Question

What type of battery is Mercury cell? Why it is more advantageous than dry cell? Write overall reaction taking place in Mercury cell.

Hint:

Mercury cells are ideal for small, low-current devices like digital watches and hearing aids where a stable voltage is essential for accuracy.

Answer 1

What type of battery is Mercury cell? Why it is more advantageous than dry cell? Write the overall reaction taking place in Mercury cell.

Solution:
The mercury cell is a type of primary battery, specifically a button cell, that uses mercury oxide (HgO) as the cathode material and zinc (Zn) as the anode. It is known for its compact size, consistent voltage, and long shelf life, making it ideal for use in small electronic devices such as hearing aids, watches, and cameras.
Advantages of Mercury Cell over Dry Cell:
1. Stable Voltage: Mercury cells provide a more stable and consistent voltage throughout their lifetime, whereas dry cells tend to show a gradual drop in voltage as they discharge.
2. Longer Shelf Life: Mercury cells have a much longer shelf life compared to dry cells. They can last for several years without significant loss of charge when stored properly.
3. Higher Energy Density: Mercury cells have a higher energy density, meaning they can store more energy in a smaller volume, making them ideal for portable devices that require small, lightweight power sources.
4. Low Self-Discharge Rate: Mercury cells have a lower self-discharge rate compared to dry cells, which means they lose charge at a slower rate when not in use.

Overall Reaction in Mercury Cell:
The overall reaction in a mercury cell involves the reduction of mercury oxide at the cathode and the oxidation of zinc at the anode. The reactions are as follows: At the anode (zinc electrode):

Zn → Zn²⁺ + 2e⁻

At the cathode (mercury oxide electrode):

HgO + H₂O + 2e⁻ → Hg + 2OH⁻

Overall cell reaction:

Zn + HgO → Hg + ZnO

This is the overall redox reaction taking place in the mercury cell, where zinc is oxidized to zinc ions, and mercury oxide is reduced to mercury, producing zinc oxide as the by-product.