Specific cation effects on rate of reaction between persulphate and ferrocyanide ions

Abstract

The rate of the second-order reaction between persulphate and ferrocyanide ions can be accurately measured in dilute solution by spectrophotometric determination of the ferricyanide ions produced. The kinetic salt effect of added salts of various valency types has been investigated. The specific effects of added cations on the rate of reaction are large. Analysis of the results suggests that a cation is a necessary member of the activated complex, and a set of catalytic constants is reported. The significance of the results in relation to those for other reactions is discussed.We believe that at sufficiently low ionic concentrations the primary kinetic salt effect of added "inert" salts on the rate constant k of a reaction involving ions is correctly described by the equation obtained by substitution of the Debye-Huckel equation for ionic activity coefficients into the Brarnsted 1 equation, which for a second-order reaction between ions A and €3 isand f A , f~ and f A B are activity coefficients. Deviations from standard behaviour at higher ionic concentrations can sometimes be adequately accounted for 2 by extending the Debye-Hiickel equation to take account of specific interactions between oppositely charged ions. However, in other cases the specific effects are large and the existence of additional equilibria involving reactant ions, e.g., ion-pair formation, and/or additional rection pathways is postulated.3The rate of the second-order reaction between persulphate and iodide ions 4 is specifically affected by a variety of cations even at ionic strengths below 0.1 mole 1.-1, and there are also pronounced specific anion effects. Another reaction involving the persulphate ion which proceeds at a convenient rate for kinetic study is that with the ferrocyanide ion, and a comparison of the specific kinetic salt effects with those observed in the persulphate +iodide reaction is of interest. Previously 5 the kinetics of the persulphate-ferrocyanide reaction had been investigated by a volumetric method. At suitable time intervals excess potassium permanganate, which reacts rapidly with ferrocyanide, was added to samples ; the unreacted permanganate was then determined by back titration against standard ferrocyanide solution. For accurate measurements in dilute solution it is better to follow the reaction spectrophotometrically. The ferricyanide ion has an absorption peak at 4200 A, whereas the optical absorption of the ferrocyanide ion is negligible at this wavelength. Chlebek and Lister 6 have also used the spectrophotometric technique to study the effect of potassium ions on the same reaction. EXPERIMENTAL MATERIALS A N D S T O C K SOLUTIONSAnhydrous potassium ferrocyanide was prepared by heating once recrystallized A.R. trihydrate to constant weight at 100-1 10°C and cooling the product over anhydrous calcium chloride. The purity of the product was checked by titration against standard ceric sulphate.

Heterogeneous versus homogeneous electron transfer reactions at liquid–liquid interfaces: The wrong question?

“…One possible explanation might lie in the choice of the cation: the data obtained in this work and by Tatsumi and Katano utilized potassium salts, while Osakai et al used sodium ferro/ferricyanide. Indeed, the rate of reaction between for example persulfate and ferrocyanide depends strongly on both the type of the cation and the ionic strength [56].…”

Elaboration on the Electronics of Salen Manganese Nitrides: Investigations into Alkoxy-Substituted Ligand Scaffolds

“…It should be noted that the magnitude of the rate constant values collected at −78 °C for MnN­(Sal t Bu ) and MnN­(Sal CF 3 ) by the electrochemical method differ from previous measurements determined by decay of the ligand-to-metal charge-transfer (LMCT) bands in the UV–vis–near-IR (NIR) spectra at the same temperature . This difference observed in the electrochemically determined rate data can likely be attributed to the positive influence of an electrolyte on the rate constant of the bimolecular process involving like-charged species. − …”

Fused organic salts. 8. Properties of molten straight-chain isomers of tetra-n-pentylammonium salts

“…Equation 6 represents nonelectrostatic interaction of Q+A-with the surface, in which case increasing surface area should increase the van der Waals contacts of Q+ with the surface and increase retardation. The surface area of the ellipsoidal Q+ relative to that of quasi-spherical Q5,5,5,5+, A/Asph, is just the reciprocal of the shape factor &.…”

“…(6) Equations 3 and 4 represent association of Q+ with a polar site on the adsorbent. The former involves electrostatic interactions of the type shown in Figure 1 B, whose dependence on charge placement is shown in Figure 2A.…”