Why do you have to filter AgCl before you can start back titration using the Volhard method?

Question

Why will you have to filter AgCl before you can start back titration? Is this also necessary for AgBr and AgI?

Answer 1

This method relies on precipitation of silver thiocyanate (AgSCN), but since the solubility of AgSCN is slightly less than that of AgCl, it’s possible for SCN^- to displace some Cl^-, from the previously precipitaed AgCl. Thus, you should filter the AgCl prior to titration. To know if you have to do the same with AgBr and AgI, look up their solubilities, and if the solubility of AgSCN is less, then the same problem exists, and you’ll have to filter them as well.