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Questions and Answers
What primarily causes surface tension in liquids?
What primarily causes surface tension in liquids?
Which of the following best describes interfacial tension?
Which of the following best describes interfacial tension?
Which of the following is NOT a type of interface?
Which of the following is NOT a type of interface?
In emulsion formation, what role do surfactants typically play?
In emulsion formation, what role do surfactants typically play?
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What causes the high interfacial tension between oil and water?
What causes the high interfacial tension between oil and water?
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Which statement best describes interfacial tension?
Which statement best describes interfacial tension?
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What is the effect of cohesive forces in a liquid on its surface behavior?
What is the effect of cohesive forces in a liquid on its surface behavior?
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What is the role of surfactants in emulsion formation?
What is the role of surfactants in emulsion formation?
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Which factor can influence the viscosity of a liquid?
Which factor can influence the viscosity of a liquid?
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What occurs at the boundary of a liquid and a solid surface?
What occurs at the boundary of a liquid and a solid surface?
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Which of the following best explains why water and benzene do not naturally mix?
Which of the following best explains why water and benzene do not naturally mix?
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What is a characteristic of high interfacial tension in suspensions?
What is a characteristic of high interfacial tension in suspensions?
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Which condition is necessary for the formation of an emulsion?
Which condition is necessary for the formation of an emulsion?
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In terms of surface tension, what effect do surfactants have?
In terms of surface tension, what effect do surfactants have?
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Why is it noted that there is no interfacial tension between two miscible liquids?
Why is it noted that there is no interfacial tension between two miscible liquids?
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How does low interfacial tension affect a liquid's wettability?
How does low interfacial tension affect a liquid's wettability?
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What do cohesive forces primarily act upon?
What do cohesive forces primarily act upon?
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Which statement about the molecules at the surface of a liquid is incorrect?
Which statement about the molecules at the surface of a liquid is incorrect?
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What is the primary effect of adding surfactants to a liquid consisting of two immiscible phases, such as oil and water?
What is the primary effect of adding surfactants to a liquid consisting of two immiscible phases, such as oil and water?
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Which of the following is a practical application of surface tension?
Which of the following is a practical application of surface tension?
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What is likely to happen when two immiscible liquids are mixed without a surfactant?
What is likely to happen when two immiscible liquids are mixed without a surfactant?
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How does viscosity relate to the cohesive forces within a liquid?
How does viscosity relate to the cohesive forces within a liquid?
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Which of the following statements about adhesive forces is true?
Which of the following statements about adhesive forces is true?
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Which factor plays a significant role in determining interfacial tension between two immiscible phases?
Which factor plays a significant role in determining interfacial tension between two immiscible phases?
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Study Notes
Surface Tension and Surfactants
- Surface tension is the force that pulls inward on the surface of a liquid, caused by cohesive forces between liquid molecules.
- Interfacial tension occurs at the boundary between two immiscible liquids.
- Water and oil are immiscible, meaning they do not mix. This is due to differences in polarity, which affects how molecules attract each other.
- Surfactants are molecules with a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail. They reduce surface tension by disrupting the cohesive forces between water molecules.
- Pharmaceutics is the science of dosage form design.
- Dosage forms are carriers for drug molecules delivered to different body sites.
- Dosage forms combine the drug with excipients (non-drug components).
Important Definitions
- An interface is the boundary between two phases.
- Common phase types include gas-liquid, gas-solid, liquid-liquid, liquid-solid, and solid-solid.
- Emulsions are mixtures of two immiscible liquids.
- Suspensions are mixtures where solid particles are dispersed in a liquid.
Surface Tension
- Surface tension is the inward pull on the surface of a liquid caused by the cohesive forces between water molecules.
- Unbalanced forces at the surface lead to liquid tension.
- Cohesive forces are stronger than adhesive forces between water and air moleculs.
Interfacial Tension
- Interfacial tension occurs at the boundary between two immiscible liquids.
- Miscible liquids do not have interfacial tension.
Surface tension in Pharmaceutics
- Emulsions are mixtures of immiscible liquids like oil and water.
- Polarity differences cause immiscibility.
- Surfactants reduce interfacial tension, enabling mixing.
- Suspensions have high interfacial tension between solids and liquids, so they don't mix.
How surfactants reduce surface tension
- Surfactants interrupt cohesive forces between water molecules by inserting themselves between water molecules.
- Hydrophobic tails are repelled by water; hydrophilic heads attract water molecules.
What is an emulsion?
- An emulsion is a mixture of two immiscible liquids.
- A heterogeneous mixture.
Practice Questions
- Water and benzene: Water and benzene are immiscible. They do not naturally mix.
- Water and acetic acid: Water and acetic acid are miscible.
- Water and CCl4: Water and CCl4 are immiscible. They can be mixed by adding surfactants to form an emulsion.
- Emulsion formation: Emulsions form when surfactants reduce interfacial tension between immiscible liquids.
- Different oils have different interfacial tensions with water.
- Miscibility with water: Only one oil (sunflower oil) is miscible with water. Miscibility depends on molecules' polarity.
- Surface Tension: The resistance of a liquid to an increase in its surface area.
- When no external forces: Surface tension determines a liquid drop's shape in the absence of external forces.
- Temperature and surface tension: As temperature increases, surface tension decreases.
- Boundary between phases: The boundary between two or more phases is called an interface.
- Interfacial tension of completely miscible liquids: If liquids are completely miscible, the interfacial tension is zero.
- Forces on a falling liquid drop: Gravity exceeds the adhesive forces for a liquid drop to fall.
- Interfacial tension existence: Interfacial tension exists between immiscible liquids.
- Molecules in a liquid bulk: Molecules in a liquid bulk have equal attraction from surrounding molecules.
Additional Practice Questions
-
What is the main result of adding surfactants into a liquid composed of two immiscible phases?
- Surfactants decrease the interfacial tension between liquids, allowing the mixture to be formed.
-
Which of the following is an application of surface tension?
- Use of soaps and detergents, and incorporation into substances like toothpaste.
Reference Book
- Martin's Physical Pharmacy and Pharmaceutical Sciences by Patrick J. Sinko (2017).
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Description
Explore the concepts of surface tension and surfactants in pharmaceutics. Learn how surfactants modify surface and interfacial tension, influencing dosage form design. This quiz delves into the science of how these elements interact in various phases.
