Equilibrium: Iron(III) as Indicator for Ag+ Concentration

[Intr3pid]

hi

I'm really having trouble with this question, can anyone help?

When Ag+ ions re added to the red FeSCN2+ ions, the color disappears, and white precipitate of AgSCn forms. Explain why the Iron(III) can be used aws an indicator in a reaction to determine the concentration of an unknown solution of Ag+ by reacting it with a solution of KSCN of known concentration. (the system is at equilibrium as well)

thanks

 

[Astronuc]

When Ag+ ions re added to the red FeSCN2+ ions, the color disappears, and white precipitate of AgSCn forms.

So what is the significance of this as it relates to using Fe as an indicator?

 

[GCT]

it's similar to the volhard titration, you titrated the unknown sample with the known standard of KSCN with iron(III) as an indicator, when the color disappears, you've reached the end point.