Ch.19 - Electrochemistry

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.19 - Electrochemistry

Problem 99

Chapter 19, Problem 99

What is the Fe2+: Sn2+ concentration ratio in the following cell at 25 °C if the measured cell potential is 0.35 V?

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Identify the half-reactions for the cell. The cell consists of Fe2+/Fe and Sn2+/Sn half-cells.

Write the standard reduction potentials for each half-reaction: Fe2+ + 2e- -> Fe (E° = -0.44 V) and Sn2+ + 2e- -> Sn (E° = -0.14 V).

Determine the overall cell reaction and calculate the standard cell potential (E°cell) using E°cell = E°cathode - E°anode.

Use the Nernst equation to relate the cell potential (Ecell) to the concentrations: Ecell = E°cell - (RT/nF) * ln(Q), where Q is the reaction quotient.

Solve for the concentration ratio [Fe2+]/[Sn2+] by rearranging the Nernst equation and substituting the given Ecell and calculated E°cell.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Nernst Equation

The Nernst Equation relates the cell potential to the concentrations of the reactants and products in an electrochemical cell. It is expressed as E = E° - (RT/nF) ln(Q), where E is the cell potential, 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 concentration ratio of ions based on the measured cell potential.

Cell Potential

Cell potential, or electromotive force (EMF), is the voltage generated by an electrochemical cell when it is operating. It indicates the tendency of the cell to drive an electrochemical reaction. The measured cell potential can provide insights into the relative concentrations of the reactants and products, which is essential for determining the concentration ratio of Fe2+ to Sn2+ in this specific cell.

Reaction Quotient (Q)

The reaction quotient (Q) is a dimensionless number that reflects the ratio of the concentrations of products to reactants at any point in a reaction, not necessarily at equilibrium. For the given cell, Q can be expressed as [Fe2+]/[Sn2+]. By substituting Q into the Nernst Equation, we can solve for the concentration ratio of Fe2+ to Sn2+ based on the measured cell potential.

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Textbook Question

Consider a galvanic cell that uses the reaction Calculate the potential at 25 °C for a cell that has the following ion concentrations: [Ag+] = 0.010M, [Ni2+] = 0.100M.

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Textbook Question

Given the following half-reactions and E° values, write a balanced equation for the formation of Mn2+ and MnO2 from Mn3+, and calculate the value of E° for this reaction. Is the reaction spontaneous under standard-state conditions?

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Textbook Question

The Nernst equation applies to both cell reactions and half-reactions. For the conditions specified, calculate the potential for the following half-reactions at 25 °C.(b)

Consider a galvanic cell that uses the following half-reactions: (b) What is the oxidizing agent, and what is the reducing agent?.

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Textbook Question

When suspected drunk drivers are tested with a Breathalyzer, the alcohol (ethanol) in the exhaled breath is oxidized to acetic acid with an acidic solution of potassium dichromate: The color of the solution changes because some of the orange Cr₂O₇^2-is converted to the green Cr³⁺ The Breathalyzer measures the color change and produces a meter reading calibrated in blood alcohol content. (a) What is E° for the reaction if the standard half-cell potential for the reduction of acetic acid to ethanol is 0.058 V?

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