SOLUTIONS AS A FUNCTION OF TEMPERATURE 149 



H 2 S0 4 = H+ + HS0 4 - 

 HS0 4 - = H + + S0 4 - 



At the higher concentrations, the second ionization process has taken 

 place to only a small extent and the form of the curve is largely due to 

 the change in the ionization according to the first process, the maximum 

 point occurring when the increased conductance of the ions due to tem- 

 perature is just counterbalanced by the decreased conductance due to 

 decrease in ionization. At the lower concentration the second ionization 

 process is likewise involved. The second ionization corresponds to that 

 of the weaker acid and the ionization according to this process falls off 

 more rapidly with rising temperature, thus giving rise to the initial 

 maximum. When the ionization according to the second process has 

 been largely depressed, the curve thereafter depends chiefly upon the 

 ionization according to the first equation. 



The ionization of strong electrolytes, apparently without exception, 

 decreases with increasing temperatures; but at lower temperatures the 

 rate of decrease is relatively small. In the case of the weak acids and 

 bases the ionization increases between and 40, and thereafter de- 

 creases rapidly at higher temperatures. In the following table are given 

 values for the ionization constants of ammonium hydroxide and acetic 

 acid. 8 The values represent averages for a number of concentrations. 

 In general, the ionization constant is independent of concentration up 

 to 0.1 normal. 



TABLE LII. 



IONIZATION CONSTANT X 10~ 8 FOB AMMONIUM HYDROXIDE AND 



ACETIC ACID. 



18 25 218 306 



NH 4 OH 17.2 18.1 1.80 0.093 



CH 3 COOH 18.3 1.72 0.139 



Initially there is a slight increase in the ionization constant, after 

 which there is a sharp decrease at higher temperatures. Between 218 

 and 306 the constant of ammonium hydroxide changes slightly more 

 than that of acetic acid. Similar results have been obtained in the case 

 of other weak acids. For example, the ionization constant of diketo- 

 tetrahydrothiazole 9 at 0, 18 and 25 is respectively 0.0711 X 10' 6 , 

 0.146 X 10- 6 and 0.181 X 10~ 6 . Between and 25 the constant of am- 

 monium hydroxide varies between 13.91 and 18.06 X 10~ 6 . It appears 



Noyes, Joe. tit., p. 234. 



/bid., Joe. cit., p. 290. 



