In determination of chlorides using argentometric titration, what indicator shall be used?

• A. phenolphthalein
• B. ferroin
• C. methyl red
• D. potassium chromate

Answer: (D)

In argentometric titration of chlorides, the endpoint is detected by the formation of a silver chromate precipitate. As silver ions are added, chloride is first precipitated as AgCl until all chloride is consumed. Once no chloride remains, the next added silver ions react with chromate ions present in solution to form a distinct Ag2CrO4 precipitate, which has a reddish color and marks the endpoint. Potassium chromate is used because it provides the chromate ion needed for this sharp color change. Other indicators like phenolphthalein, methyl red, or ferroin respond to pH or redox changes and do not signal the specific precipitation endpoint of this method.