Breathalyzers are used to test the amount of blood alcohol level in the exhaled breath of suspected drunk drivers. An acidic solution of potassium dichromate is usually used to oxidize alcohol (ethanol) to acetic acid. In an experiment, an acidic solution of potassium permanganate was used rather than potassium dichromate.
5 CH3CH2OH(aq) [ethanol] + 4 MnO4−(aq) + 12 H+(aq) → 5 CH3CO2H(aq) [acetic acid] + 4 Mn2+(aq) + 11 H2O(l)
Potassium permanganate changes color from a deep purple to a colorless solution after being reduced. The Breathalyzer can measure this change in color to get a reading of how much alcohol is in the blood. Determine the potential of the reaction if the concentrations of ethanol, acetic acid, MnO4−, and Mn2+ is 1.5 M and the pH of the solution is 4.50. (E°red,CH3CO2H = 0.058 V; E°red,MnO4− = 1.51 V)
