A certain half-reaction has a standard reduction potential + 0.80 V. An engineer proposes using this half-reaction at the anode of a galvanic cell that must provide at least 0.9 V of electrical power. The cell will operate under standard conditions. Note for advanced students: assume the engineer requires this half-reaction to happen at the anode of the cell.

a. Is there a minimum standard reduction potential that the half-reaction used at the cathode of this cell can have?

b. Is there a maximum standard reduction potential that the half-reaction used at the cathode of this cell can have?

a. Minimum 1.70 V

b. There is no maximum.

Explanation:

We can solve this question by remembering that the cell potential is given by the formula

ε⁰ cell = ε⁰ reduction - ε⁰ oxidation

Now the problem states the cell must provide at least 0.9 V and that the reduction potential of the oxidized species 0.80 V, thus

ε⁰ reduction - ε⁰ oxidation ≥ ε⁰ cell

Since ε⁰ oxidation is by definition the negative of ε⁰ reduction, we have

ε⁰ reduction - (0.80 V) ≥ 0.90 V

⇒ ε⁰ reduction ≥ 1.70 V

Therefore,

(a) The minimum standard reduction potential is 1.70 V

(b) There is no maximum standard reduction potential since it is stated in the question that we want to have a cell that provides at leat 0.9 V