Question

ions:
How did you find the activity?​

Answer 1

Answer:

Measurement of the Single Ion Activity

Whether the single ion activity (SIA) in a solution a can be in principle determined thermodynamically, remains debatable. It was Lewis who in 1907 first considered the concept of activity for ions in a solution, originally stating that “from the nature of the ions we are never able to determine the numerical values of their activities”.28 He originally applied this concept to the equilibrium constants of chemical reactions involving ions, in particular solubility of salts and dissociation of strong electrolytes, but also noted that “the application of equations … to the electromotive force of concentration cells (cell built by two half-cells containing the same redox couple with different concentrations of one component, typically of electrolyte in a solution) [is] a remarkably useful means of determining, in the case of imperfect solutions, how the activity of a given molecular species varies with the concentration”.28 Using the concept of ion activity proposed by Lewis, Bray in 1911 analyzed the solubility of uni-univalent salts (i.e., 1,1-electrolytes with z+ = |z−| = 1) in the presence of other salts.29 In 1912, Lewis analyzed change of activity coefficients using data on conductivity of solutions, solubility of salts, and the freezing-point depression in electrolyte solutions.30 Both Bray (“if it is legitimate to distribute this effect equally upon the two ions”) and Lewis (“introducing the assumption that both ions behave alike”) were forced to operate, in modern terms, with mean activity coefficients.