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
- Solid-liquid colloids
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
- Dialysis
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
- Physical adsorption (physisorption)
- 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
- Milk
- Liquid-liquid colloids
- Emulsions
- Mayonnaise: Oil droplets dispersed in vinegar and egg yolk
- Emulsions
- Gas-liquid colloids
- Foam
- Whipped cream: Air bubbles dispersed in cream
- Foam
- Gas-solid colloids
- Smoke
- Solid particles dispersed in air
- Smoke
- Liquid-solid colloids
- Paint
- Pigment particles dispersed in a liquid medium
- Paint
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
- Emulsions
- Gas-liquid colloids
- Foam
- Whipped cream: Air bubbles dispersed in cream Slide 22:
- Foam
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?
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