Colloids Overview and Comparisons
42 Questions
1 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is a colloid and how does its particle size compare to solutions and suspensions?

A colloid is a substance microscopically dispersed throughout another substance, with particle sizes between $1 nm$ and $100 nm$.

Name the two distinct phases in colloidal dispersions.

The two distinct phases are the dispersed phase and the dispersion medium.

How can colloids be made to settle, and what is this process called?

Colloids can be made to settle by the process of centrifugation.

Compare the visibility of particles in true solutions, suspensions, and colloidal solutions.

<p>True solutions have invisible particles, suspensions have visible particles, while colloidal solutions scatter light and can be observed under an ultramicroscope.</p> Signup and view all the answers

What happens to colloids when left to stand, unlike suspensions?

<p>Colloids do not settle upon standing, whereas suspensions do settle.</p> Signup and view all the answers

Describe how diffusion rates differ among true solutions, colloids, and suspensions.

<p>True solutions diffuse quickly, colloids diffuse slowly, and suspensions are unable to diffuse.</p> Signup and view all the answers

Which type of dispersion can pass through filter paper but not through animal membranes?

<p>Colloids can pass through filter paper but cannot pass through animal membranes.</p> Signup and view all the answers

What is the range of particle sizes found in colloids, and how does it compare to true solutions and suspensions?

<p>Colloidal particles range in size from 1 nm to 100 nm, which is larger than those in true solutions and smaller than those in suspensions.</p> Signup and view all the answers

How do the appearances of true solutions, suspensions, and colloids differ?

<p>True solutions appear clear and transparent, suspensions are opaque, and colloids are translucent.</p> Signup and view all the answers

What is the Tyndall effect, and why is it significant in the study of colloids?

<p>The Tyndall effect is the scattering of light by colloidal particles, making the path of a beam of light visible, which helps in identifying colloids.</p> Signup and view all the answers

Describe how the shape of colloidal particles affects their behavior within a colloidal system.

<p>The shape of colloidal particles influences their specific surface area and the attractive forces between them, affecting flow, sedimentation, and osmotic pressure.</p> Signup and view all the answers

List two examples of colloids and identify the dispersed phase and dispersion medium in each.

<p>Milk is an emulsion where fat is the dispersed phase and water is the dispersion medium. Fog is a colloid where water droplets are the dispersed phase and air is the dispersion medium.</p> Signup and view all the answers

What characteristics differentiate colloids from other types of mixtures like suspensions and solutions?

<p>Colloids cannot be filtered, can be separated by semipermeable membranes, and exhibit the Tyndall effect, unlike solutions and suspensions.</p> Signup and view all the answers

What is the Zeta potential and why is it considered more important than Nernst potential?

<p>Zeta potential is the difference in electric potential between the shear plane and the electroneutral region of a solution. It is more important than Nernst potential because the electrical double layer moves when the particle is under motion.</p> Signup and view all the answers

How does pH affect Zeta potential, and what is the significance of the isoelectric point?

<p>The Zeta potential is positive at low pH and negative at high pH, with the isoelectric point being where the Zeta potential crosses zero. This point indicates the least stability of the colloidal system.</p> Signup and view all the answers

What factors influence the thickness of the electrical double layer in relation to Zeta potential?

<p>The thickness of the double layer is influenced by the concentration of ions in solution and their valency. Higher ionic strength results in a more compressed double layer.</p> Signup and view all the answers

How does the concentration of formulation components impact Zeta potential?

<p>The concentration of formulation components can influence Zeta potential, aiding in the formulation of products that maximize stability. A suitable concentration helps maintain the desired Zeta potential.</p> Signup and view all the answers

What is the typical range of values for Zeta potential, and what does a high Zeta potential indicate about colloidal stability?

<p>Zeta potential values typically range from +100 mV to -100 mV. A high Zeta potential indicates strong repulsive forces between particles, leading to greater colloidal stability.</p> Signup and view all the answers

What happens to water when the applied pressure is too low in relation to solute concentration?

<p>Water flows into the region of higher solute concentration, moving down the concentration gradient.</p> Signup and view all the answers

How does high applied pressure affect water movement in reverse osmosis?

<p>High pressure causes water to flow into the region of lower solute concentration, against the natural concentration gradient.</p> Signup and view all the answers

What is the relationship between osmotic pressure and solute concentration differences across a membrane?

<p>Osmotic pressure is proportional to the solute concentration differences across the membrane.</p> Signup and view all the answers

Explain the role of Brownian movement in sedimentation of colloidal particles.

<p>Brownian movement keeps colloidal particles in continuous random motion, offsetting the effect of gravity that causes sedimentation.</p> Signup and view all the answers

What technique can be used to enhance sedimentation of colloidal particles, and how does it work?

<p>Ultracentrifugation can be used to apply a stronger force to promote sedimentation in a measurable manner.</p> Signup and view all the answers

Define viscosity and its significance in the context of colloidal systems.

<p>Viscosity is the resistance to flow under applied pressure and indicates the molecular weight and shape of particles in colloids.</p> Signup and view all the answers

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

<p>Spherocolloids have relatively low viscosity, while linear particles lead to higher viscosity.</p> Signup and view all the answers

What occurs to the flow rate of a liquid as its viscosity increases?

<p>As viscosity increases, a greater applied force is required to make the liquid flow at a particular rate.</p> Signup and view all the answers

What happens to the viscosity of a colloidal system when linear colloidal particles coil into a sphere?

<p>The viscosity of the system decreases as the shape changes from linear to spherical.</p> Signup and view all the answers

How does the electric charge on colloidal particles affect their behavior in a solution?

<p>The electric charge causes the particles to repel each other, preventing them from clustering and settling.</p> Signup and view all the answers

What is the Electric Double Layer (EDL) in colloidal systems?

<p>The Electric Double Layer is the layer surrounding a colloidal particle, consisting of the charged surface, Stern layer, and diffuse layer.</p> Signup and view all the answers

What contributes to the formation of zeta potential in colloidal dispersions?

<p>Zeta potential arises from the electrokinetic potential of the charged colloidal particles in a dispersion.</p> Signup and view all the answers

Describe the components of the Electric Double Layer around a colloidal particle.

<p>The Electric Double Layer consists of a surface charge, a Stern layer of counter-ions, and a diffuse layer of solvent ions.</p> Signup and view all the answers

What role does thermal motion play in the distribution of charges around colloidal particles?

<p>Thermal motion influences the arrangement and distribution of positive and negative ions surrounding the colloidal particles.</p> Signup and view all the answers

How does the dissociation of molecular electrolytes contribute to the charge on colloidal particles?

<p>The dissociation of molecular electrolytes leads to the formation of charged ions on the particle surfaces, contributing to their overall charge.</p> Signup and view all the answers

What is the significance of counter-ions in the Stern layer of the Electric Double Layer?

<p>Counter-ions in the Stern layer are attracted to the particle surface, stabilizing the colloid through electrostatic interactions.</p> Signup and view all the answers

What type of colloid is formed when a solid is dispersed in a gas? Provide an example.

<p>Aerosol; examples include smoke and dust.</p> Signup and view all the answers

Define lyophilic colloids and give two examples.

<p>Lyophilic colloids are solvent-loving colloids with strong interaction with the dispersion medium; examples are acacia in water and gelatin.</p> Signup and view all the answers

What happens to lyophobic colloids upon precipitation, and what aids their stabilization?

<p>Lyophobic colloids cannot return to a colloidal state once precipitated and require stabilizing agents to be preserved.</p> Signup and view all the answers

Name the type of colloid formed when a liquid is dispersed in a solid and provide an example.

<p>Gel; examples include cheese butter and jellies.</p> Signup and view all the answers

Identify two types of lyophobic colloids and provide an example of each.

<p>Hydrophobic colloids, like polystyrene; and lipophobic colloids, such as water-in-oil emulsions.</p> Signup and view all the answers

What is an emulsion, and can you give two examples?

<p>An emulsion is a colloid where liquid droplets are dispersed in another liquid; examples include milk and hair cream.</p> Signup and view all the answers

List two examples of solid sols and explain what they consist of.

<p>Gem stones and pumice stone; they consist of solid particles dispersed in a solid medium.</p> Signup and view all the answers

What distinguishes hydrophobic colloids from hydrophilic colloids?

<p>Hydrophobic colloids have little to no hydration in water, while hydrophilic colloids interact strongly with water.</p> Signup and view all the answers

Flashcards

Dispersed Phase

The phase that's dispersed throughout the other phase. It's also known as the internal or discontinuous phase.

Dispersion Medium

The phase that surrounds the dispersed phase. It's also known as the external or continuous phase.

Colloid Particle Size

Colloids have particle sizes between 1 nm and 100 nm, larger than true solutions but smaller than suspensions.

Tyndall Effect

The Tyndall effect is the scattering of light by colloids, making the beam visible. This is because colloid particles are large enough to scatter light.

Signup and view all the flashcards

Specific Surface Area

The specific surface area of a colloid is its surface area per unit weight or volume. The more extended the shape of the colloidal particle, the higher its specific surface area.

Signup and view all the flashcards

What is a colloid?

A colloid is a mixture where one substance is dispersed evenly throughout another substance, but the particles are much larger than in a true solution.

Signup and view all the flashcards

Types of Colloids

Colloids are classified based on the state of the dispersed phase and the dispersion medium. Some common types include sols, gels, emulsions, and foams.

Signup and view all the flashcards

Homogeneous vs. Heterogeneous

Colloids appear homogeneous to the naked eye, but they're actually heterogeneous mixtures. This means the dispersed particles are evenly distributed but not dissolved.

Signup and view all the flashcards

Particle Size in Colloids

Colloidal particles are larger than molecules in a true solution, but smaller than particles in a suspension. This size range is key to their unique properties.

Signup and view all the flashcards

Sedimentation in Colloids

Colloidal particles are too small to settle out by gravity alone. They remain suspended in the dispersion medium.

Signup and view all the flashcards

Diffusion in Colloids

Colloids diffuse much more slowly than true solutions, but they do diffuse over time.

Signup and view all the flashcards

Filterability of Colloids

Colloids can pass through filter paper, but they cannot pass through membranes like animal cell membranes.

Signup and view all the flashcards

Solid sol

A type of colloid where the dispersed phase (internal phase) is solid and the dispersion medium (external phase) is solid. Examples are gemstones and some alloys.

Signup and view all the flashcards

Sol

A type of colloid where the dispersed phase is solid and the dispersion medium is liquid. Examples include paints and cell fluids.

Signup and view all the flashcards

Gel

A type of colloid where the dispersed phase is liquid and the dispersion medium is solid. Examples include cheese, butter, and jellies.

Signup and view all the flashcards

Emulsion

A type of colloid where the dispersed phase is liquid and the dispersion medium is liquid. Examples include milk and hair cream.

Signup and view all the flashcards

Lyophilic colloid

A type of colloid where the dispersed phase shows a strong affinity for the dispersion medium.

Signup and view all the flashcards

Lyophobic colloid

A type of colloid where the dispersed phase shows little affinity (or even aversion) for the dispersion medium.

Signup and view all the flashcards

Hydrophobic colloid

A type of lyophobic colloid where the dispersion medium is water and the particles are not hydrated. Examples include polystyrene steroids, gold, silver, and sulfur.

Signup and view all the flashcards

Lipophobic colloid

A type of lyophobic colloid where the dispersion medium is oil and the particles are not hydrated.

Signup and view all the flashcards

Zeta potential

The difference in electrical potential between the shear plane and the electroneutral region of the solution.

Signup and view all the flashcards

Isoelectric Point (IEP)

The point where the zeta potential becomes zero, indicating a neutral charge on the particle.

Signup and view all the flashcards

Double Layer Thickness

The thickness of the electrical double layer depends on the concentration of ions in solution and their valency.

Signup and view all the flashcards

Ionic Strength and Zeta Potential

The higher the ionic strength, the more compressed the electrical double layer becomes.

Signup and view all the flashcards

pH and Zeta Potential

The pH of the solution significantly affects Zeta potential, with higher pH leading to a generally more negative potential.

Signup and view all the flashcards

Osmotic Pressure

The pressure required to prevent the flow of water into a region of higher solute concentration across a semi-permeable membrane.

Signup and view all the flashcards

Osmosis

Describes the movement of water molecules across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Signup and view all the flashcards

Reverse Osmosis

A phenomenon where the flow of water molecules is reversed due to applying pressure greater than the osmotic pressure. It moves from a region of higher solute concentration to one with lower concentration.

Signup and view all the flashcards

Viscosity

The resistance a fluid exhibits to flow when an external force is applied. It is influenced by the size and shape of particles in the fluid.

Signup and view all the flashcards

Brownian Motion in Colloids

Colloids exhibit Brownian motion, a continuous random movement of their dispersed particles due to collisions with the solvent molecules.

Signup and view all the flashcards

Ultracentrifugation

A method used to separate colloidal particles based on their size and density by applying a strong force.

Signup and view all the flashcards

Viscosity of Colloidal Dispersions

Colloidal dispersions with spherical particles have lower viscosity compared to those with linear particles.

Signup and view all the flashcards

Charged Colloidal Particles

The particles of a colloidal solution are electrically charged and carry the same type of charge, either negative or positive. This prevents them from clumping together and settling down.

Signup and view all the flashcards

Origin of Charge on Colloids

The charge on colloidal particles arises from the dissociation of molecular electrolytes on their surface. For example, As2S3 becomes negatively charged because H2S adsorbs onto its surface and releases H+ ions, leaving behind S-2 ions.

Signup and view all the flashcards

Electric Double Layer (EDL)

This is a layer around each colloidal particle that consists of charged ions. It forms because the negatively charged particles attract positively charged ions from the surrounding medium.

Signup and view all the flashcards

Components of EDL

EDL consists of the charged surface of the particle, a layer of tightly bound counter-ions (Stern layer), and a diffuse layer with free ions with a higher concentration of counter-ions. The EDL is electrically neutral.

Signup and view all the flashcards

Zeta Potential (ζ-potential)

It refers to the potential difference between the surface of the charged particle and the bulk of the solution. It indicates the strength of the electrical double layer, which is important for colloid stability.

Signup and view all the flashcards

Electrophoresis

The movement of charged colloidal particles in an electric field. This occurs because the particles are attracted to the electrode with the opposite charge.

Signup and view all the flashcards

Electroosmosis

The movement of a liquid relative to a stationary charged surface due to an applied electric field. It happens because the electric field drags the liquid along with the counter-ions in the diffuse layer.

Signup and view all the flashcards

Viscosity Change with Coiling

The viscosity of a system containing linear colloidal particles decreases if the particles coil up into spheres. This is because the coiled particles have a lower surface area and interact less with the surrounding fluid, reducing friction.

Signup and view all the flashcards

Study Notes

Colloids

  • Colloids are substances microscopically dispersed throughout another substance.
  • The term "colloid" originates from the Greek word "kolla", meaning glue. Colloidal particles resemble glue-like substances.
  • Colloids can be made to settle by centrifugation.
  • Dispersed systems consist of particulate matter (disperse phase) distributed throughout a continuous phase (dispersion medium).
  • Colloidal systems are classified into colloidal dispersions (e.g., colloidal silver sols, natural & synthetic polymers) and coarse dispersions (>0.5 µm) (e.g., emulsions, suspensions).

Properties of Colloids

  • Particle Size: Colloidal particles have a size between 1 nm and 100 nm.
  • Sedimentation: Colloidal particles do not settle, unlike suspensions.
  • Diffusion: Colloidal particles diffuse slowly compared to true solutions.
  • Visibility: Colloidal particles are typically invisible to the naked eye but can be visible via a microscope or by scattering light.
  • Filterability: Colloids cannot be filtered through typical filter paper but can pass through semipermeable membranes.
  • Appearance: True solutions are clear and transparent. Suspensions are opaque (cloudy). Colloidal solutions appear translucent.

Types of Colloids

  • Colloids are classified based on the physical state of the dispersed phase and dispersion medium.
  • Examples:
    • Sols (solid in liquid): Gemstones, paints, cell fluids
    • Gels (liquid in solid): Cheese, butter, jellies
    • Emulsions (liquid in liquid): Milk, hair cream
    • Aerosols (solid or liquid in gas): Smoke, fog, mists, insecticide sprays
    • Solid sols (solid in solid ): Pumice stone, foam rubber, froth
    • Foam (gas in liquid): Whipped cream, soap lather

Lyophilic colloids

  • Lyophilic colloids exhibit strong interactions with the dispersion medium.
  • They are often solvated (i.e., the particles are surrounded by molecules of the medium).
  • Lyophilic colloids are typically solids in liquids; examples include hydrophilic colloids.
    • True solutions of acacia or povidone in water
    • Gelled solutions of gelatin and starch
    • Particulate dispersion of bentonite in water

Lyophobic colloids

  • Lyophobic colloids have little interaction (or affinity) with the dispersion medium.
  • These particles are not solvated.
  • Lyophobic colloids need stabilizing agents.
  • Lyophobic colloids are unstable and are usually irreversible.
  • Examples include colloidal solutions of gold, silver, iron(III) hydroxide (Fe(OH)₃), and arsenic sulfide (Asâ‚‚S₃).

Association Colloids

  • Association colloids are molecules that have both hydrophilic and lipophilic parts.
  • They form micelles at higher concentrations.
  • Examples include anionic, cationic, and non-ionic surfactants.

Optical Properties (Colloids)

  • Faraday Tyndall Effect: Light scattering by the colloidal particles makes the path of light visible. This is stronger in lyophobic colloids.
  • Electron microscopy: The shorter wavelength of electrons allows for much higher resolution in identifying the shapes, size and structures of particles in colloids which conventional optical microscopes cannot reveal.
  • Light Scattering: Used to measure the molecular weight, shape and particle size of colloids.

Kinetic Properties of Colloids

  • Brownian Motion: Continuous, random motion of colloidal particles due to collisions with the solvent molecules.
  • Diffusion: The movement of molecules or particles from an area of high concentration to an area of low concentration.
  • Osmotic Pressure: The pressure needed to prevent the flow of solvent across a semipermeable membrane.
  • Sedimentation: The process where heavier particles settle out of a solution at equilibrium, affected by gravity.
  • Viscosity: The resistance of a fluid to flow.

Electrical Properties of Colloids

  • Electric Double Layer: The layer surrounding a charged particle in a colloid that has a film of counter-charged dispersion medium with counterions.
  • Zeta Potential: The potential at the boundary of the electrical double layer, usually denoted using the Greek letter zeta (ζ).
  • Factors affecting zeta potential: pH, thickness of the double layer, concentration of a formulation component.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Colloids BTF3823 PDF

Description

Explore the fascinating world of colloids through this quiz. You'll discover their unique properties, how they differ from true solutions and suspensions, and the significance of the Tyndall effect. Test your knowledge on particle sizes, phases, and examples in colloidal dispersions.

More Like This

Mastering Suspensions and Colloids
6 questions

Mastering Suspensions and Colloids

HappierConsciousness5401 avatar
HappierConsciousness5401
Colloidal Suspensions Quiz
3 questions

Colloidal Suspensions Quiz

WellManagedFreedom avatar
WellManagedFreedom
Colloids and Suspensions Quiz
6 questions

Tyndall Effect: Colloids and Suspensions Quiz and Flashcards

CredibleHill avatar
CredibleHill
Colloidal Chemistry Basics
34 questions

Colloidal Chemistry Basics

EnrapturedScandium avatar
EnrapturedScandium
Use Quizgecko on...
Browser
Open
Browser
Browser