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Chapter 14: Solutions

14.4: Suspensions and Colloids

Suspension
A heterogeneous mixture with large particles that remain suspended for a period but eventually settle out over time.
Colloid
A heterogeneous mixture with medium-sized particles that remain dispersed and do not settle.
Tyndall Effect
The scattering of light by colloidal particles, making a beam of light visible in the mixture.
Brownian Motion
The random movement of colloidal particles due to collisions with molecules in the dispersing medium.
Dispersed Phase
The particles that remain suspended in a colloid.
Dispersing Medium
The continuous phase in which the dispersed particles are evenly distributed.

Properties of Suspensions and Colloids

  • Suspensions: Large particles, heterogeneous, particles settle over time, can be separated by filtration.
  • Colloids: Medium-sized particles, heterogeneous, do not settle out, exhibit the Tyndall effect.
  • Solutions: Small particles, homogeneous, do not settle, do not scatter light.

The Tyndall Effect

The Tyndall Effect occurs when light is scattered by the dispersed particles in a colloid, making a beam of light visible. This effect helps differentiate colloids from solutions.

  • Example: A flashlight beam is visible in fog because the water droplets scatter the light.
  • Solution vs. Colloid: A laser beam passing through pure water (solution) is invisible, while in milk (colloid), the beam is scattered and visible.

Brownian Motion

Colloidal particles exhibit continuous, random movement due to collisions with molecules in the dispersing medium. This prevents them from settling.

  • Example: Pollen grains in water move in random directions when viewed under a microscope.
  • Significance: Provides evidence for the kinetic molecular theory of matter.

Examples of Colloids

  • Aerosols: Fog, smoke, mist (liquid or solid in gas).
  • Foams: Whipped cream, shaving cream (gas in liquid).
  • Emulsions: Milk, mayonnaise (liquid in liquid).
  • Gels and Sols: Gelatin, paint, blood (solid in liquid).

Questions for Students

  1. Define suspension and colloid. How do they differ?
  2. What is the Tyndall Effect? How does it help distinguish between a solution and a colloid?
  3. Explain Brownian Motion and its significance in colloids.
  4. Give three examples of colloids and identify their dispersed phase and dispersing medium.
  5. Why do colloids not settle out over time like suspensions?