Section 79. Errors in the Solutions and their Correction. 207 



the case of the ammonium chloride and the sodium acetate solutions at 

 218 or 306 this correction is conveniently calculated in combination with 

 the correction for the hydrolysis of the salt, which is not entirely negligible 

 even in the presence of the excess of ammonium hydroxide or acetic acid 

 added. And in the case of the ammonium acetate solutions containing an 

 excess of ammonium hydroxide or acetic acid at 218 and 306, the water 

 correction is best combined with that for the conductance of the excess 

 of base or acid present. Thus in the solutions of ammonium chloride or 

 acetate containing an excess of the hydroxide, the concentration of un- 

 ionized ammonium hydroxide is approximately equal to the concentration 

 of the ammonium hydroxide added (Cb) plus that (Ch) arising from the 

 hydrolysis of the salt (the latter term Ch being negligible in the case of 

 the chloride) ; and that of the ammonium-ion is given approximately by 

 the ratio (multiplied by 10 3 ) of the specific conductance of the solution 

 (l), to the equivalent conductance A of the completely ionized salt. The 

 combination of the expressions of these two facts with the mass-action 

 equations for ammonium hydroxide and water gives the formulas : 



Con = 10~ 3 and Ch = 7; 



L CoH 



where the concentrations (both those given directly and those involved in 

 Kb and K-w) are expressed in equivalents per liter. In the ammonium 

 chloride solutions part of the hydrogen corresponds to the excess of 

 chloride-ion over ammonium-ion, the remainder to the hydroxide-ion in the 

 solution ; hence the correction to be subtracted from the specific con- 

 ductance is : 



10- 3 [Coh (Ah + Aoh) + (Ch Coh) (Ah + A c ,)] 



In the ammonium acetate solutions, on the other hand, part of the 

 hydroxide-ion corresponds to the excess of ammonium-ion over acetate- 

 ion, and the remainder to the hydrogen-ion in the solution ; hence the cor- 

 rection to be subtracted is : 



10- 3 [Ch (Ah + Aoh) + (Coh Ch) (A N h 4 + Aoh)] 



The calculations are in every way similar for sodium acetate and for 

 ammonium acetate with excess of acetic acid, Ka and Cx being sub- 

 stituted for K-b and C B , and Ch for Coh; the correction to the specific 

 conductance then becoming 



10- 3 [C H (A H + Aoh) + (Coh C H ) (A Na + Aoh)] 

 for sodium acetate, and 



10- 3 [Coh(A h + Aoh) + (C H Coh) (Ah + A Ac ) ] 

 for ammonium acetate. 



