Question

To a metal nitrate, when $KI$ solution is added, a black precipitate is produced at first; on adding excess of $KI$, orange solution is produced. Identify the metal ion.

• A. $H{g}^{2+}$
• B. $B{i}^{3+}$
• C. $C{u}^{2+}$
• D. $P{b}^{2+}$

Answer 1

The correct option is B $B{i}^{3+}$

Since bismuth(III) iodide is insoluble in water, an aqueous solution can be tested for the presence of $B{i}^{3+}$ ions by adding a source of iodide such as potassium iodide. A black precipitate of bismuth(III) iodide indicates a positive test.

Bismuth(III) iodide forms iodobismuth(III) anions when heated with halide donors:

$2KI+Bi{I}_3\to K_2\left[Bi{I}_5\right]$ (orange solution)