Interfacial Phenomena in Liquids
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Questions and Answers

What is the net effect of the forces experienced by molecules at the surface of the liquid?

  • An upward force away from the liquid
  • An outward force towards the interface
  • An inward force toward the bulk (correct)
  • A downward force into the liquid

    • What is interfacial tension?

  • The force per unit volume at the interface between a liquid and a gas phase
  • The force per unit area at the interface between two immiscible liquid phases
  • The force per unit mass at the interface between two miscible liquid phases
  • The force per unit length at the interface between two immiscible liquid phases (correct)

    • Why are interfacial tensions generally less than surface tensions?

  • Because interfacial tensions have units of dynes/cm
  • Because surface tension is not present in interfacial tensions
  • Because cohesive forces between molecules are stronger at the interface
  • Because adhesive forces between two liquid phases are smaller than between a liquid and a gas phase (correct)

    • Why do micelles form when more surface active agent is added to water?

    <p>To protect their hydrophobic groups from the aqueous environment</p> Signup and view all the answers

    What happens to the solubility of a drug when the concentration of the surface active agent increases beyond the CMC concentration?

    <p>The solubility increases sharply</p> Signup and view all the answers

    What does a higher HLB number indicate about a surfactant?

    <p>It is more hydrophilic and acts as a solubilizing agent or detergent</p> Signup and view all the answers

    How do particles dispersed in water acquire a negative charge?

    <p>Due to preferential adsorption of the hydroxyl ion</p> Signup and view all the answers

    What is the main reason for particles dispersed in water to acquire a negative charge?

    <p>Greater tendency of hydroxyl ion to be adsorbed at the surface of particle</p> Signup and view all the answers

    What is the source of charges on particles dispersed in liquid media?

    <p>Ionization of groups at the surface of the particle</p> Signup and view all the answers

    How do cationic quaternary compounds affect gram-negative and gram-positive organisms?

    <p>They are effective against both gram-negative and gram-positive organisms</p> Signup and view all the answers

    What is the net charge of the protein at its isoelectric point?

    <p>Zero net charge</p> Signup and view all the answers

    What happens to the protein at low pH?

    <p>It has a positive charge</p> Signup and view all the answers

    What is the term for the specific pH at which a protein exists as a Zwitterion?

    <p>Isoelectric point</p> Signup and view all the answers

    What happens to the protein at high pH?

    <p>It has a negative charge</p> Signup and view all the answers

    What causes anions to be attracted to a positively charged surface in a polar solution?

    <p>Thermal motion</p> Signup and view all the answers

    What leads to the formation of micelles in the bulk when more surface active agent is added to water?

    <p>Saturated surface with surface active molecules</p> Signup and view all the answers

    Why do micelles form when more surface active agent is added to water?

    <p>To protect their hydrophobic groups from the aqueous environment</p> Signup and view all the answers

    What does the hydrophile–lipophile balance (HLB) number measure in a surfactant?

    <p>Balance between hydrophilic and hydrophobic portions</p> Signup and view all the answers

    What is the impact of a higher HLB number on a surfactant's function?

    <p>Act as solubilizing agents, detergents, and oil-in-water emulsifiers</p> Signup and view all the answers

    What happens to the solubility of a drug when the concentration of the surface active agent increases beyond the CMC concentration?

    <p>The ability to solubilize a drug increases sharply</p> Signup and view all the answers

    How do particles dispersed in water mainly acquire a negative charge?

    <p>Selective adsorption of the hydroxyl ion due to its less hydration</p> Signup and view all the answers

    What leads to the selective adsorption of the hydroxyl ion onto particles dispersed in water?

    <p>Less hydration of the hydroxyl ion compared to the hydronium ion</p> Signup and view all the answers

    What is the primary source of charges on particles dispersed in liquid media?

    <p>Ionization of groups at the surface of the particle</p> Signup and view all the answers

    What is responsible for the charges on particles dispersed in liquid media being a function of pH and pKa?

    <p>Ionization of groups at the particle surface</p> Signup and view all the answers

    How do cationic quaternary compounds affect gram-negative and gram-positive organisms?

    <p>They are effective against both gram-negative and gram-positive organisms</p> Signup and view all the answers

    Study Notes

    Forces at Liquid Surface

    • Molecules at the surface experience net inward forces, leading to minimized surface area.
    • Surface tension results from cohesive forces between liquid molecules.

    Interfacial Tension

    • Interfacial tension is the force at the interface between two different phases, such as liquid-liquid or liquid-gas.
    • It is generally lower than surface tension due to differing intermolecular interactions.

    Formation of Micelles

    • Micelles form when excess surface-active agents aggregate in solution, minimizing energy by sequestering hydrophobic tails.
    • Above the critical micelle concentration (CMC), solubility of certain drugs decreases due to saturation of surfactant.

    HLB Number Significance

    • A higher hydrophile-lipophile balance (HLB) number indicates a more hydrophilic surfactant, which is generally used for oil-in-water emulsions.
    • An HLB number helps tailor surfactants to specific applications based on desired interactions.

    Charge Acquisition in Dispersed Particles

    • Particles dispersed in water mainly acquire a negative charge through selective adsorption of ions, particularly hydroxyl ions (OH⁻).
    • The main source of charges is surface functional groups interacting with ions in the solvent.

    Protein Behavior with pH

    • At the isoelectric point, the net charge of protein is zero, and it precipitates out of solution.
    • Low pH makes proteins positively charged, leading to solubility.
    • At high pH, proteins tend to acquire negative charges and can become less soluble.

    Micelles and Surfactants

    • Micelle formation occurs in bulk when hydrophobic portions of surfactants aggregate, reducing surface energy.
    • Selective adsorption of hydroxyl ions enhances negative charges on particle surfaces.

    Impact of Cationic Compounds

    • Cationic quaternary compounds can disrupt cell membranes of gram-negative and gram-positive organisms, affecting their viability.

    pH and ion Influence on Particles

    • The charges on particles in liquid media are dependent on pH due to equilibrium of acid-base dissociation affecting surface charge density.
    • The dynamic nature of charges is influenced by the pKa of functional groups present on particles.

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    Related Documents

    Chapter 15 Interfacial Phenomena PDF

    Description

    Explore the characteristics of interfacial phenomena in liquids, including the differences in cohesive and adhesive forces experienced by molecules at the bulk and surface of the liquid. This quiz delves into Chapter 15 of interfacial phenomena.

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