Self Assessment Questions for Colloids

Question 1

Explain what differentiates colloids from other disperse systems?

Answer 1

Particle sizes that are between molecular (solution) and coarse (suspension) dispersions –> remain evenly distributed without spreading out, also its Heterogeneous

• Suspensions: components will eventually settle out
• Solutions: Homogeneous

Colloids scatter light (tyndall effect) and colloidal particles are typically many times larger than the molecules of the dispersion medium.

Question 2

Discuss the important features of the colloidal disperse system and their implications.

Answer 2

• Large surface-to-volume ratio of the dispersed particles
• A significant proportion of the colloidal molecules lie within, or close to, the interfacial region. Hence, the interfacial region has significant control over the properties of colloids

Question 3

What is an amphiphilic colloid? How is it formed?

Answer 3

• Part hydrophilic, part hydrophobic colloid
• Formed by amphiphiles or surface active agents (surfactants) at concentration > CMC

Question 4

Compare and contrast lyophilic colloids, amphiphilic collioids and lyobphobic colloids.

Answer 4

Lyopholic colloids

• Large organic molecule in colloidal size range
• Dispersed phase has affinity for the dispersion medium
• Affinity of water allows molecules of dispersed phase to be solvated
• Viscocity increases by presence of dispersed phase (solution may form gel at high sonc)
• Formation of the colloid is spontaenous
• Stable dispersion in presence of electrolytes

Amphiphilic colloids

• Aggregates (micelles) - monomer size bellow colloidal range
• Lipophilic portions are solvated ( micelles formed spontaneously at conc above CMC)
• Viscocity increases as micelle conc increases
• CMC decreases with electrolytes

Lyophobic colloids

• Inorganic particles (eg gold, silver); water; insolulbe drugs; clays; oil
• Dispersion phase has little attraction for dispersed medium
• little solvation
• Not formed spontaneously (prepared by mechanical agitation )
• No change in visocity
• Unstable dispersion in presence of electrolyes even with low conc

Question 5

Describe four ways of differentiating between a solution and a colloid

Answer 5

• Colloid are heterogeneous, solutions are homogeneous
• Colloid particle size 1nm –> 1 um, solution particle size <1.0nm
• Colloids are translucent while solutions are transparent
• Colloids scatter light, light passes through solutions

Question 6

Describe a method of purifying a colloid (eg a protein solution) which is contaminated with large particles and electrolytes

Answer 6

Dialysis is the process which is used for the separation of crystalloids from a colloid by filtration or diffusion through parchment paper or animal membrane. The apparatus employed for this purpose is called dialyser. This process is based on the fact that membranes contain very small pores through which only dissolved molecules and ions of the true solution can pass readily.

Question 7

What are the optical properties of colloidal particles ? Give examples of their applications

Answer 7

Turbidity (light scattering), due to the size of colloidal particles, this is achievable

> Allows measurement of MW of colloids + shape and size of colloidal particles

Question 8

Describe the process of osmosis and the application of osmotic pressure in assessing colloids

Answer 8

Osmosis is the movement of water or other solvent through a plasma membrane from a region of low solute concentration to a region of high solute concentration

• provides measurable effect
• eliminates the effect of small molecule to which membrane is permeable
• For M_n< 10⁴, the method won’t work due to the permeability of these molecules
• For M_n > 10⁶, the osmotic pressure is too small to be determined accurate

Question 9

Which kinetic properties of colloids can be used to measure molecular weight of a polymer? Explain how

Answer 9

Osmotic pressure and sedimentation

• Intensity and angle of scattered light is related to the size and weight of a molecule (Rayleigh equation)
• Molecules that are larger in size or have a higher molecular weight will scatter more light than lighter or smaller molecules

Use equation for sedimentation

Question 10

How can the viscosity of pharmaceutical products be affected by the formulation?

Answer 10

temperature and pressure

Increased temp = decreased viscocity

Question 11

What kind of colloids produce viscosity?

Answer 11

Lyophilic and amphiphilic colloids