Dee.! 1962
NOTES
271 1
of NaF as a high temperature cryoscopic medium were discussed in a previous p ~ b l i c a t i o n . ~ For fixed alkaline earth fluoride concentration it was found4 that the smaller the alkaline earth cation radius the greater was the negative deviation from ideal solution behavior for KaF. In this particular investigation it was of interest to test whether this trend in solution behavior also applied to tetravalent fluorides. The tetravalent fluorides were chosen because their cations have electric field strengths that are considerably greater than those of any alkaline earth cation.
0
-0.05
-0.1
-0.15
E - A Q ( m v . vs. H.E. Fig. 1.-Corrected Tafel plot for the reduction of 5 mM MI08 a t 25" on mercury in 0.02 M MOH ( 0 en symbols) and 5 mM MIOa in 0.02 M MOH and 0.1 M ME1 (solid symbols; except for KCl, which was 0.4 AI); I in pa. cm.-2.
There is a shift toward lower values of IE - A01 with increasing concentration for R b + and especially for Cs+. This observation is in agreement with previous ~ o r kon~ the , ~ reduction of other anions and is accounted for by specific cation adsorption. The position of the two lines for Li+ in Fig. 1, however, is abnormal, since they correspond to lower values of / E - A91 than for Na+ and I
