HOMOGENEOUS IONIC EQUILIBRIA 227 



These equations are independent of the concentration of the various 

 reacting constituents so long as the assumed conditions are fulfilled. In 

 many instances they may be greatly simplified for practical purposes. 

 If the concentration of the salt is not extremely low and if the acid is 

 stronger than the base, the concentration of the hydroxyl ions may be 



neglected in comparison with that of the M + ions, and the term - -r 



K b h 



may be dropped out of the equations. If the hydrolysis is small, the 

 concentration of the hydrogen ions may be neglected in comparison with 

 that of the M + ions. The equation, then, reduces to the form: 



K w 



v v r* ft i,\2 i v n /t it\ 



K a K b L b ( l ~ h ) K b t b (lh) 



If acid and base are present in equivalent amounts, the hydrolysis of the 

 salt is expressed by the equation: 



(!-*) K a K b ' K b C b (l-h) 

 and the hydrogen ion concentration by: 



(61) 



K w K a K w y 8 C b d-K) 



These equations are generally applicable, provided the concentration of 

 the hydrogen ions is relatively small in comparison with that of the ions 

 of the salt. In the case of a solution of a strong acid and a weak base, 

 the second term in Equation 60 is evidently determinative of the degree 

 of hydrolysis of the salt, while in solutions in which both the acid and 

 base are very weak and the total concentration of the base is high, the 

 first term is chiefly determinative of the hydrolysis. In the case of acids 

 and bases of intermediate strength, and particularly at fairly low con- 

 centrations, both terms must be taken into account in determining the 

 hydrolysis of a salt. 



In very dilute solutions of salts of relatively strong acids and bases, 

 it is possible that conductance measurements may be appreciably affected 

 by hydrolysis. This is particularly true if the limiting values of the 

 ionization constant approached by acid and base differ. It is obvious 

 that the actual concentration of acid and of base in solution is very low, 



