Summative Test 2 Review

• Colloidal particles


  All carry the same type of charge
• Dispersion medium


  Has equal opposite charge
• Electrophoresis


  1. Movement of colloidal particles towards a particular electrode under the influence of an electrical field

  2. Used to find the nature of charge carried by colloidal particles in a colloidal dispersion

  3. Colloidal particles carry a particular type of charge
• Applications of electrophoresis


  • Removal of dirt particles
  • Electro-deposition of rubber
• Electro-osmosis


  1. Movement of dispersion medium under the influence of an electrical field

  2. Movement of colloidal particles is prevented with the help of a suitable membrane
• Adsorption


  • Concentration of gas, liquid, or solid on the surface of colloidal particles it's in contact with
  • One of the most important characteristics of colloids due to its tremendous surface area
• Condensation Method


  1. Smaller to larger (excessive cooling)

  2. Substances which are more soluble in one solvent as compared to the other

  3. Can be obtained by pouring the solution of substance in which it is more soluble than the other solvent
• Substances more soluble in alcohol than water


  • Sulphur
  • Phosphorus
• Substances more soluble in alcohol than water

  • Phenolphthalein
• Dispersion Method


  Larger to smaller (heating and stirring)
• Peptization


  1. Redispersion of coagulated sol

  2. Dispersion of coagulated mass in which colloidal particles pre-exist

  3. Heating and stirring
• Bredig's Arc Method


  1. Rubbing two metal electrodes beneath the surface of a liquid containing the suspended particles

  2. Particles soon begin to disperse finely in liquid
• Protective Colloids


  Hydrophobic sols acquiring greater stability towards coagulation in the presence of certain lyophilic sols
• Protection


  Process of protecting a lyophobic sol from being coagulated on addition of an electrolyte using lyophilic colloids
• Gold Number


  • Number referred to as the protective power of lyophilic colloid
  • Smaller value, greater protective power
• Protective Colloids and their Gold Numbers


  • Gelatin (0.005-0.01)
  • Casein (0.01-0.02)
  • Hemoglobin (0.03-0.07)
  • Egg Albumin (0.08–0.10)
  • Gum Arabic (0.10-0.15)
  • Dextrin (6-20)
  • Starch (20-25)
• Methods to break colloids


  • Physical methods (centrifuging, filtration, lowering viscosity, etc.)
  • Chemical methods (addition of oppositely charged colloids to decrease negative charge of dispersed phase, dehydration of emulsifying agent, chemical reaction with emulsifier to alter efficiency or "salting out")
• Dialysis


  Removing dissolved electrolytes from the sol by membrane
• Ultrafiltration


  Separation of colloidal particles from solution by filtration through an ultrafilter
• Filtration


  Removal of suspended colloidal particles from liquid by passing through a porous medium
• Common colloids


  • Mayonnaise (oil-in-water, lecithin as emulsifying agent)
  • Jellies (gel that belongs to the sol type of colloidal dispersion, pectin (carbohydrate) responsible for entangled mass)
  • Gelatin (collagen as raw material, best aids to weight control, 3-ounces (85 g) of flavored gelatin can supply 37% of protein need of adults)
• Brownian Motion


  Irregular movement of dispersed particles caused by the impact of fast-moving molecules of the liquid medium/solvent against the particles
• Brownian Motion


  • Size of particles is inversely proportional to the speed of motion
  • Transfer of momentum is inversely proportional to the mass
  • Lighter particles = greater speeds from collisions
  • Speed is inversely proportional to viscosity
• Viscosity


  • Quantity that expresses the magnitude of the internal friction in a liquid
  • Fluid's resistance to flow
• Effects of Brownian Motion


  • Particles in a fluid are constantly moving
  • Leads to stability of colloidal solutions
  • Albert Einstein's proof of the existence of atoms and molecules
• Diffusion


  1. Graham's Law - rate of diffusion decreases very quickly with the increase in the mass size of particles

  2. Colloidal solutions diffuse more slowly than ordinary molecular solutions
• Rate of Setting / Sedimentation of Suspensions


  • In colloidal systems, very dense dispersed particles do not sink but may remain suspended for some time
  • Colloids' rate of setting depends on the influence of gravity
• Examples of rate of setting

  • Clay in water - 7 minutes
  • Carbon-water colloid - no noticeable change in 20 years
• Tyndall Effect


  • Amount of scattering depends on light's frequency and density of particles
  • Zone of scattered light is larger than the particle itself
  • Colloidal particles look like bright spots at right angles to the beam of light (under a microscope)
• Tyndall Cone


  Illuminated path produced by Tyndall Effect
• Ultramicroscope


  Used by Richard Adolf Zsigmondy to show the heterogeneous structure of colloids
• Brownian Motion is the movement of dispersed particles caused by the impact of fast-moving molecules of liquid medium or solvent against the particles.