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Electrochemical cells are an important part of Electrochemistry and an important area to study for the UP TGT Science Exam
Two important examples are the Leclanché cell and the lead storage battery. Understanding their components, electrodes, electrolytes, EMF and working can help you solve both direct and conceptual questions.
Let's understand these two cells in detail.
The Leclanché cell is a type of primary electrochemical cell.
Its important components include:
These are important facts for exam preparation because questions can directly ask about the electrolyte, electrode, function of MnO₂ or EMF of the cell.
MnO₂ acts as a depolarizer in the Leclanché cell.
Therefore, remember:
Leclanché Cell → MnO₂ → Depolarizer
The approximate EMF of a Leclanché cell is:
1.5 V
This is an important fact that can appear as a direct MCQ.
A lead storage battery is a secondary cell, which means it can be recharged.
Its important components are:
Unlike a primary cell, a lead storage battery can be recharged by supplying electrical energy.
A lead storage battery is called a secondary cell because its electrochemical reactions can be reversed during charging.
During discharge, the battery produces electrical energy. During charging, electrical energy is supplied to restore the active materials.
Therefore:
Leclanché Cell → Primary Cell
Lead Storage Battery → Secondary Cell
During discharge, the lead storage battery supplies electrical energy to an external circuit.
An important change during discharge is the formation of PbSO₄ at both electrodes. The practice material provided for this topic specifically tests the formation of PbSO₄ during discharge.
At the negative electrode, the reaction can be represented as:
Pb + SO₄²⁻ → PbSO₄ + 2e⁻
At the positive electrode, PbO₂ also undergoes a reaction resulting in the formation of PbSO₄.
The key point to remember is:
During discharge → PbSO₄ is formed at both electrodes.
The concentration of H₂SO₄ decreases during discharge.
This is an important conceptual point for UP PGT Chemistry preparation and is directly tested in the supplied practice material.
Remember:
Discharge of lead storage battery → H₂SO₄ concentration decreases
A lead storage battery can be recharged by supplying electrical energy.
During charging, the discharge process is reversed and the active materials are restored.
In simple terms:
Discharge → Chemical energy → Electrical energy
Charging → Electrical energy → Chemical energy
Understanding this difference is important when answering questions about primary and secondary cells.
The approximate EMF of one lead storage cell is:
2.0 V
This value is important for direct questions as well as numerical applications.
For example, if six lead storage cells are connected in series:
6 × 2 V = 12 V
Therefore:
Six cells in series → Approximately 12 V
The supplied practice material includes this type of question.
| Feature | Leclanché Cell | Lead Storage Battery |
|---|---|---|
| Type | Primary cell | Secondary cell |
| Electrolyte | NH₄Cl | H₂SO₄ |
| Electrode | Zn | Pb and PbO₂ |
| Depolarizer | MnO₂ | — |
| Approx. EMF | 1.5 V | 2.0 V per cell |
| Rechargeable | No | Yes |
| Important discharge product | — | PbSO₄ |
This comparison can help you quickly revise the most important differences between the two cells.
These are the major concepts covered in the supplied 20-question practice material.
Now that you have studied the concepts, test your understanding with the 20-question practice set based on Leclanché Cell and Lead Storage Battery.
📥 Download the Leclanché Cell & Lead Storage Battery Practice PDF
The practice set covers electrolytes, electrodes, EMF, primary and secondary cells, discharge and charging reactions, PbSO₄ formation, H₂SO₄ concentration and series connection of cells.
Try answering the questions yourself before checking the answer key.
The most important points to remember are:
Leclanché Cell:
NH₄Cl → Electrolyte
Zn → Anode
MnO₂ → Depolarizer
1.5 V → Approximate EMF
Lead Storage Battery:
Pb/PbO₂ → Electrodes
H₂SO₄ → Electrolyte
2.0 V → Approximate EMF per cell
PbSO₄ → Formed during discharge
H₂SO₄ concentration → Decreases during discharge
6 cells in series → Approximately 12 V
A clear understanding of these points, followed by regular MCQ practice, can make this part of Electrochemistry much easier to revise for the UP PGT Chemistry exam.
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