Adsorption and Absorption Flashcards

1
Q

What is absorption?

A

a fluid permeates or is dissolved by a liquid or solid

process where a substrate originally present in one phase or compartment is diffused into another phase/compartment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is adsorption?

A

adhesion of molecules of gas, liquid or dissolved solid to a solid surface

describes the tendency of materials to locate at a solid surface in a concentration different than that found in the surrounding medium (bulk)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the features of absorption?

A

irreversible - drug cannot be retrieved when absorbed

bulk phenomenon - whole substance is affected and taken in

endothermic - energy of absorbent increases/ energy taken in

uniform rate

temperature has no effect

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the features of adsorption?

A

reversible

  • can be reversed by reducing pressure, reducing temperature, changing pH
  • interaction is only between particles at the interface
  • interaction is based on Van der Waals forces which are weak

surface phenomenon = takes place at surface/ only those at the surface are affected
exothermic - energy of surface decreases
non-uniform rate - increases steadily until it reaches equilibrium
temperature dependent - favours low temperatures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are examples of products functioning by adsorption?

A
enterosgel intestinal adsorbent 225g
silica gel
activated characoal
activated aluminates
zeolites
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is an adsorbent and adsorbate?

A

adsorbent - surface where adhesion occurs

adsorbate - molecules of solute

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How does activated charcoal work?

A

used to remove harmful substances from the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the requirements for an effective adsorbent?

A

1 - small size = usually spherical pellets or rods with diameters between 0.5-10mm
2 - high surface area = small pore diameters and high thermal stability increase area exposed for adsorption
3 - active sites or hydrophobic sites = must have distinct reactive functional groups or hydrophobic groups

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the three different classes of adsorbents?

A
oxygen containing compounds
- typically hydrophilic and polar
carbon based compounds 
- typically hydrophobic and non-polar
polymer based compounds 
- polar or non-polar functional groups in a porous polymer matrix
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the advantages of adsorption?

A

can be used in emergency treatment of drug overdose

  • administration of a water powder slurry (suspension) of activated carbon into the GIT by either oral or nasogastric tube
  • many drugs have a high binding affinity for it
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the disadvantages of adsorption?

A

loss of drug potency

  • drug can accumulate at the surface of the container through unspecified hydrophobic forces = instead of interacting in solution
  • loss of proteins from the bulk solution
  • unfolding of proteins can occur = non-functional
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How does adsorption occur?

A

occurs via weak physical forces rather than chemical alteration

  • hydrogen bonding
  • hydrophobic forces
  • Van der Waals forces
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is Langmuir-Hinshelwood mechanism?

A

reaction occurs with 2 species

  • between 2 adsorbed reactants
  • both are adsorbed onto the surface of the catalyst and a product is formed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How do you work out the rate of formation in Langmuir-Hinshelwood mechanism?

A

to find out rate, the extent of surface coverage is needed
- depends on surface covered

expect rate law to be in second order

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the Eley-Rideal mechanism?

A

reaction occurs between 2 species

  • between an adsorbed reactant and a non-adsorbed reactant
  • gas molecules collides with another molecule already adsorbed onto the catalyst

the rate determining step is the collision between the them

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How do you work out the rate of formation in Eley-Rideal mechanism?

A

to find out the rate, partial pressure of the rolling gas and surface coverage by the adsorbed species is needed

  • allows prediction of how much of a drug can be adsorbed onto a specific surface
17
Q

What are the assumptions made by the Langmuir-Hinshelwood mechanism?

A

solid surface contains a constant number of identical adsorption sites

each adsorption sites takes one molecule forming a monolayer

no adsorbate-adsorbate interactions

whole process is at constant temperature