Question

Describe the titration of chloride by silver nitrate solution according to Volhard, and take into consideration the titrator, the indicator, its color, and the colors of the formed precipitates and complexes.

Answer 1

This is back titration. first we treat chloride ions with excess of measured silver nitrate solution forms AgCl as white prespitate.

Ag⁺_(excess) + Cl^- $\rightarrow$ AgCl_(s) + Ag⁺_(unreacted).

the unreacted Ag+ ions are titrated with saturated solution of thiocynate ion ferric alum as indiactor, colour change from pale yellow to red colour.

Ag⁺ + SCN^- $\rightarrow$ AgSCN_{(white solid)}

Fe⁺³ + SCN^- $\rightarrow$ FeSCN⁺²

chloride ions in AgCl is replaced by SCN^- forms AgSCN give error in end point to avoid this error before titrate with thiosynate solution filter the Agcl prespitte or use some organic liquids like chloroform its form film around prespitate.