Lecture: Pure Substances, Mixtures, and Separations

Classification of Matter

• Matter can be classified into:
  • Pure Substances
  • Mixtures

Pure Substances

• Composed of only one type of particle.
• Characteristics:
  • Fixed and constant composition.
  • Fixed and constant properties (e.g., melting point, boiling point, density).
  • Cannot be separated by physical means.
• Purity Test:
  • Measure melting or boiling point.
  • Impurities usually lower melting point and raise boiling point.

Elements

• Simplest form of matter.
• Cannot be broken down by ordinary physical or chemical processes.
• Composed of atoms of one kind.
• Examples:
  • Silver (Ag) - individual atoms.
  • Nitrogen (N₂) - molecules of two nitrogen atoms.
• Total of 118 known elements, classified as metals or non-metals.

Compounds

• Formed from two or more different elements chemically bonded in fixed proportions.
• Example: Sodium chloride (NaCl) from sodium and chlorine.
• Properties of compounds differ from their constituent elements.
• Represented by chemical formulae (e.g., NaCl, H₂O).

Mixtures

• Consist of two or more substances (elements/compounds) physically combined.
• Components retain individual properties and are not chemically bonded.
• Characteristics:
  • Variable composition.
  • Variable properties.
  • Can be separated by physical means.

Homogeneous Mixtures

• Uniform composition and properties throughout.
• Components are indistinguishable.
• Example: Solutions.

Heterogeneous Mixtures

• Non-uniform composition.
• Distinguishable components (not always with naked eye).
• Includes suspensions and colloids.

Solutions

• Homogeneous mixtures, typically liquids.
• Components:
  • Solvent: Substance doing the dissolving (higher concentration).
  • Solute: Substance being dissolved (lower concentration).
• Types of Solutions:
  • Aqueous solutions (solvent is water).
  • Saturated solutions: No more solute can dissolve at a certain temperature.

Examples of Solutions

• Sea water: Solid in liquid.
• White vinegar: Liquid in liquid.
• Soda water: Gas in liquid.
• Air: Gas in gas.

Suspensions

• Heterogeneous mixtures with visible dispersed particles.
• Examples:
  • Mud in water (solid in liquid).
  • Oil in water (liquid in liquid).
  • Dust in air (solid in gas).

Colloids

• Heterogeneous mixtures with particles smaller than suspensions but larger than solutions.
• Types of Colloids:
  • Gel: Solid in liquid (e.g., gelatin).
  • Emulsion: Liquid in liquid (e.g., mayonnaise).
  • Foam: Gas in liquid (e.g., whipped cream).
  • Aerosol: Solid or liquid in gas (e.g., smoke, fog).

Particle Size Comparison

• Solutions: Smallest particles.
• Colloids: Intermediate particle size.
• Suspensions: Largest particles.