Addition of Cl- to the Ag E-pH System

Using the five steps outlined in the previous section, the effects of the addition of Cl on the Ag E-pH system will now be determined. 

Once the AG° (reaction) value is obtained, the K value can be calculated using Equation (8) from Chapter 2. 

Noting that the concentration of the insoluble compound is defined as 1, the K value is re-labeled as Ksp. 

and H2S are not pertinent species above the gray line that runs from 0.25 V on the left to —0.75 v on the right. Above this line the S , HS , and H2S have been oxidized to Sg and/or 04 and/or HS04, and then to 208 . Therefore, the E-pH diagrams for this Zn/S system will show that the shaded region above this line is irrelevant to sulfide precipitation. It should be noted that the ion is a weak base. Therefore, it is necessary to take into account that as the pH of the solution is lowered, the concentration of the ion will be lowered due to protonation. The pertinent protonation reactions and corresponding AG° values and AG° (reaction) values (in kj/mole) are 

From the AG°(reaction) values, the K values for the reactions can be calculated as follows  

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