Question

Question: By considering these half-reactions and their standard reduction potentials,

$$\begin{gathered} {\mathbf{\text{Pt}}}^{\mathbf{2}\mathbf{+}}\mathbf{+}\mathbf{2}{\mathit{e}}^{\mathbf{-}}\mathbf{\to }\mathbf{\text{Pt}}{\mathit{E}}^{\mathbf{0}}\mathbf{=}\mathbf{1}\mathbf{.}\mathbf{2}\mathbf{\text{V}} \\ {\mathbf{\text{Pt}}}^{\mathbf{2}\mathbf{+}}\mathbf{+}\mathbf{2}{\mathit{e}}^{\mathbf{-}}\mathbf{\to }\mathbf{\text{Pt}}\mathbf{}{\mathit{E}}^{\mathbf{0}}\mathbf{=}\mathbf{0}\mathbf{.}\mathbf{96}\mathbf{\text{V}} \\ {\mathbf{\text{PtCl}}}_{\mathbf{4}}^{\mathbf{2}\mathbf{-}}\mathbf{+}\mathbf{2}{\mathit{e}}^{\mathbf{-}}\mathbf{\to }\mathbf{\text{Pt}}\mathbf{+}\mathbf{4}{\mathbf{\text{Cl}}}^{\mathbf{-}}\mathbf{}{\mathit{E}}^{\mathbf{0}}\mathbf{=}\mathbf{0}\mathbf{.}\mathbf{73}\mathbf{\text{V}} \end{gathered}$$

Account for the fact that platinum will dissolve in a mixture of hydrochloric acid and nitric acid (aqua regia) but will not dissolve in either acid alone.

Short answer

Answer

The platinum will dissolve in mixture of hydrochloric acid and nitric acid as is evident in the.

Step-by-step solution

Half-cell potential.

Half-cell potential refers to the potential at the electrode of each half cell in an electrochemical cell. In an electrochemical cell, the total potential is calculated from the difference in potentials of two half cells.

${\text{∆E}}_{\text{cell}}{\text{=E}}_{\text{cathode}}{\text{-E}}_{\text{anode}}$

The Gibb’s energy for a electrochemical reaction is :

role="math" localid="1663661597163" $\text{∆G} \text{=} {\text{- nFE}}_{\text{cell}}$

if $∆G$is negative, the reaction is spontaneous.

Reaction in absence of  HCI

The complete reaction in absence of

$$\begin{gathered} 3\text{Pt}+2{\text{NO}}_3^{-}+8{\text{H}}_3{\text{O}}^{+}\to 3{\text{Pt}}^{2+}+2\text{NO}+12{\text{H}}_2\text{O} \\ {E}^0=E_{P{t}^{+2}/Pt}-E_{N{O_3}^{-}/NO} \\ =0.96-1.2 \\ =-0.24 \end{gathered}$$

The value is negative which means that is positive. So, reaction is not spontaneous.

Reaction in presence of  HCI

The rection in presence of

$$\begin{gathered} 3\text{Pt}+12{\text{Cl}}^{-}+2{\text{NO}}_3^{-}+8{\text{H}}_3{\text{O}}^{+}\to 3{\text{PtCl}}_4^{2-}+2\text{NO}+12{\text{H}}_2\text{O} \\ ∆E^0=0.96-0.73 \\ =0.23 \end{gathered}$$

The value is positive which means that is negative. So, reaction is spontaneous.