274 



Conductivity of Aqueous Solutions. Part VIII. 

 Table 118. The ionisation-relations of sulphuric acid. 



These values probably arise from experimental error. 



We may next consider the ionization-relations of the potassium hydro- 

 gen sulphate. It follows from the principle that the primary ionization 

 of the sulphuric acid is the same as that of hydrochloric acid that the 

 concentration of the un-ionized sulphuric acid is always so small in the 

 solutions of the potassium hydrogen sulphate that the calculation of the 

 hydrogen-ion concentration made under the assumption that the former 

 concentration (or y 3 ) is zero is substantially correct, and therefore that the 

 second or larger numbers given in table 117 are more nearly the true 

 values for the hydrogen-ion concentration. In order to get fairly accurate 

 values for the sulphate-ion and hydrosulphate-ion concentrations in solu- 

 tions of the salt, it is, however, desirable to form an estimate of the concen- 

 tration of the un-ionized sulphuric acid (H 2 S0 4 ) and the un-ionized potas- 

 sium sulphate (K 2 S0 4 ). As the latter was entirely disregarded in the 

 previous calculation, a more accurate value of the hydrogen-ion concentra- 

 tion will also be thereby obtained. 



In deriving these final values we have proceeded as follows. We make 

 the preliminary assumption that Cso 4 = Cn (taking for Cn/C the larger 

 of the two values given in table 117), and that Chso 4 = Cy Cso 4 . 

 Applying then the mass-action principle* that in a mixture of two sub- 

 stances with a common ion the un-ionized fraction of each is the same as 



*That this principle is also applicable to salts of these types, even though the 

 change of their ionization with the concentration does not conform to the mass- 

 action law, has been shown by Noyes (Z. phys. chem., 52, 634, 1905). 



