Question: why edta is ph dependent?
Answer: EDTA is insoluble in water at low pH because H4Y is predominant in that pH (less than 2). With increasing the pH, each hydrogen ion in the carboxyl groups of EDTA will start to dissociate. ... As we need Y4- to react with the metal ions present in the titration solution, we use pH 10 buffer such as ammonium chloride.