Consider a voltaic cell in which the following reaction occurs. $$ \mathrm{Zn}(s)+\mathrm{Sn}^{2+}(a q) \longrightarrow \mathrm{Zn}^{2+}(a q)+\mathrm{Sn}(s) $$ (a) Calculate \(E^{\circ}\) for the cell. (b) When the cell operates, what happens to the concentration of \(\mathrm{Zn}^{2+}\) ? The concentration of \(\mathrm{Sn}^{2+}\) ? (c) When the cell voltage drops to zero, what is the ratio of the concentration of \(\mathrm{Zn}^{2+}\) to that of \(\mathrm{Sn}^{2+}\) ? (d) If the concentration of both cations is \(1.0 \mathrm{M}\) originally, what are the concentrations when the voltage drops to zero?

Short Answer

Expert verified
In summary, the process for solving this exercise involved the following steps: (a) The E° for the cell was calculated as 0.62V, based on the standard reduction potentials of the half-reactions. (b) As the cell operates, the concentration of Zn²⁺ increases while the concentration of Sn²⁺ decreases. (c) The ratio of the concentrations of Zn²⁺ to Sn²⁺ when the voltage drops to zero was found using the Nernst equation: [Zn²⁺]/[Sn²⁺] = e^((0.62V * 2F) / RT). (d) The equilibrium concentrations of Sn²⁺ and Zn²⁺ can be determined by solving the equation numerically. The resulting concentrations will depend on the given temperature and initial concentrations, which were not provided in the question.

Step by step solution

01

Find the standard reduction potentials

To calculate the E° for the given cell, you'll first need the standard reduction potentials for the half-reactions: Zn (s) → Zn²⁺(aq) + 2e⁻ (oxidation) Sn²⁺(aq) + 2e⁻ → Sn (s) (reduction) You can find these values in a table of standard reduction potentials. The standard reduction potentials are: E°(Zn²⁺/Zn) = -0.76 V (a negative value denotes oxidation) E°(Sn²⁺/Sn) = -0.14 V (a negative value denotes reduction)
02

Calculate E° for the cell

Now that you have the standard reduction potentials for both half-reactions, you can calculate the E° for the cell by adding the two potentials together. E°cell = E°(reduction) - E°(oxidation) E°cell = (-0.14V) - (-0.76V) E°cell = 0.62V (a) The E° for the cell is 0.62V.
03

Determine changes in concentration

As the cell operates, Zn (s) is oxidized and Zn²⁺ (aq) is produced, so the concentration of Zn²⁺ increases. Concurrently, Sn²⁺(aq) gains electrons and is reduced to Sn(s), so the concentration of Sn²⁺ decreases. (b) Concentration of Zn²⁺ increases; concentration of Sn²⁺ decreases.
04

Calculate the ratio of concentrations when voltage drops to zero

When the cell voltage drops to zero, the reaction reaches equilibrium. You will use the Nernst equation to determine the ratio of concentrations: ΔE = E° - (RT/nF) lnQ Here, ΔE is the cell voltage, E° is the standard cell potential, R is the gas constant, T is the temperature in Kelvin, n is the number of electrons transferred (2 in this case), F is the Faraday constant, and Q is the reaction quotient. When the cell voltage drops to zero: 0 = 0.62V - (RT/2F) ln([Zn²⁺]/[Sn²⁺]) You can now rearrange the equation to find the ratio of concentrations: ln([Zn²⁺]/[Sn²⁺]) = (0.62V * 2F) / RT (c) The ratio of the concentration of Zn²⁺ to that of Sn²⁺: [Zn²⁺]/[Sn²⁺] = e^((0.62V * 2F) / RT)
05

Calculate the concentrations when the voltage drops to zero

Given that the initial concentrations of both cations (Zn²⁺ and Sn²⁺) were 1.0M: [Zn²⁺]/[Sn²⁺] = x / (1 - x) Where x is the concentration of Sn²⁺ at equilibrium and (1 - x) is the concentration of Zn²⁺ at equilibrium. You can now substitute the ratio of concentrations previously calculated: x / (1 - x) = e^((0.62V * 2F) / RT) Now, solve for x and (1 - x) numerically to find the equilibrium concentrations of Sn²⁺ and Zn²⁺: (d) The concentrations of Zn²⁺ and Sn²⁺ when the voltage drops to zero are obtained by solving the above equation numerically.

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Most popular questions from this chapter

Calculate \(E^{\circ}\) for the following cells: (a) \(\mathrm{Pb}\left|\mathrm{PbSO}_{4} \| \mathrm{Pb}^{2+}\right| \mathrm{Pb}\) (b) \(\mathrm{Pt}\left|\mathrm{Cl}_{2}\right| \mathrm{ClO}_{3}^{-} \| \mathrm{O}_{2}\left|\mathrm{H}_{2} \mathrm{O}\right| \mathrm{Pt}\) (c) \(\mathrm{Pt}\left|\mathrm{OH}^{-}\right| \mathrm{O}_{2} \| \mathrm{ClO}_{3}^{-}, \mathrm{Cl}^{-} \mid \mathrm{Pt} \quad\) (basic medium)

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For the following half-reactions, answer the questions below. $$ \begin{array}{cc} \mathrm{Co}^{3+}(a q)+e^{-} \longrightarrow \mathrm{Co}^{2+}(a q) & E^{\circ}=+1.953 \mathrm{~V} \\ \mathrm{Fe}^{3+}(a q)+e^{-} \longrightarrow \mathrm{Fe}^{2+}(a q) & E^{\circ}=+0.769 \mathrm{~V} \\ \mathrm{I}_{2}(a q)+2 e^{-} \longrightarrow 2 \mathrm{I}^{-}(a q) & E^{o}=+0.534 \mathrm{~V} \\ \mathrm{~Pb}^{2+}(a q)+2 e^{-} \longrightarrow \mathrm{Pb}(s) & E^{\circ}=-0.127 \mathrm{~V} \\ \mathrm{Cd}^{2+}(a q)+2 e^{-} \longrightarrow \mathrm{Cd}(s) & E^{\circ}=-0.402 \mathrm{~V} \\ \mathrm{Mn}^{2+}(a q)+2 e^{-} \longrightarrow \mathrm{Mn}(s) & E^{\circ}=-1.182 \mathrm{~V} \end{array} $$ (a) Which is the weakest reducing agent? (b) Which is the strongest reducing agent? (c) Which is the strongest oxidizing agent? (d) Which is the weakest oxidizing agent? (e) Will \(\mathrm{Pb}(s)\) reduce \(\mathrm{Fe}^{3+}(a q)\) to \(\mathrm{Fe}^{2+}(a q) ?\) (f) Will \(\mathrm{I}^{-}(a q)\) reduce \(\mathrm{Pb}^{2+}(a q)\) to \(\mathrm{Pb}(s) ?\) (g) Which ion(s) can be reduced by \(\mathrm{Pb}(s)\) ? (h) Which if any metal(s) can be oxidized by \(\mathrm{Fe}^{3+}(a q)\) ?

Consider the reaction $$ \mathrm{S}(s)+2 \mathrm{H}^{+}(a q)+2 \mathrm{Ag}(s)+2 \mathrm{Br}^{-}(a q) \longrightarrow 2 \mathrm{AgBr}(s)+\mathrm{H}_{2} \mathrm{~S}(a q) $$ At what \(\mathrm{pH}\) is the voltage zero if all other species are at standard concentrations?

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