Ch.19 - Electrochemistry

McMurry8th EditionChemistryISBN: 9781292336145당신이 사용하는 게 아니라요?교과서 변경

McMurry 8th Edition

Ch.19 - Electrochemistry

문제 101b

19장, 문제 101b

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. (b) What is the value of E for the reaction when the concentrations of ethanol, acetic acid, Cr₂O₇ are 1.0 M and the pH is 4.00?

검증된 단계별 안내

Identify the half-reactions involved in the redox process. Ethanol is oxidized to acetic acid, and dichromate ions are reduced to chromium ions.

Write the balanced half-reactions for the oxidation of ethanol to acetic acid and the reduction of Cr_2O_7^{2-} to Cr^{3+}.

Use the Nernst equation to calculate the cell potential (E) under non-standard conditions: E = E^0 - (RT/nF) * ln(Q), where Q is the reaction quotient.

Determine the standard cell potential (E^0) by using standard reduction potentials from a table for each half-reaction and combining them.

Calculate the reaction quotient (Q) using the given concentrations and pH, and substitute all known values into the Nernst equation to find E.

비슷한 문제에 대한 검증된 영상 답변:

이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.

영상 길이:

16m

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Redox Reactions

Redox reactions involve the transfer of electrons between two species, where one is oxidized (loses electrons) and the other is reduced (gains electrons). In the context of the Breathalyzer, ethanol is oxidized to acetic acid, while potassium dichromate is reduced, leading to a color change in the solution. Understanding the oxidation states of the involved species is crucial for analyzing the reaction.

Electrode Potential (E)

The electrode potential (E) is a measure of the tendency of a chemical species to be reduced, expressed in volts. It is determined under standard conditions but can be adjusted for concentration and pH using the Nernst equation. In this scenario, calculating E for the reaction requires knowledge of the standard reduction potentials and the concentrations of the reactants.

Nernst Equation

The Nernst equation relates the cell potential to the concentrations of the reactants and products at non-standard conditions. It is given by E = E° - (RT/nF)ln(Q), where E° is the standard 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 essential for calculating the actual electrode potential in the Breathalyzer reaction.

관련 실천

교과서 질문

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)

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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교과서 질문

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?

801

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교과서 질문

At one time on Earth, iron was present mostly as iron(II). Later, once plants had produced a significant quantity of oxygen in the atmosphere, the iron became oxidized to iron(III). Show that Fe2+(aq) can be spontaneously oxidized to Fe3+(aq) by O2(g) at 25°C assuming the following reasonable environmental conditions:

761

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