Question

Which of the following is an indicator for Volhard determination of chloride? 

A. ferroin

B. none of the given answers

C. K2CrO4

D. fluorescein

E. ferric alum

Answer 1

In the method of Volhard determination of chloride ions, an excess of silver nitrate is added:

Ag⁺ + Cl^- $\rightarrow$ AgCl$\downarrow$ .

The excess of silver ions is then titrated with potassium thiocyanate:

Ag⁺ + SCN^- $\rightarrow$ AgSCN$\downarrow$ .

At the end point of the titration, the slight excess of SCN^- anions form a dark red complex with iron (III) cations that serve as the indicator:

SCN^- + Fe³⁺ $\rightarrow$ [Fe(SCN)]²⁺.

Among the substances proposed, ferric alum, or ferric ammonium sulfate NH₄Fe(SO₄)₂·12H₂O is the indicator for Volhard method of determination of chloride anions in solution.