Pure Substances and Mixtures

Learning Objectives

• Distinguish between pure substances and mixtures.
• Identify mixtures as homogeneous or heterogeneous.

Pure Substances

• Definition: Contains only one kind of matter.
• Types:
  • Element: Single type of atom.
  • Compound: Made of molecules that are combinations of different atoms.
• Characteristics:
  • Fixed, definite set of properties.
  • Examples:
    • Lead (Pb) - Element, consists of lead atoms.
    • Oxygen gas (O2) - Element, consists of oxygen molecules.
    • Water (H2O) - Compound, consists of water molecules.
    • Ammonia (NH3) - Compound, consists of ammonia molecules.

Mixtures

• Definition: Combination of two or more pure substances.
• Characteristics:
  • Can be separated into component pure substances.
  • Substances retain individual properties.
  • Example: Mixing sodium and chlorine forms sodium chloride (table salt), different from each element's properties.

Types of Mixtures

Heterogeneous Mixture

• Composition is not uniform.
• Example: Vegetable soup - varying amounts of components in each spoonful.

Homogeneous Mixture (Solution)

• Composition is uniform.
• Behaves as a single substance.
• Example: Salt dissolved in water - appears as a single substance.

Examples and Exercises

• Example 3.5.3:

  • Soda water - Homogeneous mixture.
  • Iron filings and sulfur - Heterogeneous mixture.

• Exercise 3.5.3: Classify mixtures

  • Human body - Heterogeneous mixture.
  • An amalgam - Homogeneous mixture.

Categorizing Matter

• Figure 3.5.1: Relationships between types of matter and separation methods.
• Phase Definition: Part of a sample with uniform composition and properties.
• Pure substance or homogeneous mixture = single phase.
• Heterogeneous mixture = multiple phases (e.g., oil and water layers).

Examples

• Example 3.5.1: Classify substances

  • Filtered tea - Homogeneous mixture.
  • Orange juice - Heterogeneous mixture.
  • Compact disc - Heterogeneous mixture.
  • Aluminum oxide - Pure compound.
  • Selenium - Element.

• Exercise 3.5.1: Classify substances

  • White wine - Homogeneous mixture.
  • Mercury - Element.
  • Ranch-style salad dressing - Heterogeneous mixture.
  • Table sugar - Compound.

Additional Examples

• Example 3.5.2: Categorize matter

  • Saltwater - Homogeneous mixture.
  • Soil - Heterogeneous mixture.
  • Water - Compound.
  • Oxygen - Element.

• Exercise 3.5.2: Categorize matter

  • Coffee - Homogeneous mixture.
  • Hydrogen - Element.
  • An egg - Heterogeneous mixture.

Summary

• Matter Categories:
  • Pure substances: Constant composition and properties.
  • Mixtures: Physical combinations of elements/compounds.
• Mixtures Types:
  • Homogeneous: Not visually distinguishable.
  • Heterogeneous: Visually distinguishable.

Key Takeaways

• Pure substances: Single element or compound.
• Mixtures: Combinations of different substances.
• Homogeneous mixtures: Uniform, not visually distinct.
• Heterogeneous mixtures: Non-uniform, visually distinct.

Contributors

• Stephen Lower, Marisa Alviar-Agnew, Henry Agnew.