Ch.19 - Electrochemistry

McMurry8th EditionChemistryISBN: 9781292336145당신이 사용하는 게 아니라요?교과서 변경

McMurry 8th Edition

Ch.19 - Electrochemistry

문제 157

19장, 문제 157

A concentration cell has the same half-reactions at the anode and cathode, but a voltage results from different concentrations in the two electrode compartments. (b) A similar cell has 0.10 M Cu2+ in both compartments. When a stoichiometric amount of ethylenediamine (NH2CH2CH2NH2) is added to one compartment, the measured cell potential is 0.179 V. Calculate the formation constant Kf for the complex ion Cu(NH2CH2CH2CH2)22+. Assume there is no volume change.

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Identify the half-reaction for the copper concentration cell: Cu^{2+} + 2e^- \(\rightarrow\) Cu.

Recognize that the cell potential is due to the formation of the complex ion Cu(NH_2CH_2CH_2NH_2)_2^{2+} in one compartment.

Use the Nernst equation to relate the cell potential (E) to the concentrations: E = E^0 - \(\frac{RT}{nF}\) \(\ln\) Q, where Q is the reaction quotient.

Since the standard cell potential (E^0) for a concentration cell is 0, simplify the Nernst equation to: E = -\(\frac{RT}{nF}\) \(\ln\) Q.

Relate the reaction quotient Q to the formation constant K_f: Q = \(\frac{1}{K_f}\), and solve for K_f using the measured cell potential (0.179 V).

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주요 개념

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Concentration Cells

Concentration cells are electrochemical cells where the same half-reaction occurs at both the anode and cathode, but the potential difference arises from differing concentrations of reactants. The Nernst equation is used to relate the cell potential to the concentrations of the reactants, indicating that a higher concentration of reactants at one electrode leads to a greater tendency for reduction, thus generating voltage.

Formation Constant (Kf)

The formation constant (Kf) quantifies the stability of a complex ion in solution, representing the equilibrium between the free metal ion and the ligand-bound complex. It is calculated from the concentrations of the reactants and products at equilibrium, providing insight into how favorably a metal ion forms a complex with ligands, such as ethylenediamine in this case.

Nernst Equation

The Nernst equation relates the cell potential to the concentrations of the reactants and products in an electrochemical reaction. 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 is crucial for calculating the potential of concentration cells and understanding how changes in concentration affect cell voltage.

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교과서 질문

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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교과서 질문

Consider the redox titration (Section 4.13) of 120.0 mL of 0.100 M FeSO4 with 0.120 M K2Cr2O7 at 25 °C, assuming that the pH of the solution is maintained at 2.00 with a suitable buffer. The solution is in contact with a platinum electrode and constitutes one half-cell of an electrochemical cell. The other half-cell is a standard hydrogen electrode. The two half-cells are connected with a wire and a salt bridge, and the progress of the titration is monitored by measuring the cell potential with a voltmeter. (a) Write a balanced net ionic equation for the titration reaction, assuming that the products are Fe3+ and Cr3+.

370

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교과서 질문

The nickel–iron battery has an iron anode, an NiO(OH) cathode, and a KOH electrolyte. This battery uses the follow-ing half-reactions and has an E° value of 1.37 V at 25 °C. (b) Calculate ∆G° (in kilojoules) and the equilibrium con-stant K for the cell reaction at 25 °C.

1005

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교과서 질문

Consider a galvanic cell that utilizes the following half-reactions:

(b) What are the values of E° and the equilibrium constant K for the cell reaction at 25 °C?

651

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교과서 질문

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?

1607

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