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: $\mathit{H}{\mathit{g}}^{\mathbf{2}\mathbf{+}}$
reacts with ${\mathit{I}}^{\mathbf{-}}$to form $\mathit{H}\mathit{g}{\mathit{l}}_{\mathbf{4}}^{\mathbf{2}\mathbf{-}}$.)

Short answer

Answer

Thebalanced equations are.

$$\begin{gathered} \mathbf{2}\mathit{K}\mathit{l}\left(aq\right)\mathbf{}\mathbf{}\mathbf{+}\mathbf{}\mathbf{}\mathit{H}\mathit{g}{\left(N{O}_3\right)}_{\mathbf{2}}\left(aq\right)\mathbf{}\mathbf{}\mathbf{\to }\mathbf{}\mathbf{}\mathit{H}\mathit{g}{\mathit{l}}_{\mathbf{2}}\left(s\right)\mathbf{}\mathbf{}\mathbf{}\mathbf{+}\mathbf{}\mathbf{}\mathbf{}\mathbf{2}\mathit{K}\mathit{N}{\mathit{O}}_{\mathbf{3}}\left(aq\right) \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathit{o}\mathit{r}\mathit{a}\mathit{n}\mathit{g}\mathit{e} \end{gathered}$$

$$\begin{gathered} \mathit{H}\mathit{g}{\mathit{l}}_{\mathbf{2}}\mathbf{\left(}\mathbf{s}\mathbf{\right)}\mathbf{+}\mathbf{2}{\mathit{l}}^{\mathbf{-}}\mathbf{\left(}\mathbf{aq}\mathbf{\right)}\mathbf{\to }\mathit{H}\mathit{g}{{\mathit{l}}_{\mathbf{2}}}^{\mathbf{2}\mathbf{-}}\mathbf{\left(}\mathbf{aq}\mathbf{\right)} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{\left(}\mathbf{Kl}\mathbf{\right)} \end{gathered}$$

Step-by-step solution

Reaction for the formation of an orange color precipitate.

The KI can be added to mercury (II) nitrate. The compound $\mathit{H}\mathit{g}{\left(N{O}_3\right)}_{\mathbf{2}}$will result in the formation of an orange color precipitate.

$$\begin{gathered} \mathbf{2}\mathit{K}\mathit{I}\left(aq\right)\mathbf{}\mathbf{}\mathbf{+}\mathbf{}\mathbf{}\mathit{H}\mathit{g}{\left(N{O}_3\right)}_{\mathbf{2}}\left(aq\right)\mathbf{}\mathbf{}\mathbf{}\mathbf{\to }\mathbf{}\mathbf{}\mathbf{}\mathit{H}\mathit{g}{\mathit{l}}_{\mathbf{2}}\left(s\right)\mathbf{}\mathbf{}\mathbf{+}\mathbf{}\mathbf{}\mathbf{2}\mathit{K}\mathit{N}{\mathit{O}}_{\mathbf{3}}\left(aq\right) \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathit{o}\mathit{r}\mathit{a}\mathit{n}\mathit{g}\mathit{e} \end{gathered}$$

The continued addition of KI causes the precipitate to dissolve.

In writing the ionic equation,

$\mathbf{2}{\mathit{K}}^{\mathbf{+}}\left(aq\right)\mathbf{+}\mathbf{2}{\mathit{l}}^{\mathbf{-}}\left(aq\right)\mathbf{+}\mathit{H}{\mathit{g}}^{\mathbf{2}\mathbf{+}}\left(aq\right)\mathbf{+}\mathbf{2}\mathit{N}{{\mathit{O}}_{\mathbf{3}}}^{\mathbf{-}}\left(aq\right)\mathbf{}\mathbf{\to }\mathit{H}\mathit{g}{\mathit{l}}_{\mathbf{2}}\left(s\right)\mathbf{+}\mathbf{2}{\mathit{K}}^{\mathbf{+}}\left(aq\right)\mathbf{+}\mathbf{2}\mathit{N}{{\mathit{O}}_{\mathbf{3}}}^{\mathbf{-}}\left(aq\right)$

On canceling spectator ions to get the overall equation,

$$\begin{gathered} \mathit{H}{\mathit{g}}^{\mathbf{2}\mathbf{+}}\left(aq\right)\mathbf{+}\mathbf{2}{\mathit{l}}^{\mathbf{-}}\left(aq\right)\mathbf{\to }\mathit{H}\mathit{g}{\mathit{l}}_{\mathbf{2}}\left(s\right) \\ \mathit{H}\mathit{g}{\mathit{l}}_{\mathbf{2}}\left(s\right)\mathbf{+}\mathbf{2}{\mathit{l}}^{\mathbf{-}}\left(aq\right)\mathbf{\to }\mathit{H}\mathit{g}{{\mathit{l}}_{\mathbf{4}}}^{\mathbf{2}\mathbf{-}}\left(aq\right) \end{gathered}$$

This orange precipitate of $\mathit{H}\mathit{g}{\mathit{l}}_{\mathbf{2}}\left(s\right)$is dissolved and transformed into a pale solution of $\mathit{H}\mathit{g}{{\mathit{l}}_{\mathbf{4}}}^{\mathbf{2}\mathbf{-}}\left(aq\right)$.