Which precipitation method uses potassium chromate as indicator with silver nitrate standard solution?

Which precipitation method uses potassium chromate as indicator with silver nitrate standard solution?

• A. Volhard
• B. Mohr
• C. Fajans
• D. All of the above

Answer: (B)

At the heart of this question is how a silver nitrate titration detects its end point using a specific indicator. In the Mohr method, you determine chloride by titrating a known sample with a standard silver nitrate solution in a neutral to slightly alkaline medium. Potassium chromate is added as the indicator. Early in the titration, silver ions react with chloride to form the white precipitate silver chloride, removing Ag+ from the solution. When all chloride has been precipitated, the next bit of silver ions reacts with chromate to form a brick-red precipitate of silver chromate, signaling the end point. This distinct color change makes the Mohr method reliable for detecting the completion of the reaction. The other argentometric methods use different indicators or approaches (adsorptive indicators in Fajans; back-titration in Volhard), so they don’t use potassium chromate in the same way.