11.2 Electrolytes

Electrolytes are substances that conduct electricity when dissolved in water. They dissociate into ions, with strong electrolytes fully breaking apart and weak ones only partially. This ionization process is crucial for understanding how chemicals behave in solution.

The strength of an electrolyte depends on its interactions with water molecules. Ionic compounds split into separate ions, while covalent electrolytes react with water. These processes are key to grasping how different substances dissolve and conduct electricity in aqueous solutions.

Electrolytes

Concept and examples of electrolytes

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• Electrolytes dissociate into ions when dissolved in water, allowing the solution to conduct electricity (conductivity)
  • Strong electrolytes completely dissociate into ions (NaCl, HCl, NaOH)
  • Weak electrolytes only partially dissociate into ions (CH3COOH, NH3)
• Non-electrolytes do not dissociate into ions and do not conduct electricity when dissolved (C12H22O11, C2H5OH)

Dissolution of ionic vs covalent electrolytes

• Ionic electrolytes (salts) dissociate into separate cations and anions when dissolved in water driven by the strong attraction between ions and water molecules
  • $NaCl(s) \rightarrow Na^+(aq) + Cl^-(aq)$
• Covalent electrolytes (acids and bases) undergo a reaction with water to form ions
  • Strong acids and bases completely react with water to form ions
    • $HCl(g) + H2O(l) \rightarrow H3O^+(aq) + Cl^-(aq)$
  • Weak acids and bases only partially react with water to form ions and undissociated molecules
    • $CH3COOH(l) + H2O(l) \rightleftharpoons CH3COO^-(aq) + H3O^+(aq)$

Solute-solvent interactions in electrolyte strength

• Electrolyte strength depends on the extent of its dissociation or ionization in water
• Solute-solvent interactions, such as ion-dipole interactions, determine electrolyte strength
  • Strong ion-dipole interactions between ions and water molecules lead to complete dissociation and strong electrolyte behavior
    • Ions with high charge density (small size and high charge) interact strongly with water and are strong electrolytes
  • Weak ion-dipole interactions result in partial dissociation and weak electrolyte behavior
    • Ions with low charge density (large size and low charge) interact weakly with water and are weak electrolytes
• Solvent polarity affects electrolyte strength
  • Polar solvents (water) promote dissociation and ionization due to their ability to solvate ions
  • Non-polar solvents (hexane) do not effectively solvate ions, leading to minimal dissociation and weak electrolyte behavior

Processes in electrolyte solutions

• Dissociation: The process by which ionic compounds separate into individual ions in solution
• Solvation: The surrounding of dissolved ions by solvent molecules, stabilizing them in solution
• Ionization: The process by which neutral molecules form ions in solution, often through reaction with the solvent
• Hydration: The specific form of solvation where water molecules surround and interact with dissolved ions