The thermodynamics and kinetics of the reaction between Ni2+(aq) and the metal ion indicator murexide (Mu-) have been studied over the pH range 4.0-7.3 in aqueous solution. Rates and equilibrium concentrations are strongly pH-dependent. Rate constants were obtained using pressurejump and stopped-flow methods and results from both techniques are in excellent agreement. All data are consistent with the reaction scheme : ki KH Ni2++ Mu-e (NiMu)+ + (NiMu)d, + H+. k-1 slow fast The reaction (involving charged reagents) is studied in the absence of added inert electrolyte and, therefore, under conditions of varying ionic strength. A general treatment for handling rate and equilibrium data in this situation is described. By the inclusion of appropriate activity coefficients the following results (at 298.2 K) are obtained : Kl = kl/k-l = 3.8(+0.2) x lo3 dm3 mo1-1 ; kl = 7.8(f0.5) x lo3 dm3 mo1-1 s-1 ; KH = 1.8(+0.2) x 1P6 mol dm-3 k-l = 2.1 s-I.Such indicator reactions involving murexide are very convenient for the study of various aspects of micellisation and their application to the detection of micelles formed by anionic detergents is described.
Presents a series of experiments in flash kinetic spectrophotometry that train the student in fast reaction methodology and the physical principles of photochemistry.
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