In chemistry, many substances, when dissolved in water produce ions and allow the solution to conduct electricity. Such substances are known as electrolytes. However, all electrolytes do not behave in the same way. Some substances break completely into ions, while others break only partially. This difference in the extent of ionisation leads to the classification of electrolytes into strong and weak electrolytes.
Electrolytes
Electrolytes are substances that dissociate into ions when dissolved in water and allow the solution to conduct electricity. Electrolytes can be strong or weak. Conductivity depends on number of ions present
When an electrolyte dissolves in water:
- It breaks into positive and negative ions
- These ions carry electric current
Examples:
- HCl → H + + Cl ⁻ (acid)
- NaOH → Na ⁺ + OH - (base)
Strong Electrolyte
A strong electrolyte is a substance that completely ionises (dissociates) into ions when dissolved in water.
When a strong electrolyte is added to water:
- Almost all the molecules break into positive and negative ions
- There are no (or very few) undissociated molecules left
- The solution contains a large number of ions
- Because of this, the solution shows high electrical conductivity.
Examples:
- HCl → H ⁺ + Cl ⁻
- HNO3 → H ⁺ + NO3 ⁻
- NaOH → Na ⁺ + OH ⁻
- KCl → K ++ Cl ⁻
Characteristics of Strong Electrolyte
Strong electrolytes show the following important properties:
- Complete Ionisation: Strong electrolytes completely dissociate into ions in aqueous solution. Almost all molecules form ions.
- Large Number of Ions: They produce a high concentration of ions in solution. More ions give better conductivity.
- High Electrical Conductivity: Due to the presence of many ions, their solutions are good conductors of electricity.
- Degree of Ionisation: The degree of ionisation (α) is almost equal to 1. This means nearly 100% ionisation.
- No Significant Equilibrium: Ionisation is almost complete, so no strong equilibrium exists between ions and molecules.
Weak Electrolyte
A weak electrolyte is a substance that partially ionises (dissociates) into ions when dissolved in water.
When a weak electrolyte is added to water:
- Only a small fraction of molecules break into ions
- Most of the substance remains as undissociated molecules
- So, the solution contains fewer ions
- Because of this, the solution shows low electrical conductivity.
Examples:
- CH3COOH (acetic acid)
- NH4OH (ammonium hydroxide)
- HF (hydrofluoric acid)
Characteristics of Weak Electrolytes
Weak electrolytes show the following important properties:
- Partial Ionisation: Weak electrolytes partially dissociate into ions in aqueous solution.Only a small fraction forms ions.
- Small Number of Ions: They produce a low concentration of ions in solution. Fewer ions present.
- Low Electrical Conductivity: Due to fewer ions, their solutions are poor conductors of electricity.
- Degree of Ionisation: The degree of ionisation (α) is less than 1. Only partial ionisation occurs.
- Presence of Equilibrium: A dynamic equilibrium exists between ions and undissociated molecules.
Strong Electrolyte vs Weak Electrolyte
The differences between Strong and Weak Electrolyte are tabulated below:
| Strong Electrolyte | Weak Electrolyte |
|---|---|
| Completely dissociate in aqueous solution | Partially dissociate in aqueous solution |
| High electrical conductivity | Low electrical conductivity |
| Ostwald’s dilution law not applicable | Ostwald’s dilution law applicable |
| Weak interionic interactions | Strong interionic interactions |
| Completely ionized in solution or molten form | Partially ionized in solution or molten form |
| Examples: Strong acids, strong bases, salts | Examples: Weak acids, weak bases |