Solutions, Suspensions, and Colloids

Suspensions

  • Particles in a solvent are so large they settle out unless stirred.
    • e.g., Muddy water

Colloids

  • Intermediate particle size between solutions and suspensions.
  • Particles remain suspended due to constant molecular movement.
    • e.g., Mayonnaise (oil droplets in water)

Tyndall Effect

  • Distinguishes colloids from solutions.
  • Light is scattered by colloidal particles in a transparent medium.
    • e.g., Headlight beam visible in fog.

Properties

  • Solutions: Homogeneous, small particle size (0.01-1 nm), do not separate or scatter light.
  • Colloids: Heterogeneous, intermediate particle size (1-1000 nm), scatter light (Tyndall effect).
  • Suspensions: Heterogeneous, large particle size (>1000 nm), particles settle, may scatter light.

Electrical Conductivity

  • Electrolytes conduct.
  • Covalent: No light.
  • Weak Acid: Fairly light.
  • Ionic: Light Bright.
  • Strong Acid: Brightest

Solubility

  • Amount of substance to form a saturated solution in a solvent at a specific temperature.
    • e.g., Sugar solubility: 204 g per 100 g of water at 20°C.
  • Expressed as grams of solute per 100 g of solvent.

Solubility Curves

  • On the line = Saturated.
  • Under the line = Unsaturated.
  • Above the line = Supersaturated (some undissolved).

Saturated vs. Unsaturated Solutions

  • Saturated: Contains max solute amount.
  • Unsaturated: Contains less solute than saturated under same conditions.

Supersaturated Solutions

  • Contains more solute than a saturated solution under the same conditions.
  • Disturbance or adding more solute causes crystallization.

Mass of Solute Added vs. Mass of Solute Dissolved

  • A: Unsaturated - more solute can dissolve.
  • B: Saturated - if the amount of solute added exceeds the solubility some solute remains undissolved

Dissolving Ionic Compounds

  • Water polarity important for forming solutions of ionic compounds.
  • Hydration: Solution process with water as the solvent.

Liquid Solutes and Solvents

  • "Like dissolves like" - polarity, IMF's, and bond types.
  • Immiscible: Liquids not soluble in each other.
  • Miscible: Liquids dissolve freely in any proportion.

Pressure Effects on Solubility

  • ↑ Pressure = ↑ Gas solubility.
  • ↓ Pressure = ↓ Gas solubility.

Temperature Effects on Solubility

  • ↑ Temperature usually ↓ gas solubility.
  • ↑ Temperature usually ↑ solubility of solids in liquids.

Concentration

  • Measure of solute amount in a solvent or solution.
  • Opposite of concentrated is dilute.

Colligative Properties

  • Solution properties depend on the number of solute particles (concentration).
  • ↑ Solute particles: ↓ Freezing point, ↑ Boiling point, ↓ Vapor pressure.

Solubility and Precipitate

  • Soluble: Ability to dissolve.
  • Precipitate: Insoluble solid from a liquid solution; forms when aqueous solutions mix.