Summary
Summary Revision questions Science of medicine year 1
- Module
- Pharmacy (MASTERS)
- Institution
- The University Of Birmingham (UBir)
Revision questions and answers.
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By: Ritsy1 • 1 year ago
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What is Laplace pressure?The pressure difference across a curved surface or interface. The pressure inside is greater than the
pressure outside, the pressure inside must be strong enough to overcome the atmospheric pressure
and the surface tension.
Work is done against surface tension (to prevent the pull inwards) so the bigger the surface area the
more work needs to be done
W =∆ G=γ ∆ A
W = work done = increment free energy (ΔG) (both in J)
γ = surface tension (N/m)
ΔA = change in surface/interface area (m2)
Explain the phenomenon behind spreading and wetting?
Spreading is phenomenon liquid-liquid interphase
Wetting solid-liquid
When ad
When adhesion is > cohesion there is enough affinity for 2 phases to interact, this creates a film 1
interface like milk in tea, contact angle is smaller
When adhesion is < cohesion 2 phases wont interact so more work needs to be done to overcome
surface tension very unstable creates 1 interface but 2 surfaces
So at hydrophobic surfaces adhesion is < cohesion low affinity between 2 interphases and less
interaction contact angle is high
Hydrophilic opposite
The fabric of waterproof clothing is coated with a product that is hydrophobic. This means that the
contact angle is high, there is low affinity between the raindrops and the clothing, so the raindrops
sit on top of the surface.
Why do surfactants act on 2 phases?
Because they are ampiphillic
What are the different affinities for solvents?
Solvent hating-lyophobic
Solvent loving-lyophillic
Both-ampiphillic
What are lyophobic colloids?
Poorly solvated
They have low affinity for cont/disp phase very unstable dispersions require energy to form
∆ G=γ ∙ ∆ A−T ∆ S
, ΔG – change in the free energy of the system
γ . ΔA – energy available for work
-TΔS – entropy contribution
There is a rigid order of solvent molecules cage structure around lyophobic colloids
dispersions, so entropy is negative not spontaneous
Give and explain association colloid?
Phospholipid has1 polar tail and 2 apolar tail, from lamellar phases polar head in
water tails sticking out from liposome which are colloidal drug carriers
Surfactants have a polar had and only 1 apolar tail, they from micelles which behave
a lyophilic colloids
When surfactant concentration increases at surface they become completely
saturated no more molecules can position themselves polar head face water and
tails interacts with air until CMC critical micellar concentration at which they start to
form micelles.
What is the difference between cloud point and kraft point?
Krfat point is the temperature above where surfactant solubility increases, micelles
formation depends on surfactant concemtartioon and temperature.
Temperature below kraft point cause surfactant molecules to ppt instaed of forming
micelles.
Cloud point is temperature above where surfactant solubility decreases as the polar
head becomes dehydrated froms cloudy solution, reversible if temp lowered below
cloud point.
Give examples of a good solvent and bad solvent?
In a good solvent the colloid will act as a lyophilic colloid as it will want to maximise
its interaction with the dispersing phase so will adopt a extended shape results in low
surface tension almost nil so dispersion spontaneous
Bad solvent colloid will act lyophobic so will reduce interaction from spherical shape
with dispersing phase and will aggregate at bottom result in more surface tension
dispersion require energy.
Explain how optical properties of colloidal dispersion can be used to distinguish
them?
Light scattering-if you shine light through solution a clear solution light will pass
through but in colloid solution light will scatter. This can be seen under
ultramicroscopy as light will appears spots against dark background
Explain the electrical properties of colloidal dispersions?
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