Team Chemistry -
Created by: Team Chemistry -, Last Updated: July 9, 2024


A colloid is a mixture where one substance is dispersed evenly throughout another. The particles in a colloid are larger than in a solution but smaller than in a suspension. These particles do not settle out over time. An emulsion is a type of colloid where liquid droplets are dispersed in another liquid, such as milk or mayonnaise. Colloids are crucial in various industries, including food, pharmaceuticals, and cosmetics, due to their unique properties and stability.

What Is a Colloid?

A colloid is a heterogeneous mixture where one substance is dispersed evenly throughout another. The dispersed particles are larger than those in a solution but do not settle out over time, providing stability. Examples include gels, sols, and emulsions like milk.

Examples of Colloid

  1. Milk (emulsion)
  2. Mayonnaise (emulsion)
  3. Butter (emulsion)
  4. Gelatin (gel)
  5. Fog (aerosol)
  6. Smoke (aerosol)
  7. Ink (sol)
  8. Paint (sol)
  9. Whipped cream (foam)
  10. Marshmallows (foam)

Types of Colloids

  1. Sols: Sols are Solid particles dispersed in a liquid, such as ink or paint.
  2. Gels: Gels have a solid network dispersed in a liquid, like gelatin or jelly.
  3. Emulsions: Emulsions consist of liquid droplets dispersed in another liquid, like milk or mayonnaise.
  4. Foams: Foams are gas bubbles dispersed in a liquid or solid, such as whipped cream or marshmallows.
  5. Aerosols: Aerosols are tiny solid or liquid particles dispersed in a gas, like fog or smoke.
  6. Solid Sols: Solid sols have solid particles dispersed in a solid medium, such as colored glass.
  7. Liquid Aerosols: Liquid aerosols have liquid droplets dispersed in a gas, like mist or hair spray.
  8. Solid Foams: Solid foams consist of gas bubbles dispersed in a solid, like styrofoam or pumice.

Colloid Functions

  1. Food Industry: Colloids stabilize emulsions in products like mayonnaise and salad dressings.
  2. Pharmaceuticals: Colloids enhance drug delivery and absorption, such as in ointments and creams.
  3. Cosmetics: Colloids improve texture and stability in lotions and creams.
  4. Industrial Applications: Colloids are used in paints, inks, and lubricants for uniform dispersion and stability, ensuring efficient use of chemical energy in these products.
  5. Water Purification: Colloids aid in removing impurities through coagulation and flocculation processes.
  6. Medical Uses: Colloids, like blood plasma expanders, help maintain blood volume.
  7. Agriculture: Colloidal particles in fertilizers improve nutrient delivery to plants.
  8. Electronics: Colloids are used in the production of electronic components for uniform coatings.

Characteristics of Colloids

  1. Particle Size: Colloidal particles range from 1 to 1000 nanometers, larger than molecules but smaller than particles in suspensions.
  2. Tyndall Effect: Colloids scatter light when a beam passes through them, making the path of the light visible.
  3. Brownian Motion: Colloidal particles exhibit continuous, random movement due to collisions with molecules of the dispersion medium.
  4. Surface Area: Colloidal particles have a large surface area compared to their volume, enhancing their interaction with the dispersion medium.
  5. Stability: Colloidal particles do not settle out over time due to their small size and the presence of electrical charges or stabilizing agents.
  6. Adsorption: Colloidal particles can adsorb ions or molecules on their surface, affecting their stability and interaction with other substances.
  7. Charge: Colloidal particles typically carry an electric charge, leading to repulsion between particles and preventing aggregation.
  8. Viscosity: Colloidal solutions often have higher viscosity compared to the pure dispersion medium due to the dispersed particles.

Colloids Composition

Colloids consist of two main components: the dispersed phase and the dispersion medium. The dispersed phase contains tiny particles, while the dispersion medium is the substance in which these particles are distributed. Depending on their states, colloids can be classified into types such as sols, gels, emulsions, foams, and aerosols.

Preparation of Colloid Solutions

  1. Condensation Methods: These methods involve the formation of colloidal particles from smaller molecules. Techniques include chemical reactions like hydrolysis, oxidation, and reduction, which produce particles within the colloidal size range.
  2. Dispersion Methods: These methods break down larger particles into colloidal sizes. Techniques include mechanical dispersion (using colloid mills), ultrasonic treatment, and peptization, where an electrolyte stabilizes and disperses the particles.
  3. Bredig’s Arc Method: A dispersion method where an electric arc is struck between metal electrodes under water, forming metal colloids through vapor condensation.
  4. Ultrasonic Dispersion: High-frequency ultrasonic waves break down larger particles into colloidal sizes, commonly used for preparing colloidal solutions of metals and non-metals.
  5. Peptization: The process of converting a precipitate into a colloid by adding a suitable electrolyte, preventing the particles from settling.
  6. Dialysis: This purification method removes impurities from colloidal solutions by using a semipermeable membrane to separate smaller ions and molecules, maintaining the colloidal state.

Purification of Colloids

  1. Dialysis: A semipermeable membrane separates small impurities from colloidal particles, allowing only the smaller particles to pass through.
  2. Electrodialysis: An electric field speeds up dialysis by driving ions through the semipermeable membrane, enhancing purification.
  3. Ultrafiltration: A process where colloidal particles are separated from impurities using special filters with very fine pores, allowing only small molecules to pass through.
  4. Electrophoresis: Colloidal particles move towards the electrode of opposite charge under an electric field, helping to separate charged impurities.
  5. Coagulation: Adding electrolytes causes colloidal particles to clump together and settle out, leaving behind purified colloidal solution.
  6. Centrifugation: Spinning the colloidal solution at high speeds separates particles based on size and density, effectively removing impurities.

Colloid vs Solution

Particle Size1 to 1000 nanometersLess than 1 nanometer
AppearanceOften appear cloudy or opaqueClear and transparent
Tyndall EffectExhibits Tyndall effect (scatters light)Does not exhibit Tyndall effect
StabilityParticles do not settle outParticles do not settle out
Particle MovementExhibits Brownian motionMolecules move freely
Separation MethodsSeparated by centrifugation, coagulationCannot be separated by simple filtration
HomogeneityHeterogeneous at microscopic levelHomogeneous at molecular level
ExamplesMilk, fog, mayonnaiseSalt water, sugar solution

What are some common examples of colloids?

Common examples include milk, mayonnaise, fog, smoke, and whipped cream.

How are colloids different from solutions?

Colloids have larger particles that do not settle, unlike solutions with smaller, fully dissolved particles.

What is the Tyndall effect?

The Tyndall effect is the scattering of light by colloidal particles, making the light path visible.

What is Brownian motion?

Brownian motion is the random, continuous movement of colloidal particles due to collisions with molecules of the dispersion medium.

What are sols?

Sols are colloids with solid particles dispersed in a liquid, like ink or paint.

What are gels?

Gels are colloids with a solid network dispersed in a liquid, such as gelatin.

What are emulsions?

Emulsions are colloids with liquid droplets dispersed in another liquid, like milk or mayonnaise.

What are foams?

Foams are colloids with gas bubbles dispersed in a liquid or solid, such as whipped cream or styrofoam.

What are aerosols?

Aerosols are colloids with tiny solid or liquid particles dispersed in a gas, like fog or smoke.

How are colloids used in the food industry?

Colloids stabilize emulsions in products like salad dressings and mayonnaise.

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