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Ch.19 - Electrochemistry
Tro - Chemistry: A Molecular Approach 4th Edition
Tro4th EditionChemistry: A Molecular ApproachISBN: 9780134112831Non è quello che usi tu?Cambia libro di testo
Capitolo 19, Problema 112

The cell potential of this electrochemical cell depends on the gold concentration in the cathode half-cell. Pt(s) | H2(g, 1.0 atm) | H+(aq, 1.0 M) || Au3+(aq, ? M) | Au(s) What is the concentration of Au3+ in the solution if Ecell is 1.22 V?

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Identify the half-reactions for the electrochemical cell. The anode half-reaction involves hydrogen: \( \text{H}_2(g) \rightarrow 2\text{H}^+(aq) + 2e^- \). The cathode half-reaction involves gold: \( \text{Au}^{3+}(aq) + 3e^- \rightarrow \text{Au}(s) \).
Write the Nernst equation for the cell potential: \( E_{cell} = E^\circ_{cell} - \frac{RT}{nF} \ln Q \), where \( Q \) is the reaction quotient.
Determine the standard cell potential \( E^\circ_{cell} \) using standard reduction potentials: \( E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode} \). Use standard reduction potentials for \( \text{Au}^{3+}/\text{Au} \) and \( \text{H}^+/\text{H}_2 \).
Calculate the reaction quotient \( Q \) using the Nernst equation: \( Q = \frac{1}{[\text{Au}^{3+}]} \) since the concentration of \( \text{H}^+ \) is 1.0 M and \( \text{H}_2 \) is at 1.0 atm.
Rearrange the Nernst equation to solve for \( [\text{Au}^{3+}] \): \( [\text{Au}^{3+}] = \exp\left(\frac{nF(E^\circ_{cell} - E_{cell})}{RT}\right) \). Substitute known values to find the concentration of \( \text{Au}^{3+} \).

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Nernst Equation

The Nernst Equation relates the cell potential (E) of an electrochemical cell to the concentrations of the reactants and products. It is expressed as E = E° - (RT/nF) ln(Q), where E° is the standard cell potential, R is the gas constant, T is the temperature in Kelvin, n is the number of moles of electrons transferred, F is Faraday's constant, and Q is the reaction quotient. This equation allows us to calculate the cell potential under non-standard conditions, which is essential for determining the concentration of Au3+ in this scenario.
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The Nernst Equation

Standard Electrode Potentials

Standard electrode potentials (E°) are measured under standard conditions (1 M concentration, 1 atm pressure, and 25°C) and provide a reference for predicting the direction of redox reactions. Each half-reaction has a specific E° value, which can be used to calculate the overall cell potential. In this question, knowing the standard reduction potential for the Au3+/Au couple is crucial for determining the concentration of Au3+ when the cell potential is given.
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Standard Cell Potential

Reaction Quotient (Q)

The reaction quotient (Q) is a measure of the relative concentrations of products and reactants at any point in a reaction. It is calculated using the formula Q = [products]/[reactants], where the concentrations are raised to the power of their coefficients in the balanced equation. In this electrochemical cell, Q will include the concentration of Au3+ and the concentration of H+ ions, and it is essential for applying the Nernst Equation to find the unknown concentration of Au3+ when the cell potential is specified.
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Reaction Quotient Q