Podcast
Questions and Answers
What effect do soaps and detergents have on surface tension?
What effect do soaps and detergents have on surface tension?
Which substance listed has the highest surface tension at 25°C?
Which substance listed has the highest surface tension at 25°C?
How does the presence of impurities affect surface tension?
How does the presence of impurities affect surface tension?
What characteristic do hydrophobic substances display in a liquid?
What characteristic do hydrophobic substances display in a liquid?
Signup and view all the answers
At 25°C, which substance has a surface tension closest to that of octanol?
At 25°C, which substance has a surface tension closest to that of octanol?
Signup and view all the answers
What is the primary reason surface molecules experience a net inward pull?
What is the primary reason surface molecules experience a net inward pull?
Signup and view all the answers
What does surface tension define regarding force on a surface?
What does surface tension define regarding force on a surface?
Signup and view all the answers
What is the typical lifetime of a molecule at the surface before it enters the bulk?
What is the typical lifetime of a molecule at the surface before it enters the bulk?
Signup and view all the answers
What happens to the surface tension of water as temperature increases?
What happens to the surface tension of water as temperature increases?
Signup and view all the answers
Which of the following statements is true about surface free energy?
Which of the following statements is true about surface free energy?
Signup and view all the answers
At what temperature is the surface tension of water approximately 72 mN m-1?
At what temperature is the surface tension of water approximately 72 mN m-1?
Signup and view all the answers
What effect does higher temperature have on water's cleaning capability?
What effect does higher temperature have on water's cleaning capability?
Signup and view all the answers
What is the relationship between surface tension and surface free energy?
What is the relationship between surface tension and surface free energy?
Signup and view all the answers
What is defined as the transition region where two immiscible phases contact each other?
What is defined as the transition region where two immiscible phases contact each other?
Signup and view all the answers
What type of interface exists between two liquids?
What type of interface exists between two liquids?
Signup and view all the answers
What occurs to reduce the energy at the surface of a liquid?
What occurs to reduce the energy at the surface of a liquid?
Signup and view all the answers
How can the surface free energy of a solid be increased?
How can the surface free energy of a solid be increased?
Signup and view all the answers
What is a consequence of having higher surface area in solids?
What is a consequence of having higher surface area in solids?
Signup and view all the answers
What happens to surface molecules compared to those in the bulk?
What happens to surface molecules compared to those in the bulk?
Signup and view all the answers
Which of the following describes the energy needed to increase the surface area of a solid or liquid?
Which of the following describes the energy needed to increase the surface area of a solid or liquid?
Signup and view all the answers
Surface tension occurs in which type of interface?
Surface tension occurs in which type of interface?
Signup and view all the answers
What does the du Nouy tensiometer primarily measure?
What does the du Nouy tensiometer primarily measure?
Signup and view all the answers
What is the formula for calculating the detachment force using the du Nouy tensiometer?
What is the formula for calculating the detachment force using the du Nouy tensiometer?
Signup and view all the answers
What structural characteristic makes surfactants amphipathic?
What structural characteristic makes surfactants amphipathic?
Signup and view all the answers
What is the significance of Traube’s rule in the context of surfactants?
What is the significance of Traube’s rule in the context of surfactants?
Signup and view all the answers
In the structure of surfactants, what does the hydrophobic group typically consist of?
In the structure of surfactants, what does the hydrophobic group typically consist of?
Signup and view all the answers
What must be true regarding the contact angle when using the du Nouy tensiometer for accurate measurements?
What must be true regarding the contact angle when using the du Nouy tensiometer for accurate measurements?
Signup and view all the answers
What happens to surfactants in solution in relation to their structural components?
What happens to surfactants in solution in relation to their structural components?
Signup and view all the answers
What effect does a longer hydrocarbon chain have on surfactant behavior?
What effect does a longer hydrocarbon chain have on surfactant behavior?
Signup and view all the answers
What happens to surface tension when surfactants replace water molecules?
What happens to surface tension when surfactants replace water molecules?
Signup and view all the answers
Which of the following is a characteristic of emulsions?
Which of the following is a characteristic of emulsions?
Signup and view all the answers
How does the addition of surfactants affect the stability of an oil-in-water emulsion?
How does the addition of surfactants affect the stability of an oil-in-water emulsion?
Signup and view all the answers
What contributes to the spontaneous separation of oil and water in a liquid paraffin-water emulsion?
What contributes to the spontaneous separation of oil and water in a liquid paraffin-water emulsion?
Signup and view all the answers
What is the result of shaking an oil-in-water emulsion?
What is the result of shaking an oil-in-water emulsion?
Signup and view all the answers
Which statement about surfactants is correct?
Which statement about surfactants is correct?
Signup and view all the answers
What is the effect of adding sodium dodecyl sulphate to a water-in-oil emulsion?
What is the effect of adding sodium dodecyl sulphate to a water-in-oil emulsion?
Signup and view all the answers
Why is the water-water attractive force significant in emulsion stability?
Why is the water-water attractive force significant in emulsion stability?
Signup and view all the answers
What is the relationship between contact angle (θ) and wetting of a surface?
What is the relationship between contact angle (θ) and wetting of a surface?
Signup and view all the answers
What is the purpose of using a Wilhelmy Plate in surface tension measurement?
What is the purpose of using a Wilhelmy Plate in surface tension measurement?
Signup and view all the answers
In calculating surface tension using the Wilhelmy Plate method, what must be ensured?
In calculating surface tension using the Wilhelmy Plate method, what must be ensured?
Signup and view all the answers
What does the equation γl/v = F/P represent in the context of the Wilhelmy Plate?
What does the equation γl/v = F/P represent in the context of the Wilhelmy Plate?
Signup and view all the answers
How is the perimeter (P) of the Wilhelmy Plate relevant in calculations?
How is the perimeter (P) of the Wilhelmy Plate relevant in calculations?
Signup and view all the answers
In the calculation example provided, what is the surface tension of liquid A at 200C?
In the calculation example provided, what is the surface tension of liquid A at 200C?
Signup and view all the answers
What is a condition for the Wilhelmy Plate to function accurately in static mode?
What is a condition for the Wilhelmy Plate to function accurately in static mode?
Signup and view all the answers
Why is the Wilhelmy Plate method referred to as an absolute method?
Why is the Wilhelmy Plate method referred to as an absolute method?
Signup and view all the answers
Study Notes
MPharm Programme: Surface Tension & Surfactants
- Surface tension is a property of liquids at their interface with a gas, where the liquid-gas interface acts like a skin. A similar concept, interfacial tension, applies where both phases are liquids.
- Surface tension arises from cohesive forces between liquid molecules, pulling them inwards. Surface molecules experience a net downward pull, which leads to a tendency for the surface to contract.
- Surface molecules have more energy than molecules in the bulk of the liquid, due to their differing interactions with neighbouring molecules.
- The energy needed to increase liquid surface area is called surface free energy.
- Water droplets assume a spherical shape due to the minimizing of surface area.
- Larger surface areas in solids (e.g., fine powders) create more free energy, making them more reactive.
- Increasing surface area in solids or liquids demands energy input.
- Surface tension is the force acting parallel to the surface, perpendicular to a one-meter line on the surface. It's numerically equivalent to surface free energy.
- Surface tension of water (25°C) is 72 mN m⁻¹ and declines with increasing temperatures. This impacts pore/fissure penetration in cleaning agents (hot water is more effective than cold).
- Surfactants are amphipathic molecules, combining hydrophobic (water-repelling) and hydrophilic (water-attracting) regions.
- Surfactants lower surface/interfacial tension by adsorbing at interfaces. Hydrophobic tails protrude away from the aqueous phase, while hydrophilic heads engage with the aqueous phase.
- The longer the surfactant chain, the more energetically favorable adsorption at interfaces and the greater the tendency for the molecule to leave the aqueous phase.
- Traube's rule describes how the ratio of surfactant concentration at the surface, to the bulk concentration, increases with the number of methylene groups in the alkyl chain. This occurs due to the increase in the tendency to escape from the aqueous phase.
- Emulsions (colloidal mixtures of two immiscible liquids) are stabilized by surfactants, forming a boundary film between the phases.
- Surfactants are used in various pharmaceutical preparations (e.g., emulsifying agents, detergents, solubilizing agents, wetting agents, foaming & antifoaming agents, flocculating agents).
- Several methods exist for measuring surface tension (e.g., Wilhelmy plate method, du Nouy tensiometer).
Measurement Methods
- Wilhelmy Plate: A thin plate dipped into the liquid; the force needed to remove it is measured to calculate surface tension. Zero contact angle is important for accurate readings. Can be used in static mode to track changes in surface tension over time.
- du Nouy Tensiometer: A platinum ring is dipped into the liquid and the force to detach it from the surface is measured to establish surface tension. Requires zero contact angle and a correction factor for accurate readings.
Calculation Examples
- Calculation of surface tension from a Wilhelmy plate force measurement involves dividing the measured detachment force by the perimeter of the plate. Ensuring all measurements are in consistent unit systems (e.g., meters).
Surfactant Action/Examples
- Liquid paraffin and water emulsions: Surfactants reduce interfacial tension between immiscible liquids, allowing them to be mixed and creating a stable emulsion.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Explore the intricate properties of surface tension and surfactants in liquids. This quiz delves into the physics of liquid interfaces, the concept of interfacial tension, and the energetic dynamics involved in surface area changes. Perfect for MPharm students looking to deepen their understanding of these essential topics.
