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Understanding Matter: Pure Substances and Mixtures

Dec 3, 2024

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.