Page:Text-book of Electrochemistry.djvu/178

 X.

��LAW OF DILUTION.

��rO.

��the fonnula -£" x Cab = C'a x Cb = ^ can be transformed

V

into —

��1-'''

��

��V

��= ^a or

��K=-^

�� ��(1 - zy

��The relationship expressed iu this formula is known as Ostwald's law, or the law of dilution (8).

The constant JT is termed the electrolytic dissociation constant of acetic acid.

��AcKTic Acid at 141^

��f.

�/ip.

�lOOa (obserred).

�lOOa (cttlcuUted)

�5-2(J

�5-«a

�46-

�20-;-)

�31<i

�HKI

��log K = 5-25 - 10(5-25). K = 00000178.

As is evident from the numbers given, the calculated and observed degrees of dissociation agree extremely well. In no other field in which the law of mass action has been appUed have so good results been, obtained.

This agreement between theory and practice, however, is only found for weak electrolytes, of which Ostwald investi- gated the acids and Bredig the bases (9),

It is just possible that even in this case the law of mass action is not undisturbed by other factors. The deviation from the law seems to be greater the stronger the acid is. Amongst the stronger organic acids deviations occur, e,g, with formic acid, and to an even greater extent with the

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