Question

Which of the following is a secondary cell?

• A. Leclanche cell
• B. Lead storage battery
• C. Concentration cell
• D. All of these

Hint:

Remember:
• Dry cell \( \rightarrow \) Primary cell
• Lead-acid battery \( \rightarrow \) Secondary cell Secondary cells are rechargeable because their reactions are reversible.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Electrochemical cells are classified into two main types based on their rechargeability:
Primary Cells: In these cells, the redox reaction occurs only once. After a period of use, the chemicals are exhausted, and the cell becomes "dead." It cannot be recharged by an external current because the chemical reactions are irreversible. Examples include the dry cell (Leclanche cell) and the mercury cell.
Secondary Cells: These cells can be recharged by passing a direct electric current through them in the opposite direction. This reverses the chemical reaction that occurred during discharge, restoring the original chemical composition. They can be used over many charge-discharge cycles.
Step 2: Detailed Explanation:
Let's analyze the given options:
1. Leclanche cell: This is the common dry cell used in portable devices like torches and clocks. It contains a zinc anode and a graphite cathode surrounded by \(MnO_{2}\) and \(NH_{4}Cl\). Once the zinc is oxidized and the \(MnO_{2}\) is reduced, the cell cannot be reused. Thus, it is a primary cell.
2. Lead storage battery: Commonly used in cars and as a backup power source (UPS). The anode is lead, and the cathode is a grid of lead packed with lead dioxide (\(PbO_{2}\)), immersed in sulfuric acid. The discharge reaction produces lead sulfate. By applying an external voltage, lead sulfate is converted back into lead and lead dioxide. Thus, it is a secondary cell.
3. Concentration cell: This is a specific type of galvanic cell where both half-cells have the same material (e.g., both are copper electrodes in \(CuSO_{4}\)), but the concentrations of the electrolytes differ. While it produces electricity, it is not commercially classified as a "secondary battery" or rechargeable storage cell.
Step 3: Final Answer:
The Lead storage battery is the correct example of a secondary cell.