Colloids problems and solutions

  1. What is a colloid? Solution: A colloid is a type of homogeneous mixture where tiny particles of one substance are dispersed, but not dissolved, in another substance. The particles are typically between 1 and 1000 nanometers in diameter.

  2. What are the two phases of a colloid? Solution: A colloid consists of two phases: the dispersed phase, which is the particles or droplets being dispersed, and the dispersion medium, which is the substance in which the dispersed phase is distributed.
  3. Name five types of colloids, based on the states of the dispersed phase and the dispersion medium. Solution: Examples of colloids based on the states of the dispersed phase and the dispersion medium are: solid/liquid (sol), liquid/liquid (emulsion), gas/liquid (foam), liquid/gas (aerosol), and solid/gas (smoke).
  4. What is the Tyndall effect? Solution: The Tyndall effect is the scattering of light by particles in a colloid or a very fine suspension. This makes a beam of light visible as it passes through the colloid.
  5. How are colloids different from solutions and suspensions? Solution: Colloids differ from solutions and suspensions in terms of particle size. In solutions, particles are individual molecules or ions, which are much smaller than those in a colloid. Suspensions contain larger particles that will settle out over time, while the particles in a colloid will not.
  6. What is Brownian motion and what role does it play in colloids? Solution: Brownian motion is the random motion of particles in a fluid (liquid or gas) resulting from their collision with fast-moving molecules in the fluid. This motion prevents the particles in a colloid from settling out.
  7. How can colloids be separated? Solution: Colloids can be separated by techniques such as centrifugation and ultrafiltration, which exploit the size of the colloidal particles.
  8. What are hydrophilic and hydrophobic colloids? Solution: Hydrophilic colloids have particles that are attracted to water, while hydrophobic colloids have particles that repel water.
  9. What is an emulsion? Solution: An emulsion is a type of colloid in which both the dispersed phase and the dispersion medium are liquids. An example is milk, which is a water-based liquid containing dispersed fat droplets.
  10. What is coagulation in the context of colloids? Solution: Coagulation, or flocculation, refers to the process in which the dispersed particles in a colloid aggregate to form larger particle clusters, which can then be separated from the dispersion medium.
  11. What is a colloidal system? Solution: A colloidal system refers to a system in which one substance of microscopically dispersed insoluble particles is suspended throughout another substance.
  12. What role do emulsifiers play in colloidal systems? Solution: Emulsifiers stabilize colloidal systems by reducing the surface tension between the dispersed phase and the dispersion medium. This prevents the dispersed particles from aggregating and separating out.
  13. What is an aerosol? Solution: An aerosol is a type of colloid in which solid particles or liquid droplets are dispersed in a gas.
  14. What are micelles? Solution: Micelles are aggregates of surfactant molecules dispersed in a liquid colloid. They form when the concentration of the surfactant is above the critical micelle concentration (CMC).
  15. Why is milk considered a colloidal system? Solution: Milk is considered a colloidal system because it is composed of butterfat globules dispersed in water, with proteins forming a colloidal solution.
  16. What happens when a colloid undergoes dialysis? Solution: Dialysis of a colloid allows the small ions or molecules to pass through a semipermeable membrane, but the larger colloidal particles cannot pass through.
  17. Why do colloidal particles not settle down under the influence of gravity? Solution: Colloidal particles do not settle under the influence of gravity due to the small size of the particles and the ongoing random movements of particles known as Brownian motion.
  18. What is an example of a natural colloid? Solution: A natural colloid example is blood, which is a colloidal dispersion of blood cells in plasma.
  19. What is meant by the protective action of colloids? Solution: The protective action of colloids refers to their ability to prevent the coagulation of a colloidal system. Certain colloidal particles can absorb ions onto their surface, providing a charge that keeps other particles in the system dispersed.
  20. What is peptization? Solution: Peptization is the process of converting a precipitate into a colloidal solution by shaking it with the dispersion medium in the presence of a small amount of electrolyte. The electrolyte provides a charge on the particles of the precipitate, allowing them to repel each other and become dispersed throughout the medium.

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