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Questions and Answers
What defines an interface between two phases?
What defines an interface between two phases?
Which of the following best describes surface tension?
Which of the following best describes surface tension?
What is one key role of surface active agents in the body?
What is one key role of surface active agents in the body?
Which scenario would result in a lack of interfacial tension?
Which scenario would result in a lack of interfacial tension?
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How does surface tension influence the shape of liquid droplets?
How does surface tension influence the shape of liquid droplets?
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What is the primary reason that interfacial tension is often less than surface tension?
What is the primary reason that interfacial tension is often less than surface tension?
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In the context of surface and interfacial tension, what is a dyne?
In the context of surface and interfacial tension, what is a dyne?
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What effect does increasing the length of a liquid surface have on surface tension?
What effect does increasing the length of a liquid surface have on surface tension?
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What role do functional groups on the surface of a solid play in relation to adsorbate molecules?
What role do functional groups on the surface of a solid play in relation to adsorbate molecules?
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What effect does a wetting agent have on the contact angle?
What effect does a wetting agent have on the contact angle?
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Which of the following describes the composition of the tightly bound layer in the electric double layer?
Which of the following describes the composition of the tightly bound layer in the electric double layer?
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What is zeta potential an indicator of?
What is zeta potential an indicator of?
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Which process can result in particles obtaining a charge when dispersed in a liquid medium?
Which process can result in particles obtaining a charge when dispersed in a liquid medium?
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What does the symbol $γ$ represent in the equation $γ = \frac{F_b}{2L}$?
What does the symbol $γ$ represent in the equation $γ = \frac{F_b}{2L}$?
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What happens to the pressure difference ($ΔP$) in a soap bubble as the radius ($r$) increases?
What happens to the pressure difference ($ΔP$) in a soap bubble as the radius ($r$) increases?
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Which method is specified for the determination of surface tension only?
Which method is specified for the determination of surface tension only?
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How does the surface tension of water change as temperature increases?
How does the surface tension of water change as temperature increases?
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In the equation for work done, $dW=F*ds= γ 2Lds$, what does $dW$ represent?
In the equation for work done, $dW=F*ds= γ 2Lds$, what does $dW$ represent?
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What happens to the surface tension of water at 75˚C compared to its surface tension at 0˚C?
What happens to the surface tension of water at 75˚C compared to its surface tension at 0˚C?
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What is the equation that expresses the relationship between pressure difference and the radius of a bubble?
What is the equation that expresses the relationship between pressure difference and the radius of a bubble?
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Which method is NOT suitable for interfacial tension determination?
Which method is NOT suitable for interfacial tension determination?
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Which surfactant is completely miscible with water and has no effect at the interface?
Which surfactant is completely miscible with water and has no effect at the interface?
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What does a higher HLB value indicate about a surfactant?
What does a higher HLB value indicate about a surfactant?
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What is required HLB (RHLB) primarily used for?
What is required HLB (RHLB) primarily used for?
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In the mixture containing Tween 80 and Span 80, what percentage of the surfactant is Span 80?
In the mixture containing Tween 80 and Span 80, what percentage of the surfactant is Span 80?
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What characterizes amphiphilic molecules?
What characterizes amphiphilic molecules?
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What is the basis for calculating the Required HLB (RHLB) for a mixture of oily materials?
What is the basis for calculating the Required HLB (RHLB) for a mixture of oily materials?
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How is surface excess or surface concentration (Γ) defined?
How is surface excess or surface concentration (Γ) defined?
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Which of the following statements regarding insoluble films is correct?
Which of the following statements regarding insoluble films is correct?
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What is the primary factor causing the rise of liquid in a capillary tube?
What is the primary factor causing the rise of liquid in a capillary tube?
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Which formula represents the equilibrium condition when a liquid rises in a capillary tube?
Which formula represents the equilibrium condition when a liquid rises in a capillary tube?
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What does a positive spreading coefficient, S, indicate?
What does a positive spreading coefficient, S, indicate?
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In the DuNouy ring method, what does the force reading measure?
In the DuNouy ring method, what does the force reading measure?
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What property of surfactants allows them to accumulate at liquid interfaces?
What property of surfactants allows them to accumulate at liquid interfaces?
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Under what conditions does spreading occur between two liquids?
Under what conditions does spreading occur between two liquids?
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What role does the radius of the capillary play in the liquid's height in the capillary tube?
What role does the radius of the capillary play in the liquid's height in the capillary tube?
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Which factor does NOT affect the spreading of a liquid on the surface of water?
Which factor does NOT affect the spreading of a liquid on the surface of water?
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What does the film thickness formed by oils on water surface represent?
What does the film thickness formed by oils on water surface represent?
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What is surface or film pressure, π, defined as?
What is surface or film pressure, π, defined as?
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What factors affect the degree of gas adsorption on a solid surface?
What factors affect the degree of gas adsorption on a solid surface?
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What is the difference between physical sorption and chemi-sorption?
What is the difference between physical sorption and chemi-sorption?
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Which equation is often used to describe adsorption isotherms?
Which equation is often used to describe adsorption isotherms?
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What does the term 'desorption' refer to in the context of adsorption?
What does the term 'desorption' refer to in the context of adsorption?
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What role does activated charcoal play in relation to poisoning?
What role does activated charcoal play in relation to poisoning?
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What does an adsorption isotherm plot represent?
What does an adsorption isotherm plot represent?
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Study Notes
Interfacial Phenomena
- An interface is the boundary between phases.
- Properties of interface molecules differ from bulk molecules.
- Interface type depends on adjacent phase states.
- "Surface" refers to gas-liquid or gas-solid interfaces.
Classification of Interfaces
- Gas-Gas: No interface possible.
- Gas-Liquid: YLV (liquid surface)
- Gas-Solid: Ysv (solid surface)
- Liquid-Liquid: YLL (liquid-liquid interface)
- Liquid-Solid: YLS (liquid-solid interface)
- Solid-Solid: Yss (solid-solid interface, touching particles)
Importance of Interfacial Phenomena
- Drug absorption and penetration through membranes.
- Emulsion and suspension stability.
- Surface-active agent function (e.g., in lungs).
Liquid Interfaces
- Liquid-gas
- Liquid-liquid
- Liquid-solid
Surface and Interfacial Tension
- Cohesive forces act between similar molecules.
- Adhesive forces act between dissimilar molecules.
- Interfacial tension results from the unsimilarity of bulk and interface forces.
- Liquid droplets are spherical due to minimizing surface area.
Surface and Interfacial Tension Units
- Force per unit length (dyne/cm or Newton/meter)
- 1 Newton = 100,000 dynes
- 1 dyne = 0.00001 Newton
Interfacial Tension Compared to Surface Tension
- Interfacial tensions are usually lower than surface tensions due to adhesive forces.
- Miscible liquids have no interfacial tension.
Measurement of Surface and Interfacial Tension
- Capillary rise method (for surface tension—not interfacial)
- Du Noüy ring method
- Drop weight method
- Bubble pressure method
- All experiments should be performed at constant temperature.
Capillary Rise Method
- Liquid rises in a capillary due to adhesive and wetting forces.
- Depends on surface tension, liquid density, and capillary radius.
- Rise continues until upward force equals downward gravity force.(upward force= down ward force)
Surface Tension and Bubbles
- Young-Laplace equation: ΔP = 2γ/r ( ΔP is pressure difference, γ is surface tension, and r is radius)
- Pressure inside a curved surface is higher than outside.
Effect of Temperature
- Surface tension of most liquids decreases with increasing temperature.
Adsorption at Liquid Interfaces
- Adsorption occurs at liquid surfaces where molecules prefer the surface.
- Surface-active agents, or surfactants, exhibit this preference.
Surfactant Molecules
- Amphiphilic molecules (polar and nonpolar parts)
- Polar (hydrophilic): Water-loving
- Nonpolar (lipophilic): Oil-loving
Hydrophilic-Lipophilic Balance (HLB)
- Classification system for surfactants based on their optimum use.
- Higher HLB values = more hydrophilic.
- Lower HLB values = more lipophilic.
Types of Monolayers at Liquid Surfaces
- Soluble monolayers (e.g., amyl alcohol in water—dissolves)
- Insoluble films (e.g., cetyl alcohol in water—does not dissolve)
- Surface excess (Γ) is amount of surfactant per unit surface area exceeding the bulk
Adsorption Isotherms
- Isotherms are plots showing the relationship between adsorbed amount and partial pressure at a constant temperature.
Adsorption of Gases on Solids
- Adsorption degree depends on adsorbent and adsorbate chemical nature, surface area, partial pressure, and temperature.
- Desorption is adsorbate removal from surface via elevating temperature or reducing pressure.
- Physical sorption and chemical sorption (reversible/irreversible).
Adsorption at Solid-Liquid Interfaces
- Solutes from solutions adsorb onto solid surfaces (e.g., charcoal).
- Similar to solid-gas isotherms.
- Langmuir equation can be used (C/(x/m) = 1/(Ym b) + C/ Ym)
Activated Charcoal
- Used as antidote for poisoning.
- High surface area (e.g., 3000 m²/g)
- Surface functional groups facilitate adsorbate molecule bonding.
- Adsorption of gases on solid materials
Wetting
- Contact angle: Angle between liquid and solid surface
- Wetting agent: surfactant that lowers the contact angle.
Electric Properties of Interfaces
- Particles in liquid media can gain a charge due to selective adsorption, ionization of surface groups, or differences in dielectric constants.
Electric Double Layer
- Tightly bound layer contains less counter ion charge than the adsorbed layer.
- Diffuse layer has more negative charge; equal negative and positive charges.
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Description
Explore the fascinating world of interfacial phenomena and learn about the properties of molecules at the interface between different phases. This quiz covers various types of interfaces, their classifications, and the significance of interfacial tension in real-world applications such as drug absorption and emulsion stability.
