Koloid | Kimia SMA

Scientific concepts & nature phenomena presented

1) Colloids in nature (fog and clouds)

• Morning fog / clouds occur because water droplets are dispersed in air.
• Fog/clouds are described as colloids (a mixture type).

2) Definition and particle-size range

• A mixture is called a colloid when the particle (dispersed) size is ~1–100 nanometers.
• Colloids are positioned between:
  • Solutions (smaller particles)
  • Suspensions (larger particles)
• Although colloids may look homogeneous/uniform, they are heterogeneous internally.

3) Two-phase structure of colloids (as described)

• Dispersed phase: the particles distributed throughout the mixture.
• Dispersing medium: the material the particles are distributed in.

4) Types of colloids (by phase combination)

Note: Some subtitle wording is inconsistent in places, but the main phase-based classification is reflected below.

• Solid sol: solid dispersed phase in solid medium
  • Examples: colored glass, diamonds
• Liquid sol: liquid dispersed phase in solid/solid context (per subtitle)
  • Examples given: gold sols, ink
• Solid emulsion: liquid dispersed phase in solid medium
  • Examples: jelly, pearls
• Liquid emulsion: both dispersed phase and medium are liquid
  • Examples: coconut milk, milk solid foam (as stated)
• Liquid foam: gas dispersed in liquid
  • Examples: soap foam, whipped cream
• Solid aerosol: solid dispersed in gas
  • Example: smoke
• Liquid aerosol: liquid dispersed in gas
  • Example: fog

5) Key properties of colloids

• Tyndall effect:
  • Light scattering by colloidal particles (e.g., dust), making a light beam appear clearer in dusty rooms.
• Brownian motion / Brownian friction (random motion):
  • Random movement of colloidal particles caused by collisions, helping colloids stay stable and not settle.
• Absorption (adsorption by surface of colloidal particles):
  • Example: activated charcoal absorbing odor-causing molecules.
• Coagulation (clumping):
  • Caused by adding electrolytes or changing temperature.
  • Example use: water purification with alum, where alum binds pollutants and they settle.
• Dialysis:
  • Separation/purification of colloids from interfering ions using a semi-permeable membrane.
  • Example use: blood washing/dialysis in kidney failure patients.
• Electrophoresis:
  • Separation of charged colloidal particles under an electric current.
  • Example use: dust filtering in factory chimneys.

6) Stabilizers and common additives

• Protective colloids (also called protective substances in subtitle):
  • Cover colloid particles, reducing attractive forces and preventing clumping.
  • Example: gelatin in ice cream.
• Emulsifiers (emulsion stabilizers):
  • Prevent separation of oil and water phases.
  • Example: lecithin (from egg yolks), used in mayonnaise to keep oil and water from separating.

7) Leophilic vs lyophobic colloids (interaction-based classification)

• Leophilic (lyophilic) colloids: dispersed particles attract the dispersing medium
  • Examples given: soap? (subtitle later lists soap, agar-agar, starch, detergent as examples of lyophilic—wording is inconsistent, but concept is clear)
  • Properties: thicker, more stable, harder to precipitate, reversible (can reform after settling)
• Lyophobic colloids: dispersed particles do not attract the dispersing medium
  • Examples given: sulfur sol vs metal sol; iron hydroxide sol (as stated)
  • Properties: more difficult to remain stable without intervention, irreversible precipitation behavior

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Methods to produce colloids (outlined)

• Two general methods:
  1. Dispersion method
     • Break large particles into colloidal sizes
     • Can be done:
       • Mechanically (subtitle: “petization / mechanical breik arc”)
         • Grinding/pounding and mixing with a dispersing medium
         • Example: make sulfur sol by grinding sulfur powder with granulated sugar, then adding hot water.
       • Peptization
         • Add a breaking agent / peptizer to a precipitate to form a colloid
         • Example: adding KOH solution to an aluminum hydroxide precipitate to form aluminum hydroxide sol
       • Electric-current vapor dispersion (subtitle’s continuation of “breik arc”)
         • A strong electric current forms metal vapor that disperses in a liquid (e.g., water)
         • Example target colloids: gold sol, platinum sol
  2. Condensation method
     • Combine small particles into colloidal-sized particles
     • Usually done via chemical reactions
     • Example: make gold sol by reacting gold(III) chloride solution with a reducing agent like formaldehyde, producing colloidal gold particles

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Applications mentioned

• Coagulating latex to produce rubber
• Clean water treatment
• Manufacturing medicines, vaccines, and cosmetics

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Researchers or sources featured

• No specific researchers, scientists, or external sources are named in the provided subtitles.