Introduction to Colloidal Dispersions
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Questions and Answers

What is the relationship between specific viscosity and volume fraction in colloids?

  • Specific viscosity is proportional to the square of the volume fraction.
  • Specific viscosity is inversely proportional to the volume fraction.
  • Specific viscosity is equal to 2.5 times the volume fraction. (correct)
  • Specific viscosity is constant regardless of volume fraction.

    • Which statement accurately describes the effect of particle shape on the viscosity of colloidal solutions?

  • Spherical colloid particles lead to a higher viscosity than linear particles. (correct)
  • Shape affects viscosity only in non-colloidal dispersions.
  • Viscosity is independent of the shape of the colloidal particles.
  • Linear colloid particles exhibit lower viscosity than spherical particles.

    • What best describes the stability of lyophilic colloids compared to lyophobic colloids?

  • Lyophilic colloids are more stable due to strong attraction with the dispersion medium. (correct)
  • Both types are equally stable as they both precipitate easily.
  • Lyophilic colloids are less stable due to high coagulation rates.
  • Lyophilic colloids are unstable but can easily reform after separation.

    • What role does electrical charge play in the stability of colloidal dispersions?

    <p>Mutual repulsion between similarly charged particles prevents aggregation.</p> Signup and view all the answers

    Which characteristic is NOT associated with lyophilic colloids?

    <p>Irreversible nature after separation.</p> Signup and view all the answers

    How does ionization contribute to the electrical charge of colloidal particles?

    <p>Ionization of surface groupings alters the surface charge of particles.</p> Signup and view all the answers

    What term best describes colloids that have no affinity for the dispersion medium?

    <p>Lyophobic colloids.</p> Signup and view all the answers

    Which of the following mechanisms does NOT contribute to the charging of interfaces in colloidal systems?

    <p>Thermal decomposition</p> Signup and view all the answers

    Which of the following would be considered a lyophobic colloid?

    <p>Sols of silver or gold.</p> Signup and view all the answers

    Which statement is true regarding lyophobic colloids?

    <p>They are inherently unstable and can coagulate.</p> Signup and view all the answers

    What is a key characteristic of the dispersed phase in lyophilic colloids?

    <p>It is surrounded by a layer of solvent and charged particles.</p> Signup and view all the answers

    How do lyophilic colloids compare to lyophobic colloids in biological systems?

    <p>Lyophilic colloids are more frequently encountered in biological systems.</p> Signup and view all the answers

    Which mechanism leads to the formation of lyophilic colloids?

    <p>Spontaneous tendency of dispersed phase to integrate with the medium.</p> Signup and view all the answers

    What does osmotic pressure primarily influence in a colloidal solution?

    <p>The retention of fluid within a blood vessel</p> Signup and view all the answers

    Which equation is used for determining the molecular weight of colloids in dilute solution?

    <p>Van’t Hoff equation</p> Signup and view all the answers

    How does the shape of linear colloidal particles affect viscosity in a dispersion?

    <p>It decreases viscosity when the particles coil into spheres</p> Signup and view all the answers

    What is the primary purpose of measuring viscosity in colloidal dispersions?

    <p>To derive information about the molecular weight and shape of particles</p> Signup and view all the answers

    In the Van't Hoff equation, what does the variable 'R' represent?

    <p>Molar gas constant</p> Signup and view all the answers

    What effect does a solute have on osmotic pressure in a solution?

    <p>Increases osmotic pressure by introducing solute particles</p> Signup and view all the answers

    Which of the following statements about crystalloid solutions is accurate?

    <p>They consist of sugar or salt mixtures in water</p> Signup and view all the answers

    What does the variable 'φ' represent in Einstein's equation for viscosity?

    <p>Volume fraction of dispersion</p> Signup and view all the answers

    What is the primary purpose of adding a stabilizer during the preparation of lyophobic colloids?

    <p>To enhance the stability of the sol produced</p> Signup and view all the answers

    Which mechanical dispersion method involves the use of a rotating vessel with metal balls?

    <p>Ball mill</p> Signup and view all the answers

    What is the term for converting freshly prepared precipitate into colloidal form using an electrolyte?

    <p>Peptization</p> Signup and view all the answers

    In a colloid mill setup, which configuration allows for the disintegration of solid particles?

    <p>One fixed and one rotating plate</p> Signup and view all the answers

    Which method employs high-speed rotation to achieve particle dispersion?

    <p>Mechanical disintegration</p> Signup and view all the answers

    What causes peptization to occur when an electrolyte is added to a precipitate?

    <p>Adsorption of electrolyte ions by precipitate particles</p> Signup and view all the answers

    What happens to the stability of lyophobic colloids when suitable stabilizers are not added?

    <p>They will aggregate and settle</p> Signup and view all the answers

    What role do ultrasonic waves play in the preparation of lyophobic colloids?

    <p>They facilitate mechanical dispersion of particles</p> Signup and view all the answers

    What type of colloidal solution can be obtained by excessive cooling in an organic solvent?

    <p>Colloidal solution of ice</p> Signup and view all the answers

    Which process involves passing hot vapor through water to condense vapor into a precipitate?

    <p>Thermal condensation</p> Signup and view all the answers

    What distinguishes lyophilic colloids from lyophobic colloids?

    <p>Lyophilic colloids have a higher viscosity than the dispersing medium.</p> Signup and view all the answers

    What is a common property of lyophobic colloids?

    <p>Exhibit Tyndall effect</p> Signup and view all the answers

    When a true solution is mixed with an excess of another solvent, what type of solution is typically formed?

    <p>Colloidal solution of the solute</p> Signup and view all the answers

    What will happen when a concentrated solution is poured into a liquid in which the solute is insoluble?

    <p>Precipitation due to saturation</p> Signup and view all the answers

    In the comparison of colloids, what is true about association colloids?

    <p>They are thermodynamically unstable.</p> Signup and view all the answers

    What is a characteristic of lyophobic colloids when electrolytes are added?

    <p>They precipitate at low electrolyte concentration.</p> Signup and view all the answers

    What is the primary effect of increasing the valency of an effective ion in a colloidal system?

    <p>It increases the precipitation power.</p> Signup and view all the answers

    Which process describes the separation of a colloid-rich layer from a lyophilic sol?

    <p>Coacervation</p> Signup and view all the answers

    What occurs during complex coacervation?

    <p>Mixing of oppositely charged lyophilic colloids.</p> Signup and view all the answers

    What is the role of hydrophilic colloids in sensitization?

    <p>They trigger coagulation in opposite charged colloids.</p> Signup and view all the answers

    What is one method of microencapsulation derived from coacervation?

    <p>Surrounding solid particles with macromolecular materials.</p> Signup and view all the answers

    How do hydrophilic colloids affect the stability of hydrophobic colloids in the presence of electrolytes?

    <p>They enhance stability against electrolytic precipitation.</p> Signup and view all the answers

    What is the result of boiling a sol such as silver halides dispersed in water?

    <p>It causes coagulation of the sol particles.</p> Signup and view all the answers

    Which type of ions are involved in the reaction that leads to coacervation?

    <p>Ions of opposite charges.</p> Signup and view all the answers

    Which method is used to measure the turbidity of a solution?

    <p>Spectrophotometer</p> Signup and view all the answers

    What is the primary characteristic of Brownian motion observed in colloidal particles?

    <p>Erratic, random zigzag movement</p> Signup and view all the answers

    What happens to Brownian motion as the viscosity of the dispersion medium increases?

    <p>It decreases and may eventually stop</p> Signup and view all the answers

    How is turbidity mathematically expressed in relation to molecular weight?

    <p>Hc / T = 1/M + 2Bc</p> Signup and view all the answers

    What effect does the size of a colloidal particle have on Brownian motion?

    <p>Brownian motion decreases with an increase in particle size</p> Signup and view all the answers

    Which particle shapes have been identified in colloids?

    <p>Spheroid, rod-like, and disc-like</p> Signup and view all the answers

    Which equipment is suitable for measuring turbidity in a colloidal solution?

    <p>Nephelometer</p> Signup and view all the answers

    What does the term 'turbidity' refer to in a colloidal system?

    <p>The concentration of dispersed particles</p> Signup and view all the answers

    What primarily influences the erythrocyte sedimentation rate (ESR)?

    <p>The concentration of fibrinogen and zeta potential</p> Signup and view all the answers

    Under which conditions is the erythrocyte sedimentation rate generally elevated?

    <p>Pregnancy and inflammatory processes</p> Signup and view all the answers

    Which factor does NOT contribute to the sedimentation of red blood cells?

    <p>Temperature of the test environment</p> Signup and view all the answers

    What charge do silver iodide particles acquire when there is an excess of silver ions in the reaction mixture?

    <p>Positive charge</p> Signup and view all the answers

    How does osmotic pressure relate to molecular weight according to Van't Hoff's law?

    <p>Osmotic pressure decreases as molecular weight increases</p> Signup and view all the answers

    What defines the combination of a positively charged surface and surrounding counter ions in colloids?

    <p>Stern Double Layer</p> Signup and view all the answers

    What is the main characteristic of the internal solution in osmosis?

    <p>It contains non-penetrating ions of colloidal dimensions</p> Signup and view all the answers

    What does the Tyndall effect demonstrate in colloidal solutions?

    <p>Light scattering properties of colloidal particles</p> Signup and view all the answers

    Which ions are considered potential determining ions for metal oxides and hydroxides?

    <p>H+ and OH-</p> Signup and view all the answers

    What happens to red blood cells during inflammation that influences their sedimentation rate?

    <p>They aggregate to form rouleaux</p> Signup and view all the answers

    Which statement is true regarding the application of centrifugal force in studying micellar properties?

    <p>It applies a force of up to 4 x 10^5g</p> Signup and view all the answers

    What is the primary function of the Ultramicroscope?

    <p>To detect the size of individual colloidal particles using light scattering</p> Signup and view all the answers

    What results from the selective adsorption of ions around a colloidal particle?

    <p>Charging of the particle surface</p> Signup and view all the answers

    Which factor influences the color of a hydrophobic sol?

    <p>The particle size and wavelength of light scattered</p> Signup and view all the answers

    What is the difference in potential between the compact layer and the bulk of the solution known as?

    <p>Zeta potential</p> Signup and view all the answers

    Why is there a practical lower limit of about 1 micron in sedimentation studies under gravity?

    <p>Data becomes unreliable due to Brownian motion</p> Signup and view all the answers

    When excess iodide ions are present during the reaction of silver iodide formation, what charge do the AgI particles acquire?

    <p>Negative charge</p> Signup and view all the answers

    Which of the following statements about the particle size of colloids is accurate?

    <p>Colloidal particles range from 1 nm to 1 um in size.</p> Signup and view all the answers

    How do larger colloidal particles interact with light compared to smaller particles?

    <p>They transmit shorter wavelengths and absorb longer wavelengths.</p> Signup and view all the answers

    What type of layer consists of the fixed charges on the particle surface and counter ions in the surrounding medium?

    <p>Stern layer</p> Signup and view all the answers

    What is a distinguishing feature of true solutions in relation to light scattering?

    <p>They do not scatter light due to small particle size.</p> Signup and view all the answers

    What is the effect of increasing the concentration of either type of potential determining ion in the double layer?

    <p>Altered particle charge</p> Signup and view all the answers

    What does the term 'Tyndall cone' refer to in colloidal chemistry?

    <p>The illuminated path of light due to scattering by colloidal particles.</p> Signup and view all the answers

    Which instrument is used to observe individual sol particles at high magnification?

    <p>Electron microscope</p> Signup and view all the answers

    What is the main purpose of protective colloids in relation to hydrophobic colloids?

    <p>To prevent precipitation upon adding an electrolyte.</p> Signup and view all the answers

    Which of the following is a disadvantage of colloidal preparations?

    <p>Stabilization of lyophobic colloids can be challenging.</p> Signup and view all the answers

    What is a significant advantage of colloidal preparations in pharmaceuticals?

    <p>Colloidal preparations can enhance the taste of medications.</p> Signup and view all the answers

    What is one reason for the use of colloidal gold in medicine?

    <p>It is non-toxic and can carry drugs and antibiotics.</p> Signup and view all the answers

    What challenge is associated with the preparation of lyophobic colloids?

    <p>They can be destabilized by several environmental factors.</p> Signup and view all the answers

    How do colloids contribute to the dispersion of insoluble materials?

    <p>They facilitate easier absorption and distribution.</p> Signup and view all the answers

    What drawback is associated with ionic silver salt in biological systems?

    <p>The formation of insoluble silver chloride limits its usefulness.</p> Signup and view all the answers

    What are colloidal preparations commonly used for in the paint industry?

    <p>To provide good coverage and adhesion.</p> Signup and view all the answers

    What characteristic primarily distinguishes lyophilic colloids from lyophobic colloids?

    <p>Lyophilic colloids have a strong affinity for the dispersion medium, while lyophobic colloids do not.</p> Signup and view all the answers

    Which of the following statements accurately describes the stability of lyophobic colloids?

    <p>They eventually coagulate and are irreversible.</p> Signup and view all the answers

    What process is reflected in the spontaneous formation of lyophilic colloids when combined with a dispersion medium?

    <p>Affinity and attraction between disperse phase and medium.</p> Signup and view all the answers

    What type of colloidal particles are characterized by having no affinity for the dispersion medium?

    <p>Lyophobic colloids</p> Signup and view all the answers

    Which example accurately represents a hydrophobic colloid?

    <p>Sol of gold</p> Signup and view all the answers

    What is the nature of the stability factors surrounding a solute particle in lyophilic colloids?

    <p>Layer of solvent and electrical charges.</p> Signup and view all the answers

    Which statement best characterizes lyophilic colloids in biological systems?

    <p>They are often involved in cellular processes and hydration.</p> Signup and view all the answers

    What happens when the dispersion medium is removed from lyophilic colloids?

    <p>The sol can be easily reconstituted by adding the medium back.</p> Signup and view all the answers

    Which of the following best describes the nature of association colloids?

    <p>Exhibit a dual affinity for both the solvent and dispersed phase.</p> Signup and view all the answers

    What is the defining property of macromolecular colloids?

    <p>Their particles are large, typically over 100 nm in size.</p> Signup and view all the answers

    In sol systems where water is the dispersion medium, what term is used to describe the system?

    <p>Hydrosol</p> Signup and view all the answers

    How does the rigidity of a gel arise?

    <p>Through the intertwining network that traps the dispersion medium.</p> Signup and view all the answers

    Which of the following is characteristic of lyophobic colloids?

    <p>They are generally less stable without suitable stabilizers.</p> Signup and view all the answers

    What is the primary interaction that holds multimolecular colloids together?

    <p>Weak van der Waals forces among particle aggregates.</p> Signup and view all the answers

    What type of dispersion medium is used in the formation of foams?

    <p>Liquid</p> Signup and view all the answers

    Which example best represents an aerosol in colloidal systems?

    <p>Smoke</p> Signup and view all the answers

    What best describes lyophobic colloids?

    <p>They coagulate quickly in the absence of stabilizers.</p> Signup and view all the answers

    Which statement accurately differentiates lyophilic colloids from lyophobic colloids?

    <p>Lyophilic colloids are more stable than lyophobic colloids.</p> Signup and view all the answers

    What characteristic of lyophilic colloids allows them to be unstable in certain conditions?

    <p>Their ability to form gel-like structures.</p> Signup and view all the answers

    Which of the following substances is an example of a lyophilic colloid?

    <p>Methylcellulose</p> Signup and view all the answers

    What is a fundamental property of lyophobic colloids that distinguishes them from lyophilic colloids?

    <p>They rapidly coagulate when external conditions change.</p> Signup and view all the answers

    How do lyophilic colloids behave when the dispersion medium is removed?

    <p>They can be reconstituted by remixing.</p> Signup and view all the answers

    Why are lyophobic colloids referred to as extrinsic colloids?

    <p>Due to their lack of affinity for the dispersion medium.</p> Signup and view all the answers

    What mechanism leads to the stability of lyophilic colloids in a dispersion medium?

    <p>The presence of a layer of solvent and electrical charge.</p> Signup and view all the answers

    What primarily determines the osmotic pressure in a colloidal solution?

    <p>The concentration of solute particles</p> Signup and view all the answers

    What characteristic of linear colloidal dispersions affects their viscosity?

    <p>Their tendency to coil into spheroidal shapes</p> Signup and view all the answers

    Which equation is specifically used to relate osmotic pressure to the molecular weight of colloids?

    <p>Van't Hoff equation</p> Signup and view all the answers

    How does the viscosity of a colloidal dispersion change with respect to its volume fraction?

    <p>Viscosity changes quadratically with volume fraction</p> Signup and view all the answers

    What key property does osmotic pressure NOT influence in a colloidal system?

    <p>Energy yield from metabolic processes</p> Signup and view all the answers

    In the context of viscosities, what does the variable $η_o$ represent in Einstein's equation?

    <p>The viscosity of the surrounding medium</p> Signup and view all the answers

    What is the primary function of viscosity measurements in colloidal dispersions?

    <p>To calculate the molecular weight and shape of particles</p> Signup and view all the answers

    Which component in the Van't Hoff equation does not contribute directly to osmotic pressure?

    <p>Concentration of solute particles (c)</p> Signup and view all the answers

    What happens to the surface charge of silver iodide particles when there is an excess of Ag+ ions during the reaction?

    <p>The particles will develop a positive charge.</p> Signup and view all the answers

    Which ions are termed potential determining ions for magnesium hydroxide?

    <p>H+ and OH-</p> Signup and view all the answers

    What characterizes the electric double layer surrounding colloidal particles?

    <p>It includes a fixed layer of charge and a diffused layer of counterions.</p> Signup and view all the answers

    What is the primary effect observed due to the distribution of charge in a colloidal particle's electric double layer?

    <p>Generation of electrokinetic or zeta potential.</p> Signup and view all the answers

    How does an increase in hydroxide concentration affect aluminum hydroxide particles?

    <p>Results in a negative charge on the particles.</p> Signup and view all the answers

    What defines the Stern double layer in colloidal systems?

    <p>The combination of a compact layer of fixed charges and a diffuse layer.</p> Signup and view all the answers

    In a colloidal reaction involving excess NaI, what is the resulting charge on the silver iodide particles?

    <p>Negative charge due to excess I- ions.</p> Signup and view all the answers

    Which term best describes the charged atmosphere formed around colloidal particles due to selective adsorption?

    <p>Electric double layer.</p> Signup and view all the answers

    What happens to the adsorbed electrolyte on sol particles when boiling occurs?

    <p>It facilitates their settling down.</p> Signup and view all the answers

    Which of the following best describes the process of complex coacervation?

    <p>The mixing of oppositely charged lyophilic colloids resulting in particle aggregation.</p> Signup and view all the answers

    How does the addition of a hydrophilic colloid affect a hydrophobic colloid?

    <p>It tends to sensitize and coagulate the hydrophobic colloid.</p> Signup and view all the answers

    What role do polymer flocculants play in a colloidal system?

    <p>They connect individual colloidal particles through electrostatic interactions.</p> Signup and view all the answers

    What is one of the main advantages of microencapsulation for drugs?

    <p>It provides protection against chemical degradation.</p> Signup and view all the answers

    Which of the following statements correctly describes sensitization?

    <p>Sensitization involves adding a colloid of opposite charge to promote coagulation.</p> Signup and view all the answers

    What is the primary factor that determines the coagulation power of an effective ion?

    <p>The valency of the ion.</p> Signup and view all the answers

    What phenomenon is responsible for the blue appearance of the sky?

    <p>Scattering of light by colloidal dust particles</p> Signup and view all the answers

    What does coacervation lead to when two lyophilic colloids are mixed?

    <p>The formation of a colloid-rich layer separate from the dispersion.</p> Signup and view all the answers

    Which of the following is NOT a common application of colloids?

    <p>Construction of bridges</p> Signup and view all the answers

    How do soap solutions function to remove dirt?

    <p>By emulsifying greasy matter and adsorbing dirt particles</p> Signup and view all the answers

    Which colloidal dispersion is used as a plasma substitute?

    <p>Colloidal hydroxyethyl starch (HES)</p> Signup and view all the answers

    What effect do ions produced by acid have on colloidal particles in milk?

    <p>They increase the charge neutralization that causes coagulation</p> Signup and view all the answers

    What is a characteristic use of colloidal silver in medicine?

    <p>It acts as an effective germicide without gastrointestinal irritation</p> Signup and view all the answers

    Which of the following materials is colloidal in nature?

    <p>Milk</p> Signup and view all the answers

    Which statement best describes the role of colloidal macromolecules in pharmaceuticals?

    <p>They are used for coating pharmaceutical products</p> Signup and view all the answers

    Study Notes

    Dispersions

    • Dispersed systems consist of two phases: particulate matter (dispersed phase) and continuous phase (dispersion medium/solvent).
    • Based on the size of the dispersed phase, three types of dispersed systems are generally considered: molecular dispersions, colloidal dispersions, and coarse dispersions.

    Introduction to Colloidal Dispersions

    • The word colloid comes from the Greek words 'kolla' (glue) and 'eidos' (like), thus colloidal particles are glue-like substances.
    • Colloidal systems consist of two phases: a dispersed phase (discontinuous phase) and a dispersion medium (continuous phase).
    • A colloid is defined as a heterogeneous (two-phase) system consisting of minute particles (1 nm to 1000 nm) microscopically dispersed into a continuous phase.
    • Examples of natural colloids include fogs, mists, smoke, and ferric hydrosol.

    Examples of Colloidal Systems

    • Foams
    • Milk
    • Fog/smoke
    • Detergents
    • Aerogel
    • Blood
    • Paints
    • Cosmetics

    Classification of Dispersed Systems

    • Molecular dispersion: Particle size less than 1 nm. Invisible in electron microscopes; pass through ultrafilters and semipermeable membranes; undergo rapid diffusion. Examples include oxygen molecules and ordinary ions.
    • Colloidal dispersion: Particle size from 1 nm to 0.5 µm. Invisible in ordinary microscopes but visible in electron microscopes; pass through filter paper but do not pass semipermeable membranes; diffuse very slowly. Examples include colloidal silver sols and natural/synthetic polymers.
    • Coarse dispersion: Particle size greater than 0.5 µm. Visible under a microscope; do not pass through normal filter paper; do not dialyze through semipermeable membranes; do not diffuse. Examples include grains of sand, emulsions, and red blood cells.

    Properties of Solutions, Colloids, and Suspensions

    Property Solution Colloid Suspension
    Particle Size 0.1-1.0 nm 1-1000 nm >1000 nm
    Settles on Standing? No No Yes
    Filter with Paper? No No Yes
    Separate by Dialysis? Yes Borderline No
    Homogeneous? Yes Borderline No

    Size and Shape of Colloidal Particles

    • Colloidal particles may have various shapes and sizes.
    • Particle shape and the dispersion medium affect surface area, attractive forces, flow, sedimentation, and osmotic pressure.
    • Size affects color. Larger sizes tend to change the color of a suspension (e.g., red gold sol to blue).

    Forces in Colloidal Particle Interactions

    • Excluded volume repulsion: The space a molecule occupies in a liquid, which is inaccessible to other molecules.
    • Van der Waals forces: Attractions or repulsions between molecules (excluding covalent, hydrogen, and electrostatic interactions).
    • Electrostatic interaction: Charged colloidal particles exert forces of attraction or repulsion. Factors such as charge of the dispersed phase, dispersion medium and mobility affect colloids.
    • Steric forces(Born repulsion): Repulsion due to overlapping electron clouds when molecules are in close proximity. This repulsion affects particle shape, conformation, and reactivity.

    Classification of Colloids

    • Physical state of dispersed phase and dispersion medium.
    • Molecular size of dispersed phase.
    • Nature of interaction between dispersed phase and dispersion medium.
    • Appearance of colloids.
    • Electric charge on dispersion phase.

    Physical State of Dispersed Phase and Dispersion Medium

    • Solid in solid (solid-sol) - e.g., coloured glass, gemstones
    • Solid in liquid (sol) - e.g., ink, blood
    • Solid in gas (aerosol) - e.g., smoke
    • Liquid in liquid (emulsion) - e.g., milk, cream
    • Liquid in gas (liquid aerosol) - e.g., fog
    • Gas in solid (solid form) - e.g., pumice stone
    • Gas in liquid (foam) - e.g, shaving cream
    • Gas in gas - (none) e.g. all gases are miscible.

    Molecular Size of the Dispersed Phase

    • Multimolecular colloids: Individual particles (atoms or small molecules) aggregate due to weak van der Waals forces (e.g., gold sol, sulphur sol).
    • Macromolecular colloids: Particles (e.g., cellulose, starch, proteins) are sufficiently large to exhibit colloidal properties.

    Appearance of Colloids (Various types)

    • Sols: Colloidal solution appearing as a fluid (e.g., dispersion of solids in liquids.)

    • Gels: Colloidal system which transforms into solid or semisolids under certain concentration/temperature (“sets”). The rigidity of a gel is due to the intertwining network trapping the dispersion medium. (e.g., jelly, butter, cheese, curd).

    Nature of interaction between dispersed phase and dispersion medium

    • Lyophilic colloids (solvent-loving): Have a strong affinity for the dispersion medium; are quite stable when separated; easy to reconstitute. Example include hydrophilic colloids (solvent is water) such as acacia, insulin in water. Types of lyophilic colloids include hydrophilic and lipophilic.

    • Lyophobic colloids (solvent-hating): Have very weak affinity for the dispersion medium; easily coagulate/are not reversible; unstable when separated. Examples include synthetic polymers, metal hydroxides, metal sols (e.g. gold sol).

    • Association colloids (amphiphilic): Have both hydrophilic and hydrophobic parts in the same molecule (e.g., surfactants soap, detergents). Exhibit different properties at different concentrations. Examples include anionic, cationic, non-ionic, and ampholytic colloids.

    Lyophilic Colloids

    • More stable than lyophobic colloids because of strong attraction between dispersed phase and dispersion medium (e.g. water).
    • Stable as solute particle is surrounded by two factors:
      • Charge
      • Solvent Layer
    • Easily reversible in nature (if dispersion medium is separated from the dispersed phase the sol can be reconstituted by simply remixing with the dispersion medium).

    Lyophobic Colloids

    • Instability, and coagulation if dispersed phase is separated from dispersion media.
    • Poorly hydrated.
    • Examples: metal hydroxides, metal sols (e.g., gold sols)

    Preparation of Lyophobic Colloids

    • Dispersion Methods: Breaking larger particles into colloidal dimensions (e.g. ball mill, colloid mill, ultrasonic treatment, Bredig's arc method).
    • Condensation Methods: Aggregating smaller particles to form particles of colloidal size (e.g. chemical reactions, change in solvent).

    Mechanical Dispersion Methods

    • Ball mill: Uses rotating vessel with metal balls to crush/disperse material in a suitable medium.
    • Colloid mill: Uses two rotating plates (fixed or opposite direction) to disperse material in a medium.

    Peptization and Ultrasonic Waves

    • The conversion from a freshly prepared precipitate to colloidal form by the addition of appropriate electrolytes is called peptization.
    • Electrolytes work by being adsorbing ions that the particles will disperse.

    Bredig's Arc Method

    • Dipping metal electrodes into the dispersion medium and striking an electric arc between these electrodes generates intense heat for metal vaporization.
    • Condensation of metal results in colloidal sized particles.

    Condensation Methods (Association Methods)

    • Chemical reactions and change in solvent are used to aggregate sub-colloidal particles.

    Oxidation, Reduction, Hydrolysis, and Double Decomposition Reactions

    • Oxidation: Addition of oxygen and removal of hydrogen (e.g., preparing colloidal sulfur by oxidizing H₂S).
    • Reduction: Addition of hydrogen or removal of oxygen (e.g., preparing gold sol with stannous chloride).
    • Hydrolysis: Breakdown of water (e.g., preparing metal hydroxides by boiling their corresponding chlorides).
    • Double Decomposition: Reactions where two compounds react to produce two new compounds. (e.g. , preparing arsenous sulfide by passing hydrogen sulfide gas ).

    Change of Solvent

    • Methods for preparing colloids by altering the solvent.
      • Thermal Condensation: Passing of hot vapours through cold water to form precipitates (e.g., mercury and sulphur).
      • Excessive Cooling: Freezing a solution of two substances to form colloids of the other substance within the first. Example, freezing a solution of water in CHCl3 or ether.
      • Exchange of Solvent : Mixing a solvent soluble in a sol that is insoluble in another substance. Adding a solution of sulfur in alcohol into an excess of water, e.g, results in a milky sulfur colloid.
      • Reducing Solubility: Adding a concentrated solution to a different liquid produces a precipitate due to supersaturation.

    Colloid Stability Mechanisms

    • Steric Stabilization: Surrounding colloidal particles with a protective layer preventing them from aggregating.
    • Electrostatic Stabilization: Providing colloidal particles with a charge to create repulsive forces between them .

    Properties of Colloids

    • Physical Properties: Heterogeneity, visibility of dispersed particles, stability, and filterability. Particle size, and color (scattering of light).
    • Optical Properties: Tyndall effect (scattering of light by colloidal particles).
    • Mechanical Properties: Brownian motion, diffusion, sedimentation, osmotic pressure, and viscosity.
    • Electrical Properties: electrical charge acquired on the surface of colloidal particles (e.g. from ion dissolution, ionization, and ion adsorption).

    Instruments of Detection

    • Ultramicroscope: Uses Tyndall effect to observe light scattered by colloidal particles.
    • Electron Microscope: Uses beams of electrons to visualize colloidal particles with high magnification.

    Importance of Light Scattering Measurements

    • Estimating particle size
    • Estimating particle shape
    • Estimating particle interactions

    Methods for purifying colloidal solutions

    • Dialysis: Separating colloidal particles from smaller solutes by using a semi-permeable membrane.
    • Electro dialysis: Increasing dialysis by applying an electrical potential.
    • Ultrafiltration: Filtering colloidal solutions by using ultrafilters (with smaller pores) under pressure.
    • Ultracentrifugation: High-speed centrifugation to separate colloidal particles from impurities (based on sedimentation).

    Mechanical Properties

    • Kinetic properties relating to particle motion.
    • Brownian Motion: rapid zig-zag motion of colloidal particles due to collisions with the dispersion medium molecules.
    • Diffusion: Movement of colloidal particles/solutes from high to low concentration regions.
    • Sedimentation: Settling of particles under the influence of gravity.
    • Osmotic Pressure: Pressure exerted by solutes in a solution.
    • Viscosity: Resistance to flow.

    Electrical Charge of Dispersion Phase

    • Colloidal particles exhibit surface charge (due to ionization of surface groups or other factors).
    • Positive Colloids: Particles carry positive charge (e.g., metal hydroxides).
    • Negative Colloids: Particles carry negative charge (e.g., Ag sol, Cu sol).

    Electrical Properties of Interfaces (various aspects)

    • Ion dissolution.
    • Ionization.
    • Ion adsorption.

    Suit Ionization

    • pH at which the colloidal particles has no electrical charge. The particles/protein is least soluble at this point.

    Osmotic Pressure

    • Method for determining the molecular weight of colloids in dilute solution.
    • Based on van't Hoff's law (π = RTC/M). Measures the pressure (π) needed to prevent osmotic flow of water.

    Viscosity

    • Resistance of a fluid to flow under applied pressure.
    • Viscosity of colloids dependent on particle shape and solvation.
    • Related to MW, shape and particle size of dispersed phase.
    • Equations for viscosity calculated using a viscometer.

    Coacervation and Microencapsulation

    • Separation of colloids and formation of a dispersion layer.
    • Formation of particles (coacervates) rich in colloids.
    • The process used to coat or encapsulate materials.
    • Coating protects material from degradation.

    Sensitization and Protective Colloidal Action

    • Addition of a hydrophilic colloid to a hydrophobic colloid to increase stability and reduce protein precipitation.
    • The hydrophobic colloid particles form a protective layer to prevent precipitation/aggregation.
    • The solution used to protect is called the protective colloid.

    Advantages and Disadvantages of Colloidal Preparations

    • Advantages: higher catalytic activity, attractive color, better taste/texture, improved solubility/absorption.
    • Disadvantages: increased toxicity, difficult preparation/stabilization, stability issues.

    Additional Advantages of Colloids

    • Dispersion of normally insoluble materials.
    • Drug delivery/antibiotics.
    • Used in paints, inks, and other products.
    • Removal of dirt particles, etc.

    Applications of Colloids

    • Paints, adhesives, and inks.
    • Water/sewage treatment, and oil recovery.
    • Research (e.g., high-resolution chromatography).
    • Medical (e.g., drug delivery, diagnostics).
    • Chemical (e.g., catalysts, rheological studies).

    Colloid-Based Delivery Systems for Therapeutics

    • Various systems for delivering drugs/treatments, based on different size ranges.
      • Microspheres
      • Microparticles
      • Emulsions
      • Liposomes
      • Micelles
      • Nanoparticles
      • Nanocrystals
      • Quantum dots

    Pharmaceutical Applications of Colloids

    • effective germicides
    • Drug delivery
    • Disease diagnosis (e.g., syphilis)
    • Plasma substitutes of proteins (e.g. starch).
    • Coating pharmaceutical products.
    • Improving solubility and stability.

    Coagulation

    • The process or term for particles aggregating and settling due to the removal of repulsive forces.
    • Causes by adding electrolytes or mixing oppositely charged sols.
    • Colloids can be precipitated.

    Hardy-Schulze Rule

    • Precipitation of a sol due to addition of electrolytes is dependent upon the valence of the precipitating ion. Higher valance ions will have a more significant precipitating power.

    Additional Colloidal Properties

    • DLVO Theory: Describe interaction, stability, and attraction/repulsion in lyophobic colloids.
    • Potential Energy Curves: Showing van der Waals attraction and electrostatic repulsion between particles, influencing stability.

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    Colloids Lecture Notes - PDF

    Description

    This quiz explores the concepts of dispersed systems, including molecular, colloidal, and coarse dispersions. Learn about the properties and examples of colloidal systems, as well as their phases and classifications. Test your knowledge on natural colloids and their applications in everyday life.

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