The solubility product for \(\operatorname{CuI}(s)\) is \(1.1 \times 10^{-12}\) . Calculate the value of \(\mathscr{E}^{\circ}\) for the half-reaction $$\mathrm{CuI}(s)+\mathrm{e}^{-} \longrightarrow \mathrm{Cu}(s)+\mathrm{I}^{-}(a q)$$

Short Answer

Expert verified
The standard electrode potential \((\mathscr{E}^{\circ})\) for the given half-reaction involving Copper Iodide (CuI) is approximately -0.152 V.

Step by step solution

01

Write the solubility product expression

First, we need to write down the solubility product expression for CuI as per the given solubility constant. The dissociation of CuI in water can be represented as: $$\mathrm{CuI}(s) \rightleftharpoons \mathrm{Cu}^{+}(a q)+\mathrm{I}^{-}(a q)$$ The solubility product expression for this reaction is: $$K_{sp} = [\mathrm{Cu}^{+}][\mathrm{I}^{-}]$$ Given, \(K_{sp} = 1.1 \times 10^{-12}\).
02

Identify the half-cell reaction and write its cell potential expression

The half-cell reaction given in the exercise is: $$\mathrm{CuI}(s)+\mathrm{e}^{-} \longrightarrow \mathrm{Cu}(s)+\mathrm{I}^{-}(a q)$$ The cell potential of this half-cell reaction can be written as per the Nernst equation, modified for a half-reaction: $$\mathscr{E}=\mathscr{E}^{\circ}-\frac{RT}{nF} \ln Q$$ Here, \(\mathscr{E}\) is the cell potential, \(\mathscr{E}^{\circ}\) is the standard electrode potential, R is the gas constant, T is the temperature, n is the number of moles of electrons transferred, F is the Faraday constant, and Q is the reaction quotient.
03

Relate \(K_{sp}\) to the half-cell reaction

In the given half-cell reaction, there is no \(\mathrm{Cu}^{+}\) ion, but we have the \(\mathrm{I}^{-}\) ion concentration. Our goal is to express \(\mathscr{E}^{\circ}\) in terms of given \(K_{sp}\). For the half-cell reaction, we can rewrite the cell potential expression like this: $$\mathscr{E}=\mathscr{E}^{\circ}-\frac{RT}{nF} \ln [\mathrm{I}^{-}]$$ At equilibrium, the cell potential \(\mathscr{E}\) is 0, and the reaction quotient Q becomes K (equilibrium constant). From the solubility product expression, we know \(K_{sp}=[\mathrm{Cu}^{+}][\mathrm{I}^{-}]\). Since in the half-cell reaction, we have only one mole of electrons transferred \((n=1)\), the modified Nernst equation becomes: $$0=\mathscr{E}^{\circ}-\frac{RT}{F} \ln [\mathrm{I}^{-}]$$
04

Solve for \(\mathscr{E}^{\circ}\)

Let's rearrange the equation to solve for \(\mathscr{E}^{\circ}\): $$\mathscr{E}^{\circ}=\frac{RT}{F} \ln [\mathrm{I}^{-}]$$ Now, relieving the relation between \(K_{sp}\) and \([\mathrm{I}^{-}]\): $$[\mathrm{I}^{-}] = \frac{K_{sp}}{[\mathrm{Cu}^{+}]}$$ Since in the half-cell reaction, we have one mole of \(\mathrm{CuI}\) dissociating into one mole of \(\mathrm{I}^{-}\) and one mole of \(\mathrm{Cu}^{+}\), we can assume \([\mathrm{Cu}^{+}] = [\mathrm{I}^{-}]\). Therefore, $$[\mathrm{I}^{-}] = \sqrt{K_{sp}} = \sqrt{1.1 \times 10^{-12}}$$ Plugging the values of R (8.314 J/mol K), T (298 K, assuming room temperature), F (96485 C/mol), and \([\mathrm{I}^{-}]\) into the equation, we get: $$\mathscr{E}^{\circ}=\frac{8.314 \times 298}{96485} \ln \sqrt{1.1 \times 10^{-12}}$$
05

Calculate the value of \(\mathscr{E}^{\circ}\)

Finally, calculate the value of \(\mathscr{E}^{\circ}\): $$\mathscr{E}^{\circ} \approx -0.152\,\text{V}$$ Hence, the standard electrode potential \((\mathscr{E}^{\circ})\) for the given half-reaction is approximately -0.152 V.

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