LAWS OF ELECTROLYTIC DISSOCIATION 83 



The partial solubility of tlie molecular species CaCOs is, inde- 

 pendently of the [H+], = X. Therefore, the total solubility is 



A = X + [Ca++] 



where [Ca++] is that concentration of Ca++ ions which is in equi- 

 librium with the CaCOs concentration X. This [Ca++] depends 

 upon [H+] in the following way: 



In solution there exists a state of equilibrium between calcium 

 monocarbonate and calcium bicarbonate. 



or 



Therefore, 



CaCOa + H2CO3 ;:± Ca(HC03)2 

 CaCOa + H2CO3 5:^ Ca++ + 2 HCO3- 



[CaCOs] [H2CO3] 



ki (1) 



[Ca++] [HC03-]2 

 But in the solution, [CaCOs] = X 



Furthermore, 



H2CO3 ^ H+ + HCO3- 

 hence 



Substituting in (1) the value of [H2CO3] found in (2), 



X X kj X [H+[ 



[Ca++] X [HCO3-] 



or, 



= ki 



tCa-]=^^X ^'^ 



ki [HCO3-] 



and 



X kj [H+ 



A = X + -— X 



ki [HCO3-] 



It is evident then that the solubility of CaCOa depends not only 

 upon the [H+] but also upon the concentration of the bicarbonate 



