In a volumetric precipitation titration, ferric alum TS is used as an indicator when the titrant is which substance?

In a volumetric precipitation titration, ferric alum TS is used as an indicator when the titrant is which substance?

• A. AgNO3
• B. BaCl2
• C. NH4Cl
• D. NH4SCN

Answer: (A)

In volumetric precipitation titration, you detect the endpoint with an indicator that produces a visible change when the precipitating reaction has gone to completion. Ferric alum TS provides Fe3+ ions that form a distinct red complex with thiocyanate ions (FeSCN2+) once any free thiocyanate is left in solution. As you titrate, the analyte (for example, a halide) is precipitated by the titrant, typically Ag+, until all of it is consumed. After that point, the thiocyanate from the indicator is free to react with Fe3+, giving the characteristic red color that signals the endpoint. Therefore, the titrant being used is silver nitrate (AgNO3).

In volumetric precipitation titration, you detect the endpoint with an indicator that produces a visible change when the precipitating reaction has gone to completion. Ferric alum TS provides Fe3+ ions that form a distinct red complex with thiocyanate ions (FeSCN2+) once any free thiocyanate is left in solution. As you titrate, the analyte (for example, a halide) is precipitated by the titrant, typically Ag+, until all of it is consumed. After that point, the thiocyanate from the indicator is free to react with Fe3+, giving the characteristic red color that signals the endpoint. Therefore, the titrant being used is silver nitrate (AgNO3).