NOVEMBER. 1949
ELECTROMOTIVE FORCE OF CELLS WITH TRANSFERENCE T. 1. PHILLIPS Evansville College, Evansville, Indiana
IN
MOST elementary physical chemistry textbooks the formulas for calculating the junction potential and the total potential of cells with transference are either given without proof or the student is referred to a text on electrochemistry. Since these texts are presented from a more mature viewpoint, the student is often more confused than before. By use of a simple device I have found i t possible for the student not only to develop these formulas easily when required hut I believe his understanding of the physical process represented is deepened. As an example the cell
The respective potentials Ej,.,,,, and Etoblare then obtained from the formulas with which the student is familiar. From (4)
but where m is the molality and coefficient. Hence
r+ is the mean activity
Pt; Hz(~atm.),HCl(o=l)IHCl(a=z.), Hz(latm); Pt
has the cell reaction '/zHz(iatm.) H+o=z c H+,=z
+
= = =
+
H+n=l r 1/,Hz(1atm.) H+,,=I
(1)
Now using the convention that the left electrode is the oxidation electrode the ions migrate as follows, i. e., toward the electrode of the opposite charge. HC,=l-
H+o=2
(2)
of the more usual form which shorn the dependence of E, upon the transference numbers
The total electromotive force is even more easily obtained. ildding (1) and (4) and transposing we obtain
If one faraday of electricity is transported n+ n- = 1 we obtain faradays will be carried by the cation and n faradays remembering that n+ by the anion where n+ and n are the respective transference numbers. If the student understands that equations (2) and (3) signify quantities of electricity transported the equation for the transference of one utilizing (6) the formula is in the usual textbook form faraday is seen to be the sum of these two processes and (4) represents the junction reaction.
+
By using the device in (4) the student can readily develop formulas for junction and total potentials of cells with transference.
