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Questions and Answers
What is the net effect of the forces experienced by molecules at the surface of the liquid?
What is interfacial tension?
Why are interfacial tensions generally less than surface tensions?
Why do micelles form when more surface active agent is added to water?
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What happens to the solubility of a drug when the concentration of the surface active agent increases beyond the CMC concentration?
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What does a higher HLB number indicate about a surfactant?
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How do particles dispersed in water acquire a negative charge?
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What is the main reason for particles dispersed in water to acquire a negative charge?
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What is the source of charges on particles dispersed in liquid media?
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How do cationic quaternary compounds affect gram-negative and gram-positive organisms?
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What is the net charge of the protein at its isoelectric point?
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What happens to the protein at low pH?
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What is the term for the specific pH at which a protein exists as a Zwitterion?
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What happens to the protein at high pH?
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What causes anions to be attracted to a positively charged surface in a polar solution?
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What leads to the formation of micelles in the bulk when more surface active agent is added to water?
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Why do micelles form when more surface active agent is added to water?
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What does the hydrophile–lipophile balance (HLB) number measure in a surfactant?
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What is the impact of a higher HLB number on a surfactant's function?
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What happens to the solubility of a drug when the concentration of the surface active agent increases beyond the CMC concentration?
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How do particles dispersed in water mainly acquire a negative charge?
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What leads to the selective adsorption of the hydroxyl ion onto particles dispersed in water?
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What is the primary source of charges on particles dispersed in liquid media?
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What is responsible for the charges on particles dispersed in liquid media being a function of pH and pKa?
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How do cationic quaternary compounds affect gram-negative and gram-positive organisms?
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Study Notes
Forces at Liquid Surface
- Molecules at the surface experience net inward forces, leading to minimized surface area.
- Surface tension results from cohesive forces between liquid molecules.
Interfacial Tension
- Interfacial tension is the force at the interface between two different phases, such as liquid-liquid or liquid-gas.
- It is generally lower than surface tension due to differing intermolecular interactions.
Formation of Micelles
- Micelles form when excess surface-active agents aggregate in solution, minimizing energy by sequestering hydrophobic tails.
- Above the critical micelle concentration (CMC), solubility of certain drugs decreases due to saturation of surfactant.
HLB Number Significance
- A higher hydrophile-lipophile balance (HLB) number indicates a more hydrophilic surfactant, which is generally used for oil-in-water emulsions.
- An HLB number helps tailor surfactants to specific applications based on desired interactions.
Charge Acquisition in Dispersed Particles
- Particles dispersed in water mainly acquire a negative charge through selective adsorption of ions, particularly hydroxyl ions (OH⁻).
- The main source of charges is surface functional groups interacting with ions in the solvent.
Protein Behavior with pH
- At the isoelectric point, the net charge of protein is zero, and it precipitates out of solution.
- Low pH makes proteins positively charged, leading to solubility.
- At high pH, proteins tend to acquire negative charges and can become less soluble.
Micelles and Surfactants
- Micelle formation occurs in bulk when hydrophobic portions of surfactants aggregate, reducing surface energy.
- Selective adsorption of hydroxyl ions enhances negative charges on particle surfaces.
Impact of Cationic Compounds
- Cationic quaternary compounds can disrupt cell membranes of gram-negative and gram-positive organisms, affecting their viability.
pH and ion Influence on Particles
- The charges on particles in liquid media are dependent on pH due to equilibrium of acid-base dissociation affecting surface charge density.
- The dynamic nature of charges is influenced by the pKa of functional groups present on particles.
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Description
Explore the characteristics of interfacial phenomena in liquids, including the differences in cohesive and adhesive forces experienced by molecules at the bulk and surface of the liquid. This quiz delves into Chapter 15 of interfacial phenomena.
