When suspected drunk drivers are tested with a Breathalyzer, t...

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?

Accepted Answer

Identify the half-reactions involved in the Breathalyzer reaction. The oxidation half-reaction is the conversion of ethanol to acetic acid, and the reduction half-reaction is the conversion of $$Cr_{2}O$$_{7}^{2-} to $$Cr^{3+}.. $$Write the standard reduction potential for each half-reaction. The given standard reduction potential for the reduction of acetic acid to ethanol is 0.058 V. You will need to find the standard reduction potential for the $$Cr_{2}O$$_{7}^{2-} to $$Cr^{3+}$$ reaction from a standard reduction potential table.. Reverse the oxidation half-reaction to represent the oxidation of ethanol to acetic acid. Remember to change the sign of the standard reduction potential for this half-reaction since it is now an oxidation reaction.. Add the standard potentials of the two half-reactions to find the standard cell potential (E°) for the overall reaction. E° = E°(reduction) + E°(oxidation).. Ensure that the number of electrons lost in the oxidation half-reaction equals the number of electrons gained in the reduction half-reaction. If necessary, multiply the half-reactions by appropriate coefficients to balance the electrons before adding the potentials.

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Key Concepts

Standard Electrode Potentials

Redox Reactions

Nernst Equation