i 7 8 



Conductivity of Aqueous Solutions. Part VI. 



means of the cube-root equation, so as to enable a comparison of this 

 substance to be made with hydrochloric acid for which the results were 

 presented in Part V. 



It was shown in section 68 that the equivalent conductance A of sodium 

 hydroxide changes with the concentration C in accordance with the 

 expression C(A A) = K(CA)", where n is approximately 1.5, whence 

 it follows that the ionization y follows approximately the analogous law 

 C(l y) = K(Cy) 1 - 5 . Thus substantially the same relation between 

 ionization and concentration holds true for this base as for hydrochloric 

 acid and all the neutral salts thus far investigated. 



That to ammonium hydroxide the mass-action law is applicable even at 

 the higher temperatures is shown by the values of the ionization-constant 

 (Cy 2 )/(1 y) given in table 64. The concentration used in the calcula- 

 tion and given in the table is expressed in equivalents per liter and the 

 constants have been multiplied by 10 6 . 



Table 64. lonization-constants (X 10 6 ) for ammonium hydroxide. 



The agreement is seen to be excellent. The last row of values at the 

 highest concentration are the most reliable ones to adopt as final values of 

 the constant. 



The effect of temperature on the ionization-values will be seen from 

 table 63. Those of sodium hydroxide like those of all other largely 

 ionized substances investigated steadily decrease with rising temperature, 

 and by about the same amount as with hydrochloric acid, whose percent- 

 age ionization at 10 milli-normal is 97.1 at 18, 95.0 at 100, 93.6 at 156, 

 and 92.2 at 218. It is of some interest, too, to note, that ammonium ace- 

 tate though a salt of both a weak acid and a weak base has about the same 

 percentage ionization as sodium acetate, for which the values in 10 milli- 

 normal solution are 91.2 at 18, 88.8 at 100. and 88.0 at 156. 



The ionization of ammonium hydroxide (table 63), and of course also 

 its ionization-constant (table. 64), increases slightly between 18 and 51, 

 which is in accordance with the fact that its ionization at 18 is attended 

 with an absorption of heat of about 1,500 cal., since its heat of neutraliza- 

 tion with hydrochloric acid is 12,200 cal. Above 100, however, the ioni- 

 zation decreases rapidly, as with other substances. 



