Which statement best describes how a concentration cell generates an electric current?

• A. It relies on the use of different metals in each electrode to create a potential difference.
• B. It produces current by converting chemical energy from a fuel into electrical energy.
• C. It requires an external power source to drive the redox reaction.
• D. It uses the difference in ion concentrations between two half-cells to produce a voltage.

Answer: (D)

Verified step by step guidance

1. Understand that a concentration cell is a type of galvanic cell where both electrodes are made of the same metal, but the ion concentrations in the two half-cells differ.
2. Recognize that the potential difference (voltage) in a concentration cell arises due to the difference in ion concentration, not because of different metals or an external power source.
3. Recall the Nernst equation, which relates the cell potential to the concentration of ions: \(E = E^\circ - \frac{RT}{nF} \ln Q\), where \(Q\) is the reaction quotient involving ion concentrations.
4. In a concentration cell, the standard electrode potential \(E^\circ\) is zero because the electrodes are identical, so the cell potential depends solely on the concentration difference.
5. Therefore, the electric current is generated as ions move to equalize concentration differences, producing a voltage based on the ion concentration gradient between the two half-cells.