Podcast
Questions and Answers
What effect do soaps and detergents have on surface tension?
What effect do soaps and detergents have on surface tension?
At what temperature is the surface tension of water measured as 72 mN m-1?
At what temperature is the surface tension of water measured as 72 mN m-1?
Which substance listed has the lowest surface tension?
Which substance listed has the lowest surface tension?
What is the surface tension of mercury, as given in the values?
What is the surface tension of mercury, as given in the values?
Signup and view all the answers
What happens to surface tension in the presence of impurities?
What happens to surface tension in the presence of impurities?
Signup and view all the answers
What phenomenon causes the surface molecules of water to exhibit a 'skin' that resists puncture?
What phenomenon causes the surface molecules of water to exhibit a 'skin' that resists puncture?
Signup and view all the answers
What is the typical lifetime of a molecule at the surface of water?
What is the typical lifetime of a molecule at the surface of water?
Signup and view all the answers
What is the definition of surface tension?
What is the definition of surface tension?
Signup and view all the answers
What energy is required to increase the surface area of a liquid isothermally and reversibly by 1 m²?
What energy is required to increase the surface area of a liquid isothermally and reversibly by 1 m²?
Signup and view all the answers
How are surface tension and surface free energy related?
How are surface tension and surface free energy related?
Signup and view all the answers
What effect does increasing the temperature have on the surface tension of water?
What effect does increasing the temperature have on the surface tension of water?
Signup and view all the answers
Why is hot water considered a better cleaning agent than cold water?
Why is hot water considered a better cleaning agent than cold water?
Signup and view all the answers
What is the surface tension of water at 25°C?
What is the surface tension of water at 25°C?
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
Which of the following describes the phenomenon where water droplets form a spherical shape?
Which of the following describes the phenomenon where water droplets form a spherical shape?
Signup and view all the answers
What occurs at the liquid-liquid interface compared to the gas-liquid interface?
What occurs at the liquid-liquid interface compared to the gas-liquid interface?
Signup and view all the answers
Which statement about surface free energy is correct?
Which statement about surface free energy is correct?
Signup and view all the answers
What is the relation between particle size and surface free energy in solids?
What is the relation between particle size and surface free energy in solids?
Signup and view all the answers
What is the main characteristic of a surface that is different from the bulk in terms of energy?
What is the main characteristic of a surface that is different from the bulk in terms of energy?
Signup and view all the answers
Why are fine particles challenging to handle?
Why are fine particles challenging to handle?
Signup and view all the answers
Which term refers to the energy difference between the surface and bulk of a substance?
Which term refers to the energy difference between the surface and bulk of a substance?
Signup and view all the answers
What does the angle θ indicate when measuring contact angle for surfactants?
What does the angle θ indicate when measuring contact angle for surfactants?
Signup and view all the answers
In the Wilhelmy Plate method, what is the required condition for accurate measurement of surface tension?
In the Wilhelmy Plate method, what is the required condition for accurate measurement of surface tension?
Signup and view all the answers
Which formula correctly represents the relationship between force, perimeter, and surface tension in the Wilhelmy Plate method?
Which formula correctly represents the relationship between force, perimeter, and surface tension in the Wilhelmy Plate method?
Signup and view all the answers
If the force needed to detach a Wilhelmy Plate from a liquid is measured at 3 mN, and the perimeter of the plate is 0.049 m, what is the surface tension of the liquid?
If the force needed to detach a Wilhelmy Plate from a liquid is measured at 3 mN, and the perimeter of the plate is 0.049 m, what is the surface tension of the liquid?
Signup and view all the answers
What is the significance of a contact angle of θ < 90°?
What is the significance of a contact angle of θ < 90°?
Signup and view all the answers
Why is the Wilhelmy Plate method considered an absolute method?
Why is the Wilhelmy Plate method considered an absolute method?
Signup and view all the answers
What type of plate is typically used in the Wilhelmy Plate method?
What type of plate is typically used in the Wilhelmy Plate method?
Signup and view all the answers
When measuring surface tension, what can be inferred if the contact angle is θ = 90°?
When measuring surface tension, what can be inferred if the contact angle is θ = 90°?
Signup and view all the answers
What effect does increasing the number of –CH2 groups have on the ratio of concentration at the surface layer to that in the bulk?
What effect does increasing the number of –CH2 groups have on the ratio of concentration at the surface layer to that in the bulk?
Signup and view all the answers
What is the primary function of a du Nouy tensiometer?
What is the primary function of a du Nouy tensiometer?
Signup and view all the answers
Which type of colloidal system is an emulsion defined as?
Which type of colloidal system is an emulsion defined as?
Signup and view all the answers
What role do surfactants play in the formation of stable emulsions?
What role do surfactants play in the formation of stable emulsions?
Signup and view all the answers
Which of the following correctly describes surfactants?
Which of the following correctly describes surfactants?
Signup and view all the answers
How does shaking affect the emulsion of oil and water?
How does shaking affect the emulsion of oil and water?
Signup and view all the answers
What is the effect of increasing the carbon chain length in surfactants?
What is the effect of increasing the carbon chain length in surfactants?
Signup and view all the answers
What mathematical relationship is given for calculating detachment force using a du Nouy tensiometer?
What mathematical relationship is given for calculating detachment force using a du Nouy tensiometer?
Signup and view all the answers
What happens to the emulsion when shaking ceases?
What happens to the emulsion when shaking ceases?
Signup and view all the answers
Which surfactant is considered water-soluble for use in making o/w emulsions?
Which surfactant is considered water-soluble for use in making o/w emulsions?
Signup and view all the answers
In regard to surfactant behavior, what is Traube’s rule relevant to?
In regard to surfactant behavior, what is Traube’s rule relevant to?
Signup and view all the answers
What is required for accurate surface tension measurements using the du Nouy tensiometer?
What is required for accurate surface tension measurements using the du Nouy tensiometer?
Signup and view all the answers
What is the primary characteristic of the complex stable film formed by surfactants?
What is the primary characteristic of the complex stable film formed by surfactants?
Signup and view all the answers
Which of the following best describes the hydrophobic group in surfactants?
Which of the following best describes the hydrophobic group in surfactants?
Signup and view all the answers
Study Notes
MPharm Programme: Surface Tension & Surfactants
- This programme covers surfactants and their use in pharmaceutical preparations.
- Surface tension is the force acting parallel to the surface and at right angles to a 1m line drawn anywhere in the surface.
- Surface tension is measured in mN m⁻¹.
- Water's surface tension is 72 mN m⁻¹ at 25°C and decreases with temperature.
- Interfaces are the transition regions where two immiscible phases meet.
- Examples of interfaces include: liquid-vapour, liquid-liquid, solid-liquid, solid-vapour, and solid-solid.
- Surface tension is an inward force that causes the surface to contract.
- Surface molecules have higher energy than bulk molecules due to the unequal attractive forces.
- Reducing surface area minimizes surface free energy.
- Water droplets are spherical due to the minimization of surface area.
- Solids can't readily change shape when surface free energy is high.
- Increasing surface area (e.g., milling solids) increases surface free energy.
- To increase surface area, energy must be supplied (e.g., emulsion formation).
- Wetting is the ability of a liquid to spread on a solid surface and is influenced by contact angle. A contact angle of 0° indicates complete wetting, while an angle of 180° indicates no wetting.
- Surfactants are amphipathic molecules with both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.
- Surfactants have hydrophobic tails (like hydrocarbon chains) and hydrophilic heads which contain a charged functional group.
- This dual nature allows surfactants to adsorb at liquid-liquid or liquid-solid interfaces.
- Traube's rule states that for homologous alcohols, the ratio of surface concentration to bulk concentration increases approximately threefold for every additional -CH2 group in the chain length.
- Surfactants lower surface tension, making them useful emulsifying agents, detergents, solubilizing agents, wetting agents, foaming agents, and antifoaming agents, and flocculating agents.
- Emulsions are colloidal systems of two immiscible liquids, often water and oil.
- These systems use emulsifiers (surfactants) to stabilize the emulsion.
Measurement of Surface Tension
- Methods include the Wilhelmy plate and du Nouy ring methods.
- Wilhelmy plate: A thin plate dipped into the liquid, with force measured as it's pulled out. Surface tension is calculated with the force divided by the plate's perimeter.
- du Nouy ring: Force to detach a platinum ring from the liquid is measured. Surface tension is calculated from the detachment force and ring perimeter.
- Both require zero contact angles for accurate measurements.
- Correction factors may be needed depending on the method and specific situation (e.g., for non-vertical force).
Calculation Example
- A calculation example using the Wilhelmy plate method shows how to find surface tension values from measured force and perimeter parameters. (e.g., for a given liquid and plate dimensions)
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
This quiz focuses on the concepts of surface tension and surfactants relevant to pharmaceutical preparations. It explores the physical properties of surface tension, its measurement, and the role of surfactants in reducing surface energy in various interfaces. Test your understanding of these essential topics in the MPharm programme.
