Chemistry class 12th Primary_Batteries_Class_12_Chemistry

Primary Batteries - Class 12 Chemistry


### Introduction to Primary Batteries
Primary batteries are non-rechargeable electrochemical cells that convert chemical energy into
electrical energy.
Once their reactants are consumed, they cannot be recharged.


### Characteristics of Primary Batteries
1. **Single-use:** Cannot be recharged.
2. **Portable and lightweight.**
3. **Low-cost and widely available.**
4. **Limited lifespan and energy capacity.**


### Types of Primary Batteries


#### 1. Dry Cell (Leclanché Cell)
- **Anode:** Zinc (Zn)
- **Cathode:** Carbon (Graphite rod)
- **Electrolyte:** Ammonium chloride (NH4Cl) and Zinc chloride (ZnCl2) paste
- **Reactions:**
- At Anode: Zn -> Zn2+ + 2e-
- At Cathode: MnO2 + NH4+ + e- -> Mn(OH)3 + NH3
- **Uses:** Flashlights, remote controls, clocks.


#### 2. Mercury Cell
- **Anode:** Zinc amalgam (Zn-Hg)
- **Cathode:** Mercury(II) oxide (HgO) with graphite
- **Electrolyte:** Potassium hydroxide (KOH) + Zinc oxide (ZnO)
- **Reactions:**
- At Anode: Zn + 2OH- -> ZnO + H2O + 2e-
- At Cathode: HgO + H2O + 2e- -> Hg + 2OH-
- **Uses:** Watches, hearing aids, medical instruments.


#### 3. Alkaline Battery
- **Anode:** Zinc (Zn)
- **Cathode:** Manganese dioxide (MnO2)
- **Electrolyte:** Potassium hydroxide (KOH)