Chapter 11: Solutions

Introduction to Solutions

• Focus on solution terminology
• Define electrolytes
• Learning outcomes and expectations

Types of Mixtures

Mixtures

• Broad definition: putting multiple substances together without changing their chemical composition.

Heterogeneous Mixtures

• Components not evenly distributed.
• Distinguishable boundaries (e.g., trail mix, sand and water).

Homogeneous Mixtures

• Components evenly distributed, resulting in a uniform appearance.
• Example: saltwater (visually indistinguishable).

Definition of Solution

• A homogeneous mixture of two components:
  • Solvent: the medium in larger quantity.
  • Solute: the substance dissolved in the solvent (usually in smaller quantity).
• Example: iced tea mix in water forms a solution.

Dissolution Process

• Dissolution: process of a solute dissolving in a solvent.
• Example: sodium chloride dissolving in water: Na+ and Cl- ions surrounded by water molecules.
• Terminology:
  • Soluble: ability to dissolve (e.g., salt in water).
  • Insoluble: inability to dissolve (e.g., sand in water).
• Miscible: two liquids that can completely dissolve in each other (e.g., ethanol and water).
• Immiscible: two liquids that cannot dissolve in each other (e.g., oil and water).

Solution Characteristics

• Solutions can be gases, liquids, or solids.
• Important to note: definition of solution is not limited to liquids.
• Example: gas-gas solutions (air), solid-solid solutions (brass).

Energetics of Solution Formation

• Formation is dictated by intermolecular forces and energy considerations:
  • Energy is required to break apart solute and solvent interactions.
  • New intermolecular forces form when substances mix.
• Favorable interactions lead to the formation of solutions.

Solubility Rules

• General rule: like dissolves like.
  • Nonpolar with nonpolar.
  • Polar with polar and ions.
  • Hydrogen bonding interactions enhance solubility.
• Example: sugar dissolves in water due to favorable hydrogen bonding.

Electrolytes

• Solutions can contain electrolytes: substances that yield ions when dissolved.
  • Non-electrolytes: do not yield ions (e.g., glucose, ethanol).
  • Electrolytes: dissociate into ions (e.g., NaCl, MgCl2).
• Strong electrolytes completely dissociate; weak electrolytes partially dissociate.

Conductivity and Electrolytes

• Conductivity of a solution provides a measure of electrolyte concentration.
• Pure water is a poor conductor; presence of ions increases conductivity.

Examples of Electrolytes

• Strong Electrolytes: salts, strong acids, strong bases (e.g., NaOH, KOH).
• Weak Electrolytes: weak acids and salts with small Ksp.

Conclusion

• Terminology associated with mixtures and solutions aids in discussions:
  • Mixture, homogeneous, heterogeneous, solute, solvent, solution, soluble, insoluble, miscible, immiscible, strong electrolyte, weak electrolyte.
• Next topic: solubility in upcoming sections (11.3).