CHAPTER XII.

Equilibrium between Several Electrolytes.

Isohydric Solutions. — In Chapter X. we have discussed the equilibrium between the ions and the undissociated part of an electrolyte ; but, of course, when several electrolytes are simultaneously present in the solution the relationships become somewhat more complicated.

Let us consider aqueous solutions of two acids which obey Ostwald's dilution law (see p. 162). Let there be a gram-ions of one acid, A, in volume Fj^, and /3 gram-ions of

the other acid, B, in volume V^. Then if - = ^-, no change

in the dissociation will occur when the two solutions are mixed. For if Kx is the dissociation constant of the first acid, then for the solution we have the following equation : —

��(-;.) = ^

��n " a

��A ' A

��where n is the number of gram-molecules of the acid (which is supposed to be monovalent). After mixing, the quantity a of the anion from acid A will be changed to ai, and the quantity /3 of the anion of acid B becomes /3i. The quantity of positive (H) ion from A becomes ai -J- /3i, and the volume is changed from F"^ to F^ + F^. Consequently, aft^r mixing, we have —

ai a\ + /3i j^ n ^ a\

( y. + >h) ( v,+ v,)~ * ( r, + vS

�� �