Biology Chapter 1: Surface Phenomena
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Questions and Answers

What is the term for the boundary that separates two different phases of matter?

  • Phase line
  • Interface (correct)
  • Boundary layer
  • Surface area

    • Why do polar liquids typically have higher surface tensions than non-polar liquids?

  • They have less viscosity
  • They exhibit stronger hydrogen bonds (correct)
  • They have higher molecular weight
  • They contain fewer molecules

    • What is the equation relating work done to increase surface energy?

  • $dW = eta . dT$
  • $dW = au . dA$
  • $dW = au . dS$ (correct)
  • $dW = ho . dS$

    • What happens during the creation of new surfaces?

    <p>It leads to energy consumption (D)</p> Signup and view all the answers

    In the MKSA system, how is surface tension ($ au$) expressed?

    <p>$N/m$ (B)</p> Signup and view all the answers

    What is the primary factor that causes variations in surface tension among different liquids?

    <p>Strength of intermolecular forces (D)</p> Signup and view all the answers

    If the energy of adhesion is greater than the energy of cohesion, what can be concluded about the wetting of the liquid?

    <p>The liquid will spread, indicating good wetting (C)</p> Signup and view all the answers

    Which equation correctly defines the spreading coefficient (S)?

    <p>S = W_a - W_c (A)</p> Signup and view all the answers

    What does it indicate if the spreading coefficient (S) is less than zero?

    <p>Poor wetting occurs (A)</p> Signup and view all the answers

    What term is used to describe the attraction between molecules of the same substance?

    <p>Cohesion (B)</p> Signup and view all the answers

    In the equation $W_a = \sigma_L (1 + cos \theta)$, what does $\theta$ represent?

    <p>Angle of contact (B)</p> Signup and view all the answers

    What is the unit of work of cohesion ($W_c$) expressed in the context given?

    <p>Erg per centimeter squared (erg/cm²) (B)</p> Signup and view all the answers

    Which of the following describes a condition of good wetting?

    <p>The spreading coefficient is greater than zero (C)</p> Signup and view all the answers

    What effect does a higher surface tension have on a liquid in a tube according to Jurin's Law?

    <p>It allows the liquid to rise higher in the tube. (C)</p> Signup and view all the answers

    In the context of alveoli, what occurs when smaller alveoli collapse into larger ones?

    <p>Air flows from the smaller alveoli to the larger alveoli. (D)</p> Signup and view all the answers

    What happens to the height of the liquid in a non-wettable tube?

    <p>The height is described as negative. (D)</p> Signup and view all the answers

    Which statement correctly describes the nature of emulsions?

    <p>Emulsions are a dispersion of one liquid in another immiscible liquid. (C)</p> Signup and view all the answers

    How does the radius of the tube influence the height of the liquid according to Jurin's Law?

    <p>The height decreases as the radius increases. (C)</p> Signup and view all the answers

    What is the primary role of surfactants in emulsions?

    <p>To reduce the surface tension between phases. (A)</p> Signup and view all the answers

    What results when the angle θ is greater than π/2 in terms of the liquid's behavior in a tube?

    <p>The liquid falls. (B)</p> Signup and view all the answers

    What must occur to effectively create a foam?

    <p>A gas must be vigorously agitated with a liquid. (A)</p> Signup and view all the answers

    What is the shape of the surface tension for a soap bubble?

    <p>4σ (D)</p> Signup and view all the answers

    How does increasing liquid density (ρ) affect the height (h) in a capillary tube?

    <p>The height decreases. (A)</p> Signup and view all the answers

    Flashcards

    Interface

    The boundary between two different phases of matter, like solid-liquid, liquid-gas, or solid-gas.

    Surface Tension

    The energy required to create a new surface. It's a measure of the force acting per unit length on the surface of a liquid.

    Surface Energy

    The inherent energy associated with a surface. It increases when a new surface is created.

    Surface Tension Units

    A measure of the force acting per unit length on the surface of a liquid. It is usually expressed in units of Newtons per meter (N/m) or dynes per centimeter (dyne/cm).

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    Water's High Surface Tension

    Water has a high surface tension due to the strong hydrogen bonds between its molecules, which exert a strong cohesive force.

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    Cohesion

    The attraction between molecules of the same substance.

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    Adhesion

    The attraction between molecules of different substances.

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    Cohesion Work (WC)

    The work required to separate two surfaces of a liquid by a unit area.

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    Adhesion Work (Wa)

    The work required to separate a liquid from a solid surface by a unit length.

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    Spreading Coefficient (S)

    A measure of the tendency of a liquid to spread across a solid surface.

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    Condition for Wetting

    Spreading occurs when the energy of adhesion (Wa) is greater than the energy of cohesion (Wc).

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    Contact Angle (ϴ)

    The angle between a liquid droplet and a solid surface. It indicates the degree of wetting.

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    Overpressure inside a droplet

    The difference in pressure between the inside and outside of a droplet.

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    Laplace Pressure

    The pressure difference across a curved surface due to surface tension.

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    Surface Tension (σ)

    The force exerted on a liquid surface per unit length.

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    Capillary Rise (h)

    The height to which a liquid rises in a narrow tube due to surface tension.

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    Perfect Wetting

    A liquid completely wets a solid surface when the contact angle is zero degrees.

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    Non-Wetting

    A liquid doesn't wet a solid surface when the contact angle is 180 degrees.

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    Surface Tension Driven Collapse of Smaller Alveoli

    The tendency of smaller bubbles or cavities to collapse into larger ones due to surface tension.

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    Emulsion

    A dispersion of microscopic droplets of one liquid in another immiscible liquid.

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    Foam

    A dispersion of gas bubbles within a liquid.

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    Study Notes

    Chapter 01: Surface Phenomena

    • Surface phenomena play a significant role in biological systems, acting as sites of intense molecular activity.
    • Cellular surfaces are crucial for metabolic processes.
    • Creation of new surfaces consumes energy.
    • An interface is the boundary where two different phases of matter meet (e.g., solid-liquid, liquid-gas, solid-gas).

    Surface Tension

    • Surface tension (σ) is the energy required to increase the surface area of a liquid.
    • Units for surface tension:
      • MKSA system: J/m²
      • CGSA system: erg/cm²
      • 1 dyne = 10⁻⁵ N
      • 1 erg = 10⁻⁷ J
    • Bringing a molecule from the bulk to the surface requires work, increasing surface energy.
    • Work (dW) = σ * dS (where dS is change in surface area)

    Intermolecular Forces and Surface Tension

    • Water has a high surface tension due to strong hydrogen bonding.
    • Polar liquids have higher surface tensions than nonpolar liquids because of stronger intermolecular forces.
    • Surface tension varies considerably between liquids based on intermolecular attractions.

    Adhesion and Cohesion

    • Adhesion: The attraction between molecules of different substances.
    • Cohesion: The attraction between molecules of the same substance.
    • These forces impact wetting characteristics.

    Wetting

    • Wetting describes how a liquid interacts with a surface.
    • Contact angle (θ): The angle formed by the liquid-air interface and the solid-liquid interface.
    • θ < 90°: Good wetting
    • θ > 90°: Poor wetting
    • θ = 180°: Non-wetting
    • θ = 0°: Complete wetting

    Spreading Coefficient (S)

    • The spreading coefficient determines if a liquid spreads on a surface.
    • S = Wa - Wc (where Wa is the adhesion work and Wc is the cohesion work)
    • S > 0: Good wetting (liquid spreads)
    • S < 0: Poor wetting (liquid doesn't spread)

    Overpressure in Droplets and Bubbles

    • Overpressure (ΔP) exists inside liquid droplets and bubbles, related to surface tension and radius.
    • Spherical surface: ΔP = 2σ/R
    • Cylindrical surface: ΔP = σ/R
    • Soap bubble: ΔP = 4σ/r
    • ΔP accounts for differences in pressure between the interior and exterior of a surface.
    • Jurin's Law describes how liquid height in a capillary tube is related to surface tension and radius. Higher surface tension and smaller radius leads to higher liquid column in the tube.

    Surfactants

    • Surfactants reduce surface tension at the surface of alveoli in the lungs.
    • Alveoli are better able to resist collapse with sufficient surfactant levels.

    Foams & Emulsions

    • Foams: Dispersions of gas in liquid, created by vigorous agitation.
    • Emulsions: Dispersions of one liquid in another immiscible liquid. Surfactants stabilize emulsions by reducing interfacial tension and creating protective layers.

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    Chapter 01 - Surface Phenomena (2024-2025) - PDF

    Description

    Explore the critical role of surface phenomena in biological systems. This quiz covers topics like surface tension, energy requirements for creating new surfaces, and the impact of intermolecular forces on surface tension. Understand these concepts to grasp their significance in metabolic processes.

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