test flashcards

All 20 cards

1. Card 1

   Define 'dispersed phase' and 'dispersed medium' in the context of colloidal dispersions.

   The dispersed phase is the substance (solid, liquid, or gas) distributed in the dispersed medium in the form of colloidal particles. The dispersed medium, also known as the continuous phase, is the liquid, gas, or solid in which the dispersed phase is distributed.

2. Card 2

   How do fine dispersions, colloidal dispersions, and roughly dispersed mixtures differ based on particle size?

   Fine dispersions have particles smaller than 1 nanometer, making them homogeneous mixtures. Colloidal dispersions have particle sizes ranging from 1 to 1000 nanometers and are micro-heterogeneous mixtures. Roughly dispersed mixtures have particles larger than 1000 nanometers and are heterogeneous mixtures or suspensions.

3. Card 3

   Explain how the visibility of particles distinguishes homogeneous, colloidal, and heterogeneous mixtures.

   Homogeneous mixtures are not visible under light or electron microscopes. Colloidal dispersions can be distinguished using microscopes, ultracentrifugation, or ultrafiltration. Heterogeneous mixtures have particles visible to the naked eye, with filter papers, or normal microscopes, and can be separated by centrifugation or gravity.

4. Card 4

   Describe the principle behind ultrafiltration as a method for separating colloidal particles.

   Ultrafiltration utilizes a special membrane along with a pressure or concentration gradient to separate the dispersed medium from the colloidal particles. This method effectively separates components based on their size difference.

5. Card 5

   What is dialysis and what is its purpose in separating components from a mixture?

   Dialysis is a process used to separate suspended colloidal particles from dissolved ions or molecules of small dimensions (crystalloids). It achieves this separation by exploiting the unequal rates of diffusion of these substances through the pores of a semipermeable membrane.

6. Card 6

   Classify macromolecular colloids, associative colloids, and dispersion colloids based on their chemical nature, providing an example for each.

   Macromolecular colloids consist of large molecules like proteins or polymers. Associative colloids are formed by grouped amphipathic molecules or ions, such as micelles (soap/detergents) or vesicles. Dispersion colloids are formed by grinding or condensing particles, like emulsions (oils) or metals.

7. Card 7

   Distinguish between lyophilic and lyophobic colloids based on their affinity towards the dispersion medium.

   Lyophilic colloids have a strong affinity for the dispersion medium (e.g., water), meaning they are hydrophilic and/or hydrophobic. Lyophobic colloids have a weak affinity for the dispersion medium (e.g., water), being either hydrophobic or hydrophilic.

8. Card 8

   Provide an example of an emulsion and a colloidal sol, specifying the dispersed phase and dispersed medium for each.

   Milk is an example of an emulsion where the dispersed phase is liquid and the dispersed medium is also liquid. Colloidal sols, such as rocks in water, have a solid dispersed phase within a liquid dispersed medium.

9. Card 9

   Explain the Tyndall's effect and how it demonstrates the presence of colloidal particles.

   The Tyndall's effect describes the scattering of UV or visible light as it passes through a colloidal dispersion system. The light is reflected off the surface of the colloidal particles, making the light beam visible, which proves the mixture is heterogeneous despite appearing homogeneous to the naked eye.

10. Card 10

    What is Brownian motion and how does it characterize colloidal particles?

    Brownian motion refers to the random and straightforward movement of colloidal particles within the dispersion medium. This continuous, erratic motion is a characteristic property of colloids, resulting from collisions with molecules of the dispersion medium.

11. Card 11

    How does high surface energy relate to the properties of colloidal particles, particularly hydrophobic colloids?

    Colloidal particles possess high surface energy, which increases as particle size decreases and the degree of dispersion increases. This excess energy at the surface is particularly significant for hydrophobic colloids, influencing their interactions and stability.

12. Card 12

    Define adsorption and explain its effect on colloidal particles.

    Adsorption is the spontaneous accumulation of a substance (adsorbate) onto the surface of another substance (adsorbent). This physical process increases the size of the colloidal particle and lowers its surface energy, which is an exothermic process leading to a decrease in entropy.

13. Card 13

    Describe the electric double layer surrounding colloidal particles in a dispersive medium.

    In a dispersive medium, colloidal particles develop an electric double layer due to strong ionic interactions with oppositely charged ions in the medium. This layer consists of a stationary layer directly interacting with the particle and a diffuse layer further away, mildly attracted to the particle within the solution.

14. Card 14

    Why are oil-in-water emulsions considered thermodynamically unstable systems?

    Oil-in-water emulsions are thermodynamically unstable due to the high surface energy of the oil particles relative to their mass. The hydrophobic nature of oil leads to weak interactions with the aqueous medium, making them prone to separation unless emulsifiers are present to reduce surface energy and stabilize the system.

15. Card 15

    Explain why micelles are considered thermodynamically stable colloidal systems in aqueous media.

    Micelles are stable colloidal systems because they are single-layered particles with a non-polar interior, formed by amphipathic molecules like soap or detergents. In aqueous media, their hydrophilic exterior results in a total negative charge, which contributes to their stability and prevents aggregation.

16. Card 16

    How do proteins achieve thermodynamic stability in water, and what prevents their coagulation?

    Proteins are thermodynamically stable in water because they ionize as polyelectrolytes. They form a hydration shell around their particles, which prevents coagulation by causing repulsion between the particles, thus maintaining their dispersed state.

17. Card 17

    What is the role of an emulsifier in preparing a thermodynamically stable colloidal system like an oil-in-water emulsion?

    An emulsifier, composed of amphipathic molecules or ions, forms a polar exterior and a nonpolar interior around oil droplets. This structure allows the oil to be surrounded and mixed with water, reducing the surface energy of the oil particles and creating stronger intermolecular forces between oil and water, thus stabilizing the emulsion.

18. Card 18

    Define peptization and its significance in forming stable hydrophobic colloidal sols.

    Peptization is the process of forming a stable hydrophobic colloidal sol (solid in liquid) by washing solid particles with an electrolyte solution (acids, bases, or salts). This process helps to disperse the solid particles into a stable colloidal state by preventing their aggregation.

19. Card 19

    Describe the process of protein coagulation, including the role of dehydrating agents.

    Protein coagulation occurs when a dehydrating agent, such as ethanol, is added to the system. The alcohol disrupts the interaction between the electrolyte (proteins) and water, leading to the formation of a heterogeneous system with a smaller total surface area relative to the total mass of the accumulated particles.

20. Card 20

    Explain the basis of electrophoresis as a separation method for mixtures of different colloidal particles.

    Electrophoresis separates different colloidal particles in the same medium based on their varying total charges, shapes, and sizes. When an electric field is applied, particles with different properties will move at different speeds, allowing for their effective separation within the medium.

More flashcard decks

• unit test 1 flashcards (37 cards)
• IT certification test flashcards (20 cards)
• Thermochemistry and Thermodynamics flashcards (149 cards)
• Género Bacillus y Clostridium flashcards (100 cards)
• Ψηφιακά Παιχνίδια και Μάθηση flashcards (100 cards)
• Philosophy AS flashcards (100 cards)

Browse every shared deck