Surface Chemistry - Examples of Colloids

  • Definition of colloids
  • Classification of colloids
    • Based on the nature of dispersion medium
    • Based on the nature of dispersed phase
  • Characteristics of colloidal solutions
  • Difference between true solutions, colloids, and suspensions
  • Examples of colloids
    • Solid-liquid colloids
      • Milk
      • Blood
    • Liquid-liquid colloids
      • Emulsions (e.g., mayonnaise)
    • Gas-liquid colloids
      • Foam (e.g., whipped cream)
    • Gas-solid colloids
      • Smoke
    • Liquid-solid colloids
      • Paint

Surface Chemistry - Tyndall Effect

  • Definition and explanation of the Tyndall effect
    • Scattering of light in colloidal solutions
  • Phenomenon behind the Tyndall effect
    • Particles in the dispersed phase being of sizes comparable to the wavelength of light
  • Examples of the Tyndall effect in everyday life
    • Sunbeams passing through a dusty room
    • Headlights penetrating fog
  • Applications of the Tyndall effect
    • Determination of particle size in colloidal solutions
    • Detecting the presence of colloids in solutions

Surface Chemistry - Brownian Motion

  • Explanation of Brownian motion
    • Random motion of colloidal particles in a dispersed medium
  • Cause of Brownian motion
    • Constant collision between the particles and the molecules of the dispersion medium
  • Importance of Brownian motion
    • Preventing the settling down of colloidal particles
  • Application of Brownian motion
    • Measurement of Avogadro’s number

Surface Chemistry - Preparation of Colloids

  • Methods of preparing colloidal solutions
    • Dispersion method
    • Condensation method
    • Mechanical dispersion method
    • Electrodispersion method
    • Chemical method
  • Examples of preparation methods
    • Dispersion method: Grinding solid in liquid
    • Condensation method: Chemical reaction between two substances
    • Mechanical dispersion method: Expelling a liquid through a fine hole
    • Electrodispersion method: Passing an electric current through an electrolyte
    • Chemical method: Precipitation method or double decomposition method

Surface Chemistry - Purification of Colloids

  • Importance of purifying colloidal solutions
  • Methods of purifying colloidal solutions
    • Dialysis
      • Principle of dialysis
      • Dialysis tube setup
    • Ultrafiltration
      • Using a membrane with small pores

Surface Chemistry - Peptization

  • Definition of peptization
  • Mechanism of peptization
    • Addition of a suitable electrolyte
    • Neutralization of the charge on the colloidal particles
  • Examples of peptization
    • Addition of a small amount of ferric chloride to precipitated ferric hydroxide
    • Formation of colloidal sols of gold or sulfur by shaking with water in the presence of small amounts of nitric acid

Surface Chemistry - Emulsion

  • Definition of emulsion
  • Types of emulsions
    • Oil-in-water (O/W) emulsion
    • Water-in-oil (W/O) emulsion
  • Factors affecting emulsion stability
    • Interfacial tension
    • Particle size distribution
    • Electric charge on the dispersed phase
    • Viscosity of the dispersion medium
  • Examples of emulsions
    • Mayonnaise (O/W emulsion)
    • Butter (W/O emulsion)

Surface Chemistry - Adsorption

  • Definition of adsorption
  • Difference between adsorption and absorption
  • Types of adsorption
    • Physical adsorption (physisorption)
      • Weak forces of attraction
    • Chemical adsorption (chemisorption)
      • Formation of chemical bonds
  • Factors affecting adsorption
    • Nature of adsorbate and adsorbent
    • Temperature
    • Pressure
  • Examples of adsorption
    • Adsorption of a gas by activated charcoal
    • Adsorption of dyes by fabrics

Surface Chemistry - Factors Affecting Adsorption

  • Effect of temperature on adsorption
    • Physisorption: Decreased adsorption with increasing temperature
    • Chemisorption: Increased adsorption with increasing temperature
  • Effect of pressure on adsorption
    • Physisorption: Increased adsorption with increasing pressure
    • Chemisorption: Pressure has little effect on adsorption
  • Role of activation energy
  • Effect of nature of adsorbate and adsorbent
    • Choice of adsorbent with high surface area
    • Adsorbate with correct polarity

Surface Chemistry - Examples of Colloids

  • Solid-liquid colloids
    • Milk
      • Casein proteins dispersed in water
    • Blood
      • Red and white blood cells dispersed in plasma
  • Liquid-liquid colloids
    • Emulsions
      • Mayonnaise: Oil droplets dispersed in vinegar and egg yolk
  • Gas-liquid colloids
    • Foam
      • Whipped cream: Air bubbles dispersed in cream
  • Gas-solid colloids
    • Smoke
      • Solid particles dispersed in air
  • Liquid-solid colloids
    • Paint
      • Pigment particles dispersed in a liquid medium

Slide 21:

Surface Chemistry - Examples of Colloids

  • Solid-liquid colloids
    • Milk: Casein proteins dispersed in water
    • Blood: Red and white blood cells dispersed in plasma
  • Liquid-liquid colloids
    • Emulsions
      • Mayonnaise: Oil droplets dispersed in vinegar and egg yolk
  • Gas-liquid colloids
    • Foam
      • Whipped cream: Air bubbles dispersed in cream Slide 22:

Surface Chemistry - Examples of Colloids (continued)

  • Gas-solid colloids
    • Smoke: Solid particles dispersed in air
  • Liquid-solid colloids
    • Paint: Pigment particles dispersed in a liquid medium
  • Other examples of colloidal solutions
    • Ink: Pigment particles dispersed in a liquid medium
    • Rubber: Polymer chains dispersed in a liquid medium Slide 23:

Surface Chemistry - Preparation of Sol

  • What is a sol?
    • A colloidal dispersion of solid particles in a liquid medium
    • The liquid medium is often water
  • Methods of preparing sols
    • Disintegration method: Breaking down larger particles into smaller particles
    • Dispersion method: Breaking down larger particles with the help of a dispersing medium
    • Condensation method: Chemical reaction between substances to form colloids Slide 24:

Surface Chemistry - Preparation of Sol (continued)

  • Example of disintegration method
    • Grinding: Reducing the size of solid particles by grinding them in a solvent
  • Example of dispersion method
    • Shaking: Agitating a solid in a liquid medium to break it down into smaller particles
  • Example of condensation method
    • Chemical reaction: Mixing two or more substances to form colloidal particles
    • e.g., Formation of silver chloride sol by mixing silver nitrate and sodium chloride Slide 25:

Surface Chemistry - Properties of Sol

  • Particle size in sols
    • The particles in sols have sizes in the range of 1 nm to 1000 nm
  • Suspension stability
    • Sols are stable suspensions where the dispersed particles do not settle down over time
  • Optical properties
    • Many sols exhibit the Tyndall effect, where they scatter light, making the beam visible Slide 26:

Surface Chemistry - Properties of Sol (continued)

  • Colligative properties
    • Sols show colligative properties like lowering of vapor pressure, elevation in boiling point, depression in freezing point, and osmotic pressure
  • Stability of sols
    • Sols can be stabilized by adding electrolytes or surfactants
  • Coagulation of sols
    • The destabilization and clumping together of colloidal particles, leading to the formation of a precipitate Slide 27:

Surface Chemistry - Applications of Colloids

  • Industrial applications of colloids
    • Stabilizing agents: Colloids are used to stabilize emulsions and foams in industries like food, cosmetics, and pharmaceuticals
    • Catalysts: Some colloidal solutions act as catalysts in chemical reactions, enhancing reaction rates
  • Biological relevance of colloids
    • Colloidal solutions play vital roles in various biological processes, such as digestion, cell functioning, and immune responses Slide 28:

Surface Chemistry - Applications of Colloids (continued)

  • Medical applications of colloids
    • Drug delivery: Colloidal systems are used to deliver drugs to specific targets in the body
    • Diagnostic tools: Colloidal gold nanoparticles are used in medical diagnostics, such as pregnancy tests and lateral flow assays
  • Environmental applications of colloids
    • Wastewater treatment: Colloidal particles can be used to remove pollutants from wastewater through adsorption and coagulation processes Slide 29:

Surface Chemistry - Summary

  • Colloidal solutions are heterogeneous mixtures with particle sizes ranging from 1 nm to 1000 nm
  • Various types of colloids include solid-liquid, liquid-liquid, gas-liquid, gas-solid, and liquid-solid colloids
  • Colloids can be prepared through dispersion, condensation, and disintegration methods
  • Sol properties include particle size, suspension stability, optical properties, colligative properties, stability, and coagulation
  • Colloids find applications in various industries, biology, medicine, and environmental processes Slide 30:

Surface Chemistry - Recap

  • What are colloids? How are they different from suspensions and solutions?
  • Give examples of different types of colloidal solutions.
  • How can colloidal sols be prepared using different methods?
  • What are the properties of colloidal sols?
  • What are some applications of colloids in industries, biology, medicine, and the environment?