454 SMITH'S INTERMEDIATE CHEMISTRY 



When, however, sodium acetate is dissolved in the liquid until the 

 solution is normal in respect to this substance also, which is 0.528 

 ionized in normal solution, the following additional equilibrium 

 has to be considered: 



(0.472) NaC 2 H 3 O 2 <=Na+ (0.528) + C 2 H 3 2 - (0.528). 



The concentration of acetate-ion from this source is 0.528, so that, 

 in the mixture of acid and salt, the concentration of acetate -ion 

 [C 2 H 3 O 2 -] will be 0.528 + 0.004 = 0.532, or 133 times larger 

 than in the acid alone. Hence, in order that the ionization con- 

 stant K may recover, as it must, its original value, [H+] must 

 be diminished to something like T ^ of its former magnitude. 

 That is, [H+] will become equal to about 0.00003, 



0.00003 X 0.532 



the rest of the hydrogen-ion uniting with a corresponding amount 

 of the acetate-ion to form molecular acetic acid. The concen- 

 tration of this increases only from 0.996 to 0.99997; in other words, 

 so much is already present that its concentration is practically 

 unchanged. The chief effect of adding this amount of sodium 

 acetate therefore is, as we have seen, to reduce the concentration 

 of the hydrogen-ion below the amount which can be detected by 

 use of an indicator like methyl-orange. 



This effect is of course reciprocal, and the ionization of the 

 sodium acetate will be reduced also. But the acetate-ion fur- 

 nished by the acetic acid is relatively so small in amount that the 

 effect it produces on the ionization of the salt is imperceptible. 



Although, therefore, acetate-ion and hydrogen-ion must dis- 

 appear in equivalent quantities, for they unite, there is, however, so 

 much of the former that the loss it sustains goes unremarked, while 

 there is so little of the latter that almost none of it remains. 

 When substances of more nearly equal degrees of ionization are 



