissolved in glacial acetic acid. The sample is also dissolved in glacial acetic acid to which sodium and ammonium acetate are added, so as to give a final concentration of 0-5 and OT M respectively. The cathodic current of bromine is measured with a short circuit system using a rotating platinum indicator, and a calomel or chloranil reference electrode at the potential of the reference electrode. Several unsaturated open chain compounds and terpenes have been titrated in this way.( ) Other modifications of this technique have been used to determine the amount of unsaturation in fats in methanolic solutions. The standard solution of bromine is prepared in methanol, saturated with sodium bromide, and the methylester of stearic acid is added to suppress the maxima. If the methanolic solution is acidified, OT M potassium bromate with OT M sodium bromide can be used instead of bromine. The bromine generated in homogeneous solution can be used to analyse xylenol and cresol fractions of coal-tars. Other phenolic compounds may be similarly determined. The method was used for the determination of small concentrations of styrene... 

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