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Surface Tension and Interfacial Phenomena Part-2
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Surface Tension and Interfacial Phenomena Part-2

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Questions and Answers

What is the symbol for the surface tension of the spreading liquid?

  • γLS
  • γL (correct)
  • γS
  • Wa

    • What is the work of adhesion (Wa) equal to?

  • 2γL
  • γL + γS - γLS (correct)
  • 2γS
  • γL + γS

    • What is the condition for spreading of oil on a water surface?

  • Wa < Wc
  • Wa > Wc (correct)
  • Wa = Wc
  • Wa = 2γL

    • What is the work of cohesion (Wc) equal to?

    <p>2γL</p> Signup and view all the answers

    What is the symbol for the interfacial tension between the two liquids?

    <p>γLS</p> Signup and view all the answers

    What is the force of attraction between the oil and the water measured by?

    <p>Work of adhesion</p> Signup and view all the answers

    What is the primary function of surfactants?

    <p>To mediate between two phases and decrease the interfacial tension</p> Signup and view all the answers

    What happens to the interfacial tension when more surfactants are added beyond the saturation point?

    <p>It remains constant</p> Signup and view all the answers

    What is the term for the strong interactions between surfactants and both phases?

    <p>Amphiphilic interaction</p> Signup and view all the answers

    What is the purpose of the HLB scale?

    <p>To classify surfactants</p> Signup and view all the answers

    What is the result of micelle formation?

    <p>A decrease in interfacial tension</p> Signup and view all the answers

    How many types of micelles are there?

    <p>Two</p> Signup and view all the answers

    What is the term for the ability of surfactants to form strong interactions with both phases?

    <p>Amphiphilic</p> Signup and view all the answers

    What is the purpose of determining the HLB of a surfactant?

    <p>To determine its effectiveness in a particular application</p> Signup and view all the answers

    What is the term (Wa - Wc) known as?

    <p>Spreading coefficient</p> Signup and view all the answers

    What is the formula for the spreading coefficient S?

    <p>S = Wa - Wc</p> Signup and view all the answers

    What is the characteristic of a surfactant molecule?

    <p>Polar head group and non-polar hydrocarbon chain</p> Signup and view all the answers

    What is the orientation of surfactants at a water surface?

    <p>Head group resides in the water and hydrocarbon chain points to the gaseous phase</p> Signup and view all the answers

    What is the term for the energy difference between a liquid spreading on a surface and a liquid in contact with a second surface?

    <p>Spreading coefficient</p> Signup and view all the answers

    What is the function of the polar head group of a surfactant molecule?

    <p>Forms strong interactions with polar solvents</p> Signup and view all the answers

    What is the function of the non-polar hydrocarbon chain of a surfactant molecule?

    <p>Forms strong interactions with non-polar solvents</p> Signup and view all the answers

    What is the term for compounds that are interfacially active?

    <p>All of the above</p> Signup and view all the answers

    Surfactants can be classified by their structure based on the type of polar group into how many general classes?

    <p>Four</p> Signup and view all the answers

    What is the primary function of a wetting agent?

    <p>Reducing surface tension</p> Signup and view all the answers

    Surfactants are used to increase the solubility of sparingly soluble drugs by which mechanism?

    <p>Micelles formation</p> Signup and view all the answers

    What is the primary function of a detergent agent?

    <p>Cleaning</p> Signup and view all the answers

    Which of the following is NOT a classification of surfactants by application?

    <p>Antibacterial agent</p> Signup and view all the answers

    What is the primary function of a foaming agent?

    <p>Creating foam</p> Signup and view all the answers

    Which of the following is a potential effect of a surfactant on a drug?

    <p>All of the above</p> Signup and view all the answers

    What is the primary function of an emulsifier agent?

    <p>Stabilizing emulsions</p> Signup and view all the answers

    What is the effect of a low concentration of surfactant on the penetration of hexylresorcinol into the pinworm, Ascaris?

    <p>It reduces the interfacial tension between the liquid phase and the cell wall.</p> Signup and view all the answers

    What happens when the concentration of surface-active agent exceeds that required to form micelles?

    <p>The rate of penetration of the anthelmintic decreases nearly to zero.</p> Signup and view all the answers

    What is the mechanism of antibacterial activity of quaternary ammonium compounds?

    <p>They increase the permeability of the lipid cell membrane.</p> Signup and view all the answers

    What is the result of the destruction of bacterial cells by quaternary ammonium compounds?

    <p>Loss of essential materials from the cell.</p> Signup and view all the answers

    What is the function of lung surfactant?

    <p>To decrease the surface tension at the air–alveoli interface.</p> Signup and view all the answers

    What is the first main task of lung surfactant?

    <p>To prevent the collapse of alveoli.</p> Signup and view all the answers

    What is the second main task of lung surfactant?

    <p>To decrease the pressure inside the alveoli.</p> Signup and view all the answers

    What is the consequence of the absence of lung surfactant?

    <p>Pulmonary edema.</p> Signup and view all the answers

    Study Notes

    Surface Tension and Interfacial Phenomena

    • The work of adhesion (Wa) is the energy required to break the attraction between unlike molecules, and it is equal to the newly created surface tensions, γL and γS, minus the interfacial tension, γLS, that has been destroyed in the process.
    • Wa = γL + γS − γLS
    • The work of cohesion (Wc) is the energy required to separate the molecules of the spreading liquid so that it can flow over the sublayer, and it is equal to 2γL.
    • Spreading of oil on a water surface occurs if the work of adhesion (a measure of the force of attraction between the oil and the water) is greater than the work of cohesion.
    • The term (Wa – Wc) is known as the spreading coefficient (S).

    Spreading Coefficient

    • S = Wa − Wc = (γL + γS − γLS) − 2γL
    • S = γS − γL − γLS
    • S = γS − (γL + γLS)

    Surfactants

    • Surfactants are interfacially active compounds that consist of a polar head group and a non-polar hydrocarbon chain.
    • The polar part (hydrophilic) of the molecule can interact strongly with polar solvents, like water.
    • The non-polar part (hydrophobic) can form strong interactions with non-polar solvents, like oil.
    • At an interface, surfactants orient themselves in such a way that the head group resides in the water and the hydrocarbon chain points to the gaseous phase.
    • Surfactants can mediate between two phases as they can form strong interactions with both of them, decreasing the interfacial tension.
    • The decrease of the interfacial tension caused by surfactants becomes stronger the more surfactants are adsorbed at the interface.

    Micelle Formation

    • Mechanisms of micelle formation: a) structure of amphiphilic surfactants, b) surface saturated with amphiphilic surfactants, and c) structure of micelle.
    • There are two types of micelles.

    HLB Scale

    • HLB (Hydrophile–Lipophile Balance) scale is a method for determining the balance between the hydrophilic and lipophilic properties of a surfactant.

    Classification of Surfactants

    • Classification by structure: non-ionic, anionic, cationic, and amphoteric surfactants.
    • Classification by application: wetting agents, foaming agents, emulsifier agents, and detergents agents.

    Applications of Surfactants

    • Increase solubility of sparingly soluble drugs, usually by micelle formation.
    • In addition to the use of surfactants as emulsifying agents, detergents, wetting agents, and solubilizing agents, they find application as antibacterial and other protective agents and as aids to the absorption of drugs in the body.
    • Surfactants can affect the activity of a drug or may themselves exert drug action.
    • Examples of surfactants that possess antibacterial activity include quaternary ammonium compounds, which are adsorbed on the cell surface and supposedly bring about destruction by increasing the permeability or “leakiness” of the lipid cell membrane.
    • Lung surfactant is a surface-active agent that covers the surface of alveoli contacted with air, decreasing the surface tension at the air–alveoli interface almost to zero, and preventing the collapse of alveoli and pulmonary edema.

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    Description

    This quiz covers the concepts of surface tension, interfacial phenomena, and spreading coefficient. It also explores the work of adhesion and its relationship with unlike molecules.

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