Chemistry

• Colloids


  "Kolla" in Greek, meaning glue
• Colloids


  • Heterogeneous in nature
  • Insoluble particles of one substance are suspended in another substance
  • Dispersed phase particles are not visible but can be seen under ultramicroscope
  • Exhibits the Tyndall Effect
• For a mixture to be classified as a colloid, its suspended particles must not settle
• Colloidal State


  • Theorized by Thomas Graham (1861)
  • Observed that solutions of certain substances (sugar, salt acids and bases) diffused readily through parchment membrane while those of glue, gelatin, and silicilic acid could not
• Categories of mixtures


  • Crystalloids
  • Colloids
• True Solution


  • Solution of crystalloids in a solvent which dissolves completely
  • Transparent
• Suspension


  Some solute is visible, some solute settles down after some time
• Differences between True Solution, Colloid, Suspension

  • Visibility (microscope/eye)
  • Can pass through?
  • Type
  • Tyndall Effect
  • Electrical properties
  • Size
  • Osmotic pressure
  • Permanence
  • Effect on colligative properties
• Classification of Colloids based on Physical State

  • Foam (Gas in Liquid)
  • Solid Foam (Gas in Solid)
  • Aerosol (Liquid in Gas)
  • Emulsion (Liquid in Liquid)
  • Gel (Liquid in Solid)
  • Aerosol (Solid in Gas)
  • Sols (Solid in Liquid)
  • Solid Sols (Solid in Solid)
• There is no such thing as a gas dispersed in gas colloid
• Classification of Colloids based on Particle Attraction

  • Sols (Solid in Liquid)
  • Gels (Semisolid systems with high viscosities and solid-like rigid appearance)
  • Elastic Gels (Changes shape when force is applied, regains original shape when force is released)
  • Non-elastic Gels (Rigid)
  • Imbibition (Swelling)
  • Syneresis (Shrinking of gels in volume with time)
  • Thixotropy (Sol-gel interconversion in which some gels liquefy on shaking and change into sol but reverts to gel)
  • Emulsion (Dispersed phase and medium are both liquids)
• Conductance Method


  • Small amount of electrolyte is added to the emulsion
  • Oil-in-water = conductance increases
  • Water-in-oil = no appearance change
• Dye Test


  • Heating the emulsion with an oil-soluble dye
  • Oil-in-water = does not catch the color of the dye
  • Water-in-oil = gains the color
• Foam


  Gas in a very viscous liquid
• Hop


  A plant that gives beer its bitter taste
• Solvent Affinity


  • Lyophobic - solvent-fearing
  • Lyophilic - solvent-loving
• Adsorption


  Ability of a substance to physically hold another substance on its surface
• Brownian Motion


  Movement in a rapid, random, zigzag motion through the collision of colloidal particles in the dispersion medium
• Electrophoresis


  • Negatively-charged dispersed particles migrate to the anode
  • Positively-charged particles migrate to the cathode
• Gold Number


  Number referred to as the protective power of lyophilic colloid
• The egg albumin is a very good emulsifying agent