Question

When aqueous KI is added gradually to mercury(II) nitrate, an orange precipitate forms. Continued addition of KI causes the precipitate to dissolve. Write balanced equations to explain these observations. (Hint: Hg²⁺ reacts with ${\mathbf{I}}^{\mathbf{-}}$to form HgI₄^2-,) would you expect HgI₄^2-to form coloured solution? Explain

Short answer

Mercury(II) Nitrate reacts with KI to form orange precipitate HgI₂. On continued addition, it forms K₂HgI₄called Nessler's reagent which is soluble in water.

Step-by-step solution

Step 1

Equations representing the solution

Mercury(II) nitrate reacts with KI to form orange precipitate ofHgI₂

_{$\mathrm{Hg}{\left({\mathrm{NO}}_3\right)}_2+2\mathrm{KI}\to {\mathrm{HgI}}_2$}

Step 2

HgI₂ reacts with KI to form Nessler’s reagent, which is soluble in water.

${\mathrm{HgI}}_2+2\mathrm{KI}\to {\mathrm{K}}_2{\mathrm{HgI}}_4$