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)

The Nernst equation is applicable not just to cell reactions, but also to half-reactions. Consider the following half-reaction, 

2 Hg²⁺(aq) + 2 e⁻ → 2 Hg₂²⁺(aq)       E° = 0.92 V

Using the Nernst equation, what is its potential at 25 °C if [Hg²⁺] = [Hg₂²⁺] = 0.15 M?

The overall reaction for a a voltaic cell is Co²⁺(aq) + Ni(s) → Co(s) + Ni²⁺(aq). The cell potential is +0.16 V when the concentration of Co²⁺ in the cathode is 1.5 M. Calculate the concentration of Ni²⁺ in the anode half-cell for this case.

Ni²⁺(aq) + 2 e^– → Ni(s)     E° = –0.26 V
Co²⁺(aq) + 2 e^– → Co(s)   E° = –0.28 V

Calculate the change in cell voltage when the ion concentrations in the half-cell of the cathode is increased by a factor of 100 for the following voltaic cell.

A voltaic cell initially consists of a 0.0250 M Mg/Mg²⁺ half-cell and a 1.32 M Ag/Ag⁺ half-cell. Calculate the cell potential when the Ag⁺ has already dropped to 3.18 V.

A voltaic cell initially consists of a 0.0250 M Mg/Mg²⁺ half-cell and a 1.32 M Ag/Ag⁺ half-cell. Calculate the cell potential when the Ag⁺ has already dropped to 0.50 M.

Calculate the pH needed for a standard hydrogen electrode to have an electrode potential of -0.153 V