Answer to Question #160637 in Chemistry for Dexther Villanueva

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.