Class 12 Chemistry notes on Primary Batteries based on the NCERT syllabus:
Primary Batteries (Cells)
Definition:
Primary batteries are non-rechargeable electrochemical cells. They convert chemical energy into electrical energy and are meant for single-use only.
Characteristics:
- Irreversible chemical reactions
- Cannot be recharged
- Light and portable
- Used in devices with low current requirements
Common Example: Dry Cell (Leclanché Cell)
Construction:
- Anode: Zinc container (also acts as the cell body)
- Cathode: Carbon rod surrounded by powdered manganese dioxide (MnO₂) and carbon
- Electrolyte: Paste of ammonium chloride (NH₄Cl) and zinc chloride (ZnCl₂)
Reactions:
At Anode:
At Cathode:
Cell Voltage:
- Around 1.5 V
Another Example: Mercury Cell
- Used in watches, hearing aids, calculators
- Anode: Zinc (Zn)
- Cathode: Mercuric oxide (HgO)
- Electrolyte: Paste of KOH and ZnO
Reactions:
At Anode:
At Cathode:
- Voltage: ~1.35 V (constant output)
Advantages:
- Cheap and readily available
- Portable and convenient
- No need for maintenance
Limitations:
- Not rechargeable
- Limited lifespan
- Can leak after discharge
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