Hosam Mohamed
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bulk; equal forces
Molecules in the____ phases experience _______ from all directions
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interface; same; neighboring
Molecules at _________ experience high attractive forces from molecules of the ______ kind and lower attractive forces from molecules of the _______ phase.
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Surfactants
-substances that possess both hydrophilic and lipophilic parts
-also known as amphiphiles
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move to surface or interface of liquid; lower surface tension
How do surfactants work?
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Na & K salts of straight-chain fatty acids/ soaps, sulfonates, sulfates
What are some anionic surfactants?
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quaternary ammonium salts, antibacterial agents, benzalkonium chloride
What are some cationic surfactants?
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soaps
Cationic surfactants are incompatible with ________.
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Non-ionic surfactants
-not electrolytes and do not have a charge
-not affected by pH and presence of salts.
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Hydrophile - Lipophile Balance (HLB)
-balance between hydrophilic and lipophilic groups determines the utility of a surfactant
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more lipophilic
Smaller HLB number = ?
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lipophilic; oil
Surfactants with HLB values <9 are ______ and forms water in ___ emulsions.
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hydrophilic
Higher HLB number =
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Surface tension
the force per unit length that must be applied to the surface so as to counterbalance the net inward pull.
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dynes/cm
What is the unit for surface tension?
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when contact angle is 0 or very small
When do we use Capillary rise method?
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Capillary rise
Which surface tension method cannot be used to measure interfacial tension?
- Du Nouy Ring Method
- Capillary Rise
- Wilhemy Plate Method
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cannot; not wetted
When liquids __________ spread over surface a solid, the solid is ______.
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the liquid must displace air surrounding solid particles and spread over the surface
Why does talc or charcoal powder float when sprinkled on water, despite it having a lower density than water?
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Contact angle
-parameter used to measure the tendency of a liquid to wet a solid surface.
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poor wetting
Large contact angle =
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complete
Contact angle of 0 signifies _________ wetting.
partial
poor
complete
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Wetting agents
- surfactants that assist in wetting by lowering contact angle
-reduce contact angle between solid and liquid
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reduce contact angle by reducing both liquid surface tension and interfacial tension
How do wetting agents work?
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Emulsion
two-phase system in which one liquid is dispersed throughout another liquid in the form of small droplets
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Coalescence
-merging of small droplets into larger droplets with eventual complete separation of phases.
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true
Coalescence involves larger droplets that can not be re-emulsified by simple shaking. T or F?
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Suspensions
-liquid formulations that consist of solid particles dispersed throughout a liquid phase in which the particles are not soluble.
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Suspensions
hard settlement of particles at the bottom of the bottle which can not be resuspended
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pH & pka
Ionization of functional groups is a function of _____ & _______.
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Stern layer
-layer that rigidly attached to the surface of the solid particle.
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Gouy-Chapman layer
-layer that is not rigidly attached to surface of solid particles.
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stern layer; gouy-chapman layer; zero
Electrical potential drops rapidly across ________ and less rapid across _____ and ultimately reaches _________.
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double layer
What will cause 2 particles to repel each other when they are coming into close proximity of one another?
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Zeta potential
- the magnitude of repulsive forces between particles
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adding electrolytes
How can we measure and change zeta potential?
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Defloculated system
-smaller, lighter, settles slowly, stronger repulsion, cakes form.
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Floculated system
-large, heavier, settles faster, weak attraction between particles, easy redispersion.
