Question

One of the commonly used electrode is calomel electrode. Under which of the following categories calomel electrode comes ?

• A. Metal – Insoluble Salt – Anion electrodes
• B. Oxidation – Reduction electrodes
• C. Gas – Ion electrodes
• D. Metal ion – Metal electrodes

Answer 1

The Correct Option is A

Understanding the Calomel Electrode:

The calomel electrode is commonly used as a reference electrode in electrochemical measurements. It consists of mercury (\( \text{Hg} \)) in contact with mercurous chloride (calomel, \( \text{Hg}_2\text{Cl}_2 \)) in a saturated potassium chloride (\( \text{KCl} \)) solution.

Category of the Calomel Electrode:

The calomel electrode falls under the category of "Metal – Insoluble Salt – Anion electrodes" because it involves a metal (\( \text{Hg} \)), an insoluble salt (\( \text{Hg}_2\text{Cl}_2 \)), and the chloride ions (\( \text{Cl}^- \)) in solution.

Conclusion:

The correct answer is Option (1): Metal – Insoluble Salt – Anion electrodes.

Answer 2

Step 1: Introduction to Calomel Electrode.
The calomel electrode is commonly used as a reference electrode in electrochemical measurements. It consists of mercury (Hg) in contact with mercurous chloride (Hg\(_2\)Cl\(_2\), called calomel) and a saturated solution of potassium chloride (KCl).

Step 2: Electrode Classification.
Electrodes are classified based on their constitution into several types, including metal-metal ion electrodes, gas electrodes, redox electrodes, metal-metal salt electrodes, amalgam electrodes, and ion-selective electrodes.
The calomel electrode specifically falls under the category of "Metal – Insoluble Salt – Anion electrode". This means:
- It contains a metal (mercury).
- It contains an insoluble salt phase (mercurous chloride, Hg\(_2\)Cl\(_2\)).
- The electrode reaction involves an anion (chloride ion, Cl\(^-\)).

Step 3: Working Principle.
The calomel electrode operates based on the equilibrium:
\[ \text{Hg}_2\text{Cl}_2 (s) + 2 e^- \rightleftharpoons 2 \text{Hg} (l) + 2 \text{Cl}^- \] The potential of the electrode depends on the chloride ion concentration in the solution.

Step 4: Importance and Applications.
Calomel electrodes provide a stable and reproducible reference potential and are widely used in pH measurements, potentiometric titrations, and electrochemical research.

Final Answer:
\[ \boxed{ \text{Metal – Insoluble Salt – Anion electrodes} } \]