Why mohr titration must be perform at a pH of neutral?
The reaction has to be carried out at neutral conditions because in acid the chromate indicator concentration decreases due to the reaction with the H+ ions, forming HCrO4-. It cannot be in too basic of a solution (greater than 10.5) because then silver hydroxide will form before the silver chromate can form.
I want to assmue the the readers of this answer have know the details theory and calculations about Mohr method if not u can refer to Any analytical text for reference. Well, Bromide and Chloride can not be determine simultaneously in a sample using Mohr method , the reason be that the indicator use for each of them is different. and there will be problem in the procedure if ones try to determine both simultaneously…
Why is it that mohr's method of titration for the determination of halide must be performed in neutral?
When pH is lower than 7, chromic ion gets protonated and chromic acid is predominant in the solution. Consequently, if the pH is above 7, chromate ion concentration is too low to form precipitate with silver ions at the end point. If the pH is above 10, brownish silver hydroxide is formed masking the end point. hence a neutral medium must be maintained