[patski]

I need your help regarding this method in determination of COD in water samples. As I know, sulfuric acid-silver sulfate solution was added to dissolved mercuric sulfate that was previously added to the sample. Needed volume of sulfuric acid-silver sulfate solution to be added is 75ml. 5ml is added directly to the sample and the remaining 70ml is added through the open end of condenser (set-up for reflux) - before the reflux starts.
Question: What is the significance of having the H2SO4-Ag2SO4 solution added separately (5ml directly to the sample, 70ml is through the end of condenser)? Is it okay if the whole required volume of the solution is added just one time? What are the possible effects?
Thanks!!!