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Ch.19 - Electrochemistry
McMurry - Chemistry 8th Edition
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Tutti i libri di testoMcMurry 8th EditionCh.19 - ElectrochemistryProblema 155b,c
Capitolo 19, Problema 155b,c

The reaction of MnO4– with oxalic acid (H2C2O4) in acidic solution, yielding Mn2+ and CO2 gas, is widely used to determine the concentration of permanganate solutions. (b) Use the data in Appendix D to calculate E° for the reaction. (c) Show that the reaction goes to completion by calculating the values of ∆G° and K at 25 °C. (H2C2O4) in acidic solution, yielding Mn2+ and CO2 gas, is widely used to determine the concentration of permanganate solutions.

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Identify the half-reactions involved in the redox process. For the given reaction, the reduction half-reaction is MnO4– + 8H+ + 5e– → Mn2+ + 4H2O, and the oxidation half-reaction is H2C2O4 → 2CO2 + 2H+ + 2e–.
Use the standard reduction potentials from Appendix D to find the E° values for each half-reaction. The standard reduction potential for MnO4– to Mn2+ is typically given, and you will need to reverse the sign for the oxidation of H2C2O4 to CO2.
Calculate the standard cell potential, E°, for the overall reaction by combining the half-reactions. Use the formula E° = E°(cathode) - E°(anode). Ensure that the number of electrons lost in the oxidation half-reaction equals the number gained in the reduction half-reaction by multiplying the half-reactions by appropriate coefficients.
Calculate the standard Gibbs free energy change, ΔG°, using the formula ΔG° = -nFE°, where n is the number of moles of electrons transferred in the balanced equation, F is the Faraday constant (approximately 96485 C/mol), and E° is the standard cell potential.
Determine the equilibrium constant, K, at 25 °C using the relationship between ΔG° and K: ΔG° = -RT ln K, where R is the universal gas constant (8.314 J/mol·K) and T is the temperature in Kelvin. Solve for K to show that the reaction goes to completion.

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Standard Electrode Potential (E°)

The standard electrode potential (E°) is a measure of the tendency of a chemical species to be reduced, measured under standard conditions. It is crucial for predicting the direction of redox reactions and calculating the overall cell potential. In this context, E° values for the half-reactions involving MnO4– and oxalic acid will help determine the feasibility of the reaction.
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Standard Cell Potential

Gibbs Free Energy (∆G°)

Gibbs Free Energy (∆G°) is a thermodynamic quantity that indicates the spontaneity of a reaction at standard conditions. A negative ∆G° value suggests that a reaction is spontaneous and will proceed to completion. In this case, calculating ∆G° for the reaction will provide insight into whether the reaction between MnO4– and oxalic acid is thermodynamically favorable.
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Gibbs Free Energy of Reactions

Equilibrium Constant (K)

The equilibrium constant (K) quantifies the ratio of the concentrations of products to reactants at equilibrium for a given reaction. It is related to Gibbs Free Energy by the equation ∆G° = -RT ln(K). A large K value indicates that products are favored at equilibrium, which, when calculated for the reaction, will confirm whether it goes to completion.
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Equilibrium Constant K
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The reaction of MnO4– with oxalic acid (H2C2O4) in acidic solution, yielding Mn2+ and CO2 gas, is widely used to determine the concentration of permanganate solutions. (a) Write a balanced net ionic equation for the reaction.

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The reaction of MnO4– with oxalic acid (H2C2O4) in acidic solution, yielding Mn2+ and CO2 gas, is widely used to determine the concentration of permanganate solutions. (d) A 1.200 g sample of sodium oxalate (Na2C2O4) is dissolved in dilute H2SO4 and then titrated with a KMnO4 solution. If 32.50 mL of the KMnO4 solution is required to reach the equivalence point, what is the molarity of the KMnO4 solution?

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