Matter Around Us: Pure Substances and Mixtures

Key Topics

1. Pure Substances
2. Classification of Elements
3. Mixtures
4. Homogeneous and Heterogeneous Mixtures
5. Solutions, Suspensions, and Colloids
6. Physical and Chemical Changes

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1. Pure Substances

• Definition: A form of matter with a uniform and unchanging composition.
• Categories:
  • Elements: Cannot be broken down further by chemical reactions.
  • Compounds: Made up of two or more elements that can be broken down by chemical reactions.

Elements

• Types: Metals, Non-metals, Metalloids
  • Metals: Malleable, ductile, good conductors of heat and electricity.
  • Non-metals: Poor conductors of heat and electricity.
  • Metalloids: Exhibit properties of both metals and non-metals.
  • Exceptions: Iodine (non-metal), Graphite (non-metal).

2. Mixtures

• Definition: Formed by the physical combination of two or more pure substances.
• Properties: Variable composition, can be separated easily by physical methods.

Types of Mixtures

• Homogeneous Mixture (Solution): Uniform composition; components cannot be distinguished easily.
  • Examples: Saltwater, Sugar water
• Heterogeneous Mixture: Non-uniform composition; components can be easily distinguished and separated.
  • Examples: Mixtures with visible particles, suspensions.

Solutions

• Components: Solute (minor component) and Solvent (major component)
• Properties: Particles are less than 1 nanometer, do not settle, cannot be separated by filtration.
• Examples: Saltwater, Sugar water
• Tyndall Effect: Visible path of light due to scattering by small particles.
• Types:
  • Unsaturated: Can dissolve more solute.
  • Saturated: No more solute can dissolve.
  • Supersaturated: Contains more dissolved solute than in a saturated solution.

Concentration of Solutions

• Dilution: Decreasing the concentration of solute by adding more solvent.
• Measurement:
  • Mass by Mass: (mass of solute / mass of solution) × 100
  • Volume by Volume: (volume of solute / volume of solution) × 100

3. Suspensions

• Definition: Heterogeneous mixture where solid particles are dispersed in a liquid or gas.
• Properties: Particles can be seen and separated by filtration, settle down when left undisturbed.

4. Colloids

• Definition: Mixture with particles larger than in a solution but smaller than in a suspension.
• Properties: Particles are dispersed and do not settle.
• Components: Dispersed phase and dispersion medium.
• Examples: Fog (liquid in gas), Milk (liquid in liquid)
• Tyndall Effect: Scattering of light by colloidal particles.

5. Changes in Matter

Physical Changes

• Definition: Changes in physical properties (size, shape, state) without changing chemical nature.
• Reversibility: Mostly reversible.

Chemical Changes

• Definition: Changes that alter the chemical properties and composition of a substance.
• Reversibility: Mostly irreversible.
  • Examples: Burning of wood, rusting of iron, rotting of an apple.

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Summary

• Matter can be pure substances or mixtures.
• Pure substances include elements and compounds, while mixtures can be homogeneous (solutions) or heterogeneous.
• Solutions, suspensions, and colloids have distinct properties and behaviors.
• Understanding physical and chemical changes helps in comprehending the nature of matter and its transformations.