272 



Conductivity of Aqueous Solutions. Part VIII. 



Table 117. Preliminary values of the percentage ratio (1007 : ) of hydrogen-ion 



concentration to total hydrogen concentration in solutions of 



potassium hydrogen sulphate. 



These preliminary values are given here, because they are essential to 

 the fuller discussion of the ionization-relations of sulphuric acid and its 

 acid salt. More accurate values of the hydrogen-ion concentration in solu- 

 tions of this salt are derived below and will be found in table 119. 



It is seen from these results that at 18 the potassium hydrogen sulphate 

 is in 0.002 molal solution almost completely dissociated into hydrogen-ion 

 and sulphate-ion ; but that in 0.1 molal solution this dissociation has taken 

 place only to an extent of 42 per cent, the rest of the salt existing to an 

 extent of 15 per cent as un-ionized KHS0 4 and to an extent of 43 per cent 

 either as HS0 4 " or as H 2 S0 4 + SO/. At 100 the hydrogen-ion concen- 

 tration has become very much less at all three concentrations, and at 156 

 in the 0.1 molal solution it is scarcely appreciable. This justifies the con- 

 clusion that sulphuric acid itself at 156 and above is at moderate dilutions 

 dissociated only into hydrogen-ion and hydrosulphate-ion ; for the disso- 

 ciation of the latter ion would of course be much less in the solution of the 

 acid than of its acid salt, owing to the presence in the former of the hydro- 

 gen-ion coming from the dissociation of the first equivalent of hydrogen. 

 Since under these conditions sulphuric acid dissociates as a monobasic 

 acid, it is of interest to compare its ionization with that of hydrochloric 

 acid at the same molal concentration, say at 0.04 molal. The ionization of 

 sulphuric acid may be obtained by doubling the second values given in 

 tables 114 and 115, that of hydrochloric acid by interpolation between the 

 values given for other concentrations in table 115 and in table 41, section 

 56, Part V. The ionization values for the 0.04 molal acids are as follows : 



This shows that the two acids have at these temperatures not far from 

 the same ionization-tendency (with reference in the case of sulphuric acid 

 to the primary dissociation, that is, that of the first equivalent of hydro- 



*This value is doubtless a little too high because of slight secondary ionization. 



