Colloidal Solutions and Suspensions

Suspensions

• Definition and Stability:

  • A suspension is an unstable mixture containing particle sizes larger than those in solutions or colloids.
  • Examples of Suspensions:
  • Sand in water ($H_2O$)
  • Oil in water
  • Muddy water
  • Chalk in water ($H_2O$)

• Behavior Under Different Physical Conditions:

  • Disturbed Condition:
  • Solute/suspended particles do not settle down.
  • Displays the Tyndall Effect (scatters light passing through it).
  • Undisturbed Condition:
  • Suspended particles settle down at the bottom under gravity.
  • Settle down causes the suspension to break.
  • Does not show the Tyndall Effect once particles have settled.

Colloidal Solutions

• Particle Size Range:

  • Particle size ($S_{ne}$) ranges from $1\,nm$ to $100\,nm$.
  • This size lies intermediate between a true solution (particle size < $1\,nm$) and a suspension (particle size > $100\,nm$).

• Physical Properties & Appearance:

  • Solute particles in a colloidal solution cannot be seen through naked eyes.
  • Due to their fine size, colloidal solutions appear to be homogeneous to the naked eye, but in actual reality, they are heterogeneous mixtures.
  • Colloidal solutions are inherently stable systems (particles remain distributed and do not settle out naturally).

• Optical Behavior:

  • Colloids show the Tyndall Effect when a beam of light passes through the mixture, scattering light and making the beam's path visible.

Components of Colloidal Solutions

• A colloidal system is comprised of two essential parts, analogous to solute and solvent:

  • Dispersed Phase:
  • Corresponds to the solute.
  • Present in a smaller quantity (less quantity).
  • Dispersing Medium:
  • Corresponds to the solvent.
  • Present in a larger quantity (large quantity).

• Concrete Example (Milk):

  • Dispersed Phase (Solute): Oil / fats
  • Dispersing Medium (Solvent): Water ($H_2O$)

Types and Classification of Colloidal Solutions

• Summary Classification Table:

  • Fog, Mist:

  • Colloidal Type: Aerosol

  • Dispersion Medium: Liquid

  • Dispersed Phase: Gas

  • Smoke, Exhaust:

  • Colloidal Type: Aerosol

  • Dispersion Medium: Solid

  • Dispersed Phase: Gas

  • Milk, Vanishing Cream (Oil in Water):

  • Colloidal Type: Emulsion

  • Dispersion Medium: Liquid (oil)

  • Dispersed Phase: Liquid (water)

  • Cold Cream, Butter (Water in Oil):

  • Colloidal Type: Emulsion

  • Dispersion Medium: Liquid (water)

  • Dispersed Phase: Liquid (oil)