Understanding Matter: Pure Substances, Mixtures, and Solutions

Posted on Feb 18, 2025 in Chemistry

Matter: Pure Substances and Mixtures

Pure substances have a constant composition that does not change under any physical conditions. They cannot be broken down into simpler substances by physical means.

Pure Substances: Compounds and Elements

  • Compounds: Pure substances that can be broken down into simpler substances through chemical processes.
  • Elements: Pure substances that cannot be broken down into simpler substances by any means.

Mixtures

Mixtures are combinations of multiple pure substances that can be separated using physical methods.

Types of Mixtures

  • Heterogeneous Mixtures: Components are visible and distinguishable.
  • Homogeneous Mixtures (Solutions): Components are not visible and appear uniform.
  • Non-Homogeneous Mixtures: Scatter light.
  • Colloids: Heterogeneous mixtures that scatter light.
  • Emulsions: Colloids where particles are dispersed by an emulsifier.

Separation of Mixtures

  • Sieving: Separates solids with different particle sizes (e.g., sand and gravel).
  • Filtration: Separates insoluble solids from liquids (e.g., copper dichromate).
  • Crystallization: Separates a solid from a solvent (e.g., saline solution).
  • Magnetic Separation: Separates magnetic materials from non-magnetic materials (e.g., sulfur and iron filings).
  • Settling: Separates two immiscible liquids with different densities using a separatory funnel (e.g., oil and water).
  • Distillation: Separates two miscible liquids with different boiling points.
  • Chromatography: Separates components of a homogeneous mixture based on their affinity to a mobile phase (liquid or gas) and a stationary phase (solid).

Homogeneous Mixtures: Solutions

Solutions are homogeneous mixtures of two or more components.

Components of a Solution

  1. Solvent: The component present in the greater proportion.
  2. Solute: The component present in the lesser proportion.

Concentration of Solutions

The concentration of a solution is the amount of solute present in a certain amount of solution.

Percentage by Mass

Indicates the grams of solute in 100 grams of solution.

% by mass of solute = (mass of solute / mass of solution) x 100

Percentage by Volume

Indicates the volume of solute in 100 units of solution volume.

% by volume = (volume of solute / volume of solution) x 100

Mass Concentration

The amount of mass of solute in a unit volume of solution.

Mass concentration = mass of solute / volume of solution

Solubility

Solubility is the maximum amount of solute that can be dissolved in a given amount of solvent (e.g., grams of solute per 100 mL of solvent, or grams of solute per liter of solvent).

Types of Solutions Based on Solute Concentration

  1. Dilute Solution: Low solute-to-solvent ratio.
  2. Concentrated Solution: High solute-to-solvent ratio.
  3. Saturated Solution: Cannot dissolve any more solute.

The Atom: Historical Perspective

Democritus and Dalton

Leucippus and Democritus proposed that matter consists of indivisible particles called atoms (460-370 BC).

Plato and Aristotle believed that matter was a continuum that could be divided infinitely (428-348 BC).

Lavoisier and Dalton demonstrated that matter consists of atoms:

  1. Matter is composed of indivisible and indestructible atoms.
  2. All atoms of the same element are identical in mass and properties.
  3. Compounds are formed by combinations of atoms from different elements.

Substances in Life

  • Pure Water: Pure substance.
  • Blood: Heterogeneous mixture.
  • Plasma: Homogeneous mixture.