11.5 Colloids
3 min read•june 25, 2024
are fascinating mixtures that exist between solutions and . They're all around us, from milk to fog to mayonnaise. Unlike solutions or suspensions, particles stay suspended due to constant random motion, creating unique properties.
One key feature of colloids is the , where light scatters visibly through the mixture. This helps identify colloids and sets them apart from solutions and suspensions. Colloids can be prepared and stabilized in various ways, making them crucial in many applications.
Colloids
Colloids vs solutions and suspensions
Top images from around the web for Colloids vs solutions and suspensions
Colloid Chemistry Introduction View original
Is this image relevant?
Colloid Chemistry Introduction View original
Is this image relevant?
Soil Colloids – Soils Laboratory Manual View original
Is this image relevant?
Colloid Chemistry Introduction View original
Is this image relevant?
Colloid Chemistry Introduction View original
Is this image relevant?
1 of 3
Top images from around the web for Colloids vs solutions and suspensions
Colloid Chemistry Introduction View original
Is this image relevant?
Colloid Chemistry Introduction View original
Is this image relevant?
Soil Colloids – Soils Laboratory Manual View original
Is this image relevant?
Colloid Chemistry Introduction View original
Is this image relevant?
Colloid Chemistry Introduction View original
Is this image relevant?
1 of 3
- Colloids exist as an intermediate state between solutions and suspensions with particle sizes ranging from 1-1000 nm (milk, fog, mayonnaise, )
- Particles remain suspended and do not settle over time due to constant random motion ()
- Solutions are homogeneous mixtures where solute particles are smaller than 1 nm (salt water, sugar water, air)
- Particles are not visible and do not scatter light
- Suspensions are heterogeneous mixtures with particle sizes greater than 1000 nm (sand in water, dust in air)
- Particles settle over time due to the force of gravity
Tyndall effect in colloid identification
- involves the scattering of light by colloidal particles when light passes through a colloid
- Scattered light appears as a visible beam or cone
- Tyndall effect serves as a characteristic property of colloids and can be used to distinguish them from solutions and suspensions
- Solutions do not exhibit the Tyndall effect
- Suspensions may exhibit the Tyndall effect, but particles eventually settle over time
Preparation and stability of colloids
- Methods for preparing colloidal systems include:
- Dispersion methods
- Mechanical dispersion involves grinding or homogenization to break down larger particles
- Electrical dispersion utilizes electrodispersion techniques
- Condensation methods
- Physical condensation occurs through processes like vapor condensation
- Chemical condensation involves precipitation or hydrolysis reactions
- Dispersion methods
- Factors affecting colloidal stability:
- occurs when particles with like charges repel each other, preventing aggregation and maintaining stability
- involves the adsorption of polymers or surfactants on particle surfaces, creating a physical barrier that prevents particle aggregation
- measures the electrical potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle
- Higher zeta potential (positive or negative) indicates greater stability
- and are processes that destabilize colloids
- Flocculation is the reversible aggregation of particles
- Coagulation is the irreversible aggregation leading to sedimentation
Types and Applications of Colloids
- : A colloidal dispersion of solid particles in a liquid medium
- : A semi-solid colloidal system where the forms a network throughout the continuous phase
- Surfactants: Molecules that lower surface tension between two liquids or between a liquid and a solid
- Form micelles in , which are important for various applications including detergents and drug delivery
- : A separation technique used to remove small molecules from a colloidal mixture by allowing them to pass through a semi-permeable membrane
Key Terms to Review (27)
Brownian Motion: Brownian motion is the random movement of particles suspended in a fluid (liquid or gas) resulting from their collision with the fast-moving molecules in the fluid. This constant, random motion of particles is a fundamental characteristic of the particulate nature of matter and the thermal energy that is present.
Coagulation: Coagulation is the process by which a colloidal dispersion, such as a suspension or emulsion, transforms from a liquid to a semi-solid or solid state. This transition occurs when the dispersed particles in the colloid aggregate and form a three-dimensional network, resulting in the thickening or solidification of the system.
Colloid: A colloid is a heterogeneous mixture in which one substance is dispersed evenly throughout another substance, with the dispersed particles being larger than individual molecules but small enough to remain suspended and not settle out. Colloids are an important class of materials that exhibit unique properties and have numerous applications in various fields.
Colloidal dispersions: Colloidal dispersions are mixtures where fine particles are dispersed within a continuous medium without settling out. These particles range in size from 1 to 1000 nanometers.
Colloids: Colloids are mixtures where one substance is dispersed evenly throughout another but does not dissolve. The dispersed particles are typically between 1 and 1000 nanometers in size.
Condensation Method: The condensation method is a technique used in the formation of colloids, where a substance is transformed from a gaseous state into a colloidal dispersion. This process involves the nucleation and growth of particles within a supersaturated vapor, resulting in the creation of a stable colloidal system.
Cottrell: The Cottrell equation describes the change in current over time during the reduction or oxidation of a species at an electrode surface in an unstirred solution. It is key for understanding electrochemical processes involving diffusion control.
Dialysis: Dialysis is a process that involves the selective diffusion of solutes and the removal of excess water from the body. It is a critical medical procedure used to filter waste and excess water from the blood when the kidneys are unable to perform this function effectively.
Dispersed phase: The dispersed phase is the phase in a colloidal system that consists of particles distributed throughout another substance, known as the continuous phase. These particles can range in size from 1 nanometer to 1 micrometer.
Dispersion Method: The dispersion method is a technique used to create colloids, where larger particles or molecules are dispersed and suspended within a continuous medium. This process involves breaking down larger entities into smaller, evenly distributed particles that remain stable within the surrounding medium.
Electrostatic Stabilization: Electrostatic stabilization is a mechanism that helps maintain the stability and dispersion of colloidal particles in a solution. It occurs when the particles acquire a net electrical charge, creating repulsive forces that prevent the particles from aggregating and settling out of the solution.
Emulsifying agent: An emulsifying agent is a substance that stabilizes an emulsion by increasing its kinetic stability. It allows the mixing of two immiscible liquids, such as oil and water.
Emulsion: An emulsion is a type of colloid where two immiscible liquids are dispersed within each other, typically with one liquid forming droplets within the other. Emulsions often require an emulsifying agent to stabilize the mixture.
Emulsion: An emulsion is a mixture of two immiscible liquids, such as oil and water, where one liquid is dispersed as small droplets throughout the other liquid. This unique dispersion of liquids creates a stable, heterogeneous system that has various applications in chemistry, biology, and everyday life.
Flocculation: Flocculation is a process in which colloidal particles come together to form larger aggregates called flocs. This process is driven by the destabilization of the colloidal system, leading to the formation of these larger, more easily settleable particles.
Gel: A gel is a semi-solid system in which a liquid is dispersed within a solid network, forming a three-dimensional structure. Gels exhibit properties of both solids and liquids.
Gel: A gel is a semi-solid colloidal system consisting of a network of solid particles dispersed in a liquid medium. It exhibits both solid-like and liquid-like properties, with the ability to flow under stress but maintain a defined shape at rest.
Micelle: A micelle is a cluster of surfactant molecules that form a spherical or cylindrical structure in an aqueous solution. These self-assembled aggregates play a crucial role in the behavior and properties of colloidal systems.
Sol: A sol is a colloidal suspension of solid particles in a liquid medium. It is a type of colloid where the dispersed phase is solid and the continuous phase is a liquid, typically water. Sols are an important class of colloids with various applications in chemistry, biology, and material science.
Solution: A solution is a homogeneous mixture composed of two or more substances. In a solution, a solute is dissolved in a solvent, resulting in a single phase with a uniform composition and properties throughout.
Steric Stabilization: Steric stabilization is a mechanism by which colloid particles are prevented from aggregating or flocculating due to the presence of adsorbed macromolecules or solvated polymer chains that create a physical barrier around the particles, preventing close approach and subsequent coagulation.
Surfactant: A surfactant, or surface-active agent, is a compound that reduces the surface tension of a liquid, allowing easier spreading and penetration. Surfactants are widely used in various applications, including detergents, emulsifiers, and stabilizers in colloidal systems.
Suspension: A suspension is a heterogeneous mixture in which particles of a finely divided solid substance are dispersed throughout a liquid or gas medium. The particles in a suspension are large enough to be visible to the naked eye and do not dissolve in the medium.
Suspensions: Suspensions are heterogeneous mixtures where solid particles are dispersed in a liquid or gas, but are large enough that they eventually settle out. They can be separated by filtration due to the size of the particles.
Tyndall effect: Tyndall effect is the scattering of light by particles in a colloid or in very fine suspensions. This scattering makes a beam of light visible when viewed from the side.
Tyndall Effect: The Tyndall effect is the scattering of light by particles suspended in a medium, such as a colloid. It occurs when light passes through a colloid, making the path of the light beam visible.
Zeta Potential: Zeta potential is a measure of the magnitude of the electrostatic or electrical potential difference between the surface of a colloidal particle and the surrounding medium in which the particle is suspended. It is an important factor in understanding the stability and behavior of colloidal systems.