Competitive adsorption of anions in the electron transfer reaction between thiosulphate ion and methylene blue in acidic medium

摘要

Thiosulphate ion (TS) and methylene blue (MB) react in acidic medium in the presence of ethanol (5% v/v) and the reaction order in MB changes from zero to -1/2 at higher [TS] (ca. >8.0 X 10~(-4) mol dm~(-3)). The deviation in kinetic features has been attributed to the competitive adsorption of half-reduced MB radical (HM) and TS on colloidal sulphur, produced due to autodecomposition of thiosulphate ion. The addition of anions such as oxalate and phosphates retards the rate but these anions are found to exert deviating influences. The kinetics suggests that the adsorption of HM radical on colloidal sulphur is considerably influenced by the basicity of the anions.