Tri-Bromide Equilihria. 



117 



Table XIII. 

 Cadmium Potassium Bromide. CdBr2.2KBr. 



1. a = 



0-1371 molar CdBi 



2.2KBr. 



2. a 



- 0-0686 molar CdBr 



2.2KBr. 



(2Br)-^ 



(2Br3)- 



4a = 0-548 molar. 



(2Br) + 



(2Br3) = 4a 



= 0-2745 



molar. 



h 



g 



c 



K^ 



h 



g 



c 



K, 



73-1 



413-0 



28-8 



0-119 



82-4 



763 



29-7 



0-099 



42-2 



226-6 



28-1 



0-121 



35-42 



282-1 



28-5 



0-097 



23-52 



122-7 



27-5 



0-124 



17-62 



135-4 



27-8 



0-100 



13-67 



70-9 



27-0 



0-128 



9-23 



68-2 



27-0 



0-101 



8-03 



41-4 



27-0 

 mean 



0-128 



5-10 



37-34 



27-0 

 mean 



0-101 





0-124^ 



0-099, 









Table 



XIV. 









Mercuric Potassium Bromide 

 1. a = 0-125 molar HgBr2.2KBr. 

 ( 2Br) + (SBrs) = 4a = O'S molar. 



b 

 46-8 

 26-94 

 20-07 

 12:23 

 7-42 



9 



686 

 378-3 

 273-3 

 161-1 



97-1 



c 

 29-5 

 28-6 

 28-4 

 27-8 

 27-0 

 mean 



0-470 

 0-469 

 0-451 

 0-444 

 0-467 

 0-460„ 



HgBr2.2KBr. 

 2. a = 0-05 molar HgBr2.2KBr. 

 (2Br) + (2Br3) = 4a = 0'2 molar. 



b 



32-53 



14-89 



9-90 



6-09 



3-941 



9 



613 

 263-5 

 190-8 

 104-4 



67-9 



c 

 29-6 

 28-3 

 28-0 

 27-4 

 27-0 

 mean 0-353, 



^1 

 0-330 

 0-324 

 0-434 

 0-330 

 0-350 



It is very noticeable that the only halides which give abnor- 

 mal results are those of cadmium and of mercury, salts which 

 are conspicuous for abnormal behavior in many other ways. 

 All other iodides and bromides^ so far as yet tested^ give in 

 dilute solution normal values of K^. 



Before taking up the discussion of the abnormal cases we 

 must examine a little more closely the nature and meaning of 

 the results in the normal ones. It is evident that the equili- 

 brium in normal cases is practically independent of the nature 

 and the valence of the positive ion. This indicates that the 

 equilibrium is primarily an ionic one, which, for an iodide, can 

 be written 



.ami (V) 



K. 



Comparison with the expression for our equilibrium constant 



( i)(y 



K. = 



(SI,) 



(IV) 



shows that K =•- K^—^ where 7 and 7^ are the degrees of ioniza- 

 tion of the iodide and tri-iodide, respectively, in the equilibrium 

 mixture. Assuming the constancy of ^, i.e. the validity of 

 Equation Y, the observed constancy of K^ requires that the 



