Specific Ionic Effects on Reaction Rates. The Reaction between Persulfate and Iodide Ions in the Presence of High Concentrations of Added Salts

The effect of added electrolytes (up to 2M) on the reaction between persulfate and iodide ions was reinvestigated, utilizing the absorption of I₃^— in the near ultraviolet to follow the reaction. The effect could be represented very well by the empirical relation $$\log \mathrm{k=}\log k_0\mathrm{+[Ac/(B+c)]+Dc}$$ over the entire range, where A, B, and D are constants specific for the cation (uni‐, di‐, or trivalent) employed, and k₀ and k are the rate constants in the absence and in the presence of added electrolyte at concentration c. The inapplicability of the concept of ionic strength to the reaction between two anions is discussed and contrasted with the behavior of reactions between ions of unlike sign.