Colloidal Chemistry Quiz

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Questions and Answers

Which statement about lyophobic dispersions is accurate?

They are usually dispersions of metals or inorganic crystals. (correct)

They have low interfacial free energy.

They are generally thermodynamically stable.

They form spontaneously in solution.

What is a key characteristic of lyophilic materials?

They typically do not disperse when added to a solvent.

They are stabilized by electrical repulsion.

They spontaneously disperse in a solvent due to increased entropy. (correct)

They generally require additional energy to remain dispersed.

How is the stability of lyophobic sols maintained?

By the presence of stagnant solvent layers.

Through the presence of electric charges on particle surfaces. (correct)

By low interfacial surface-free energy.

Through solvation of surrounding particles.

What is the state of free energy in the formation of lyophobic dispersions?

It is positive, indicating the formation is unlikely. Signup and view all the answers

What primarily controls the stability of lyophilic sols?

Solvation of particles and their electrical charge. Signup and view all the answers

What is the particle size range of colloidal dispersions?

1nm – 500nm Signup and view all the answers

Which of the following represents a colloidal dispersion in a solid state?

Gelatin Signup and view all the answers

What is the characteristic of a true solution regarding particle size?

Less than 1nm Signup and view all the answers

Which of the following is a characteristic of coarse dispersions?

They contain particles between 10 – 50μm. Signup and view all the answers

In terms of dispersions, which of the following is true about the interaction between the dispersed phase and the continuous medium?

It is a characteristic of all dispersion systems. Signup and view all the answers

What type of colloidal dispersion is represented by smoke?

Solid aerosol Signup and view all the answers

Which of the following is NOT a characteristic of colloidal systems?

Their particles are visible under a microscope. Signup and view all the answers

What is the defining range of particle size for suspensions?

Greater than 1000nm Signup and view all the answers

How does the viscosity of a lyophobic colloidal dispersion compare to that of a lyophilic system?

The viscosity of the lyophobic remains low even at high concentrations. Signup and view all the answers

What effect does the concentration of amphiphiles have on the viscosity of a system?

Viscosity increases due to the increase in micelle numbers. Signup and view all the answers

Why do lyophobic colloidal particles not readily solvate?

They exhibit high repulsion between each other. Signup and view all the answers

What relationship exists between viscosity and particle concentration in a lyophilic system?

Viscosity increases with the concentration until a gel forms. Signup and view all the answers

What occurs at sufficiently high concentrations of a dispersed phase in a colloidal system?

A gel may form, indicating changes in viscosity and solvation effects. Signup and view all the answers

What is the main characteristic of lyophobic colloids?

Little interaction with the dispersion medium Signup and view all the answers

Which of the following correctly defines Stoke's diameter?

It describes an equivalent sphere for sedimentation rate comparison. Signup and view all the answers

Which type of colloid consists of particles that swell spontaneously in water?

Both B and C Signup and view all the answers

What type of particles typically compose lyophobic colloids?

Inorganic particles like gold and silver Signup and view all the answers

What is a common stabilization requirement for hydrophobic colloids?

They need surfactants or stabilizing agents. Signup and view all the answers

Which of the following describes the nature of lyophilic colloids?

They consist of aggregates of molecules that swell in water. Signup and view all the answers

Which statement is TRUE regarding the dispersed phase in lyophobic colloids?

They lack solvation by the continuous phase. Signup and view all the answers

What do amphiphilic molecules in a colloid typically form?

Micelles composed of hydrophobic tails Signup and view all the answers

What role do surfactants play in the stabilization of particles in a colloidal system?

Lower the interfacial energy of the system. Signup and view all the answers

What phenomenon occurs when sufficient salt is added to a lyophobic colloid?

Agglomeration and sedimentation of particles. Signup and view all the answers

How do electrolytes affect lyophobic colloids compared to lyophilic colloids?

Lyophilic colloids are more sensitive to added electrolytes. Signup and view all the answers

What type of interaction helps stabilize colloidal particles by creating a protective solvent sheath?

Repulsion from like charges. Signup and view all the answers

At what condition are proteins more sensitive to the addition of electrolytes?

At their isoelectric points. Signup and view all the answers

What is the effect of hydration on the ions of an electrolyte in colloidal systems?

It decreases the tendency of ions to aggregate. Signup and view all the answers

What is formed when lyophilic colloids are salted out?

Amorphous droplets known as coacervates. Signup and view all the answers

How do polyelectrolytes or polymer molecules affect lyophobic colloids?

They bridge two particles and stabilize them. Signup and view all the answers

What is the primary characteristic of lyophobic sols?

They can be flocculated and exist as a two-phase system. Signup and view all the answers

What type of charge do the flat 'faces' of clay particles typically carry?

Negative charge Signup and view all the answers

Which of the following is an example of a lyophobic sol?

Milk of Magnesia Signup and view all the answers

What phenomenon do gels made from hydrophilic particles exhibit due to their structure?

Thixotropy Signup and view all the answers

What structural arrangement is formed when the particles of clay flocculate?

Card house floc Signup and view all the answers

What is a characteristic feature of hydrophobic colloidal particles in dispersion?

Are predominantly spherical or ellipsoidal. Signup and view all the answers

How does the shape of colloidal particles affect their interaction with the dispersion medium?

Extended particles increase specific surface for interactions. Signup and view all the answers

Which type of interactions stabilize lyophobic sols?

Ionic and van der Waals forces Signup and view all the answers

Study Notes

Colloidal Dispersions: Introduction and Properties

Colloidal dispersions are heterogeneous systems composed of a dispersed phase (very fine particles) and a dispersion medium (continuous phase).
Particle sizes in disperse systems (true solution, colloidal dispersions, fine dispersions, coarse dispersions) are categorized according to specific ranges, with colloids falling between true solutions and fine dispersions: <1nm (true solution), 1nm - 500nm = 0.5µm (colloidal dispersions), 500nm = 0.5µm - 10µm (fine dispersions), 10 - 50µm (coarse dispersions).
Colloidal systems are classified based on: the physical state of the dispersed phase and dispersion medium; particle size; and the interaction between the dispersed phase and the dispersion medium.
Common examples of colloidal dispersions include:
- Gas dispersed in gas: Fog, mist, smoke (aerosols)
- Liquid dispersed in gas: Fog, mist, aerosols (aerosols)
- Solid dispersed in gas: Smoke, dust
- Liquid dispersed in liquid: Emulsions (milk, mayonnaise)
- Solid dispersed in liquid: Sols (blood, antacids), suspensions
- Gas dispersed in liquid: Foam (whipped cream)
- Liquid dispersed in solid: Solid foam (styrofoam)
- Solid dispersed in solid: Gel (agar, gelatin)
- Solid dispersed in solid: solid sol & suspension

Particle Size and Size Distribution

Colloidal particles range in size from 1-1000nm, distinguishing them from larger suspensions(>1000nm) and smaller true solutions(<1nm).
Size measurements can be determined through osmotic pressure, sedimentation, and light scattering
Size is determined by diameter, but asymmetrical particles are measured by Stokes' diameter.
The size of particles is important for behavior, particularly in the context of absorption for solid aerosols, which must be between 1-5µm and not exceed 10µm.

Interaction Between Dispersed Phase and Dispersion Medium

Lyophilic colloids ("liquid loving"): have strong attractions between the dispersed phase and the dispersion medium.
Lyophobic colloids ("liquid hating"): have weak interactions between the dispersed phase and the dispersion medium, thus needing stabilizing agents.
Association/amphiphilic colloids: dispersed phase consists of aggregates (micelles) of small organic molecules or ions, and their size is below the colloidal range. A portion of them is either hydrophilic or lipophilic, depending on the medium (aqueous, non-aqueous).
Water-based colloids with inorganic dispersed phases are lyophobic (e.g., gold).
Some lyophobic colloids have lyophilic properties (e.g., silica and alumina hydrosols).

Dispersion Medium is Water

Hydrophilic colloids, in water, disperse spontaneously and have high affinity (swell).
Hydrophobic colloids, in water, are unstable and need stabilizing agents.

Lyophilic and Lyophobic Preparations

Lyophobic colloids cannot be directly prepared by mixing; special methods and stabilizers are needed.
Mechanical reduction methods (colloidal mill, hammer, ball jet) or ultrasonic vibration reduce particle size.
Condensation methods (physical and chemical, using processes like displacement, hydrolysis, and oxidation-reduction) produce the colloid.
Lyophilic colloids are generally made directly by mixing.

Colloid Properties for Molecular Weight Determination

Properties for molecular weight determination include Tyndall effect, viscosity, and osmotic pressure.

Electrical Properties of Colloids

Most surfaces acquire a surface charge when in contact with an aqueous medium, due to: (1.) ion dissolution; (2.) ionization of surface groups; (3.) ion adsorption.
Particles of a given colloid have the same charge, repelling one another. Neutralized charges can cause precipitation.
Electrophoresis is used for measuring zeta potential (charge of colloidal particles).

Terminology and Additional Properties

Imbibition: Taking up liquid by a solid or gel, without considerable volume increase.
Swelling: Taking up liquid by a gel, with volume increase.
Syneresis: A great interaction between dispersed phase particles and dispersed medium squeezed out as droplets, causing gel shrinkage.
Xerogels are gels with the liquid vehicle removed, leaving a polymer framework.
Examples of xerogels include sheet gelatin, acacia tears, and tragacanth flakes.
Lyophobic sols (e.g., Aluminum Hydroxide Gel, USP) can be flocculated, forming a 2-phase system where the sol appears as a continuous floccule.
Clay suspensions are an example of a lyophobic system composed of plate-like particles held together by weak forces (e.g., van der Waals forces).
Properties such as flow, sedimentation, and osmotic pressure are influenced by colloidal particle shapes.

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Description

Test your knowledge of colloidal chemistry with this quiz covering lyophobic and lyophilic dispersions. From particle size ranges to characteristics of true solutions, this quiz challenges your understanding of the critical concepts in colloidal systems. Perfect for students studying colloidal chemistry.