The correct answer is option (2) Mercury cell.
A Mercury cell, also known as a mercuric oxide cell or a button cell, is a type of electrochemical cell that produces electrical energy through a chemical reaction. The specific reaction you provided occurs at the cathode of a Mercury cell. Let's break down the details:
Cathode Reaction:
\[ HgO + H_2O + 2e^- \longrightarrow Hg(l) + 2OH^- \]
Here's a detailed explanation:
1. Components:
\(HgO\) represents mercuric oxide, which is a compound containing mercury in an oxidized state.
\(H_2O\) is water.
\(2e^-\) represents two electrons.
2. Cathode (Reduction):
At the cathode (negative electrode) of the Mercury cell, reduction occurs. In this case, mercuric oxide (\(HgO\)) is reduced.
Mercuric oxide gains electrons (\(2e^-\)) and reacts with water to form mercury (\(Hg\)) and hydroxide ions (\(OH^-\)).
The overall effect is the conversion of mercuric oxide to liquid mercury and the generation of hydroxide ions.
3. Half-Reaction:
The cathode half-reaction is represented as: \(HgO + H_2O + 2e^- \longrightarrow Hg(l) + 2OH^-\)
4. Overall Cell Reaction:
The complete cell reaction involves both the anode and cathode reactions. The anode typically involves the oxidation of zinc.
The overall reaction can be represented as: \(Zn + HgO \longrightarrow ZnO + Hg\)
Mercury Cell:
Mercury cells are often used in small, button-sized batteries. The design typically includes a zinc anode, a paste of mercuric oxide (\(HgO\)), and an electrolyte (usually potassium hydroxide, \(KOH\)).
The zinc anode undergoes oxidation, releasing electrons. These electrons flow through an external circuit, providing electrical power for devices.
At the cathode, as you've described, mercuric oxide is reduced to form mercury and hydroxide ions.
Applications:
Mercury cells have been widely used in applications such as hearing aids, cameras, and various small electronic devices due to their stable voltage and long shelf life.
Note:
While Mercury cells have been historically used, it's important to mention that the use of mercury in batteries has raised environmental concerns due to the toxicity of mercury. In many modern applications, alternative battery technologies that do not contain mercury are preferred. Recycling programs are in place to properly handle the disposal of mercury-containing batteries. |
