Which Mohr method indicator is used in silver nitrate titration?

• A. Potassium chromate
• B. Ferric alum TS
• C. Methyl orange
• D. Phenolphthalein

Answer: (A)

In argentometric titrations like the Mohr method, you need an indicator that signals the moment when all the chloride (or other halide) has been precipitated by silver ions, so that any further Ag+ reacts to form a distinct colored precipitate. Potassium chromate provides chromate ions that react with the excess silver to form silver chromate, which is brick-red. This visible color change marks the endpoint clearly, making it the best indicator for this titration.

The other options don’t work for this purpose. Methyl orange and phenolphthalein are pH indicators, so they rely on shifts in acidity/basicity rather than precipitation; silver nitrate titrations depend on a precipitation reaction and a specific colored end-point, not a pH change. Ferric alum TS is not used as the Mohr indicator.