Essential Questions: Distribution Flashcards
Explain the difference between adsorption and absorption.
Adsorption occurs at the surface while absorption takes place inside the molecule (in a matrix).
For adsorption, there might be more specific binding sites that have higher affinity for binding.
Implications of point 1 for (a) isotherms, (b) competition effects, and (c) release kinetics?
(a) Adsorption: start in origo, steep curve in the beginning; Absorption: proportionality.
(b) Adsorption: Yes, limited amount of “spots” on the surface area. The molecules on site can compete; Absorption: No, no expected competition effects. Linear relationship.
(c) No clear cut. There are cases where it can be faster/slower.
How can sorption lead to mobilization of contaminants?
The contaminants may be carried by vectors and thereby transported to other areas, e.g. they can sorb to colloids and be transported (co-transport).
They can also be transported in fx a river where sediment is being moved by the water.
Desorbing a chemical by adding a competitive chemical - the chemical sorbs to the materials and “kicks out” the other chemical.
What is aging?
At the time of pollution, the solute and sorbent go together. Aging increases with time, i.e. sorption (Kd) increases with time.
What are the physical reasons for aging?
It takes time for the compounds to reach affinity sites and for them to go into the deeper parts of the matrix (diffusion). Physical entrapment of molecules e.g. like weathering, undergoing different season.
Does Henry’s Law apply to low environmental concentration?
Yes, only at low concentrations. For high concentrations, Rault’s law is used as the chemicals start to behave like substances.
(note: Concentrations found in the environment are usually low.)
Does diffusion at interphases (e.g. sediment-water) always go from high to low concentration?
No, because it goes from high to low chemical acitivity, e.g. the water solubility could be larger than the vapor pressure.
How can distribution be used for solving environmental pollution problems? Can you come up with 3 examples?
1) Addition of a sorbent to remove a chemical from the water phase in e.g. a lake. A sorbent could be an activated carbon filter.
2) Air cleaner/purifier that uses activated carbon.
3) Stripping in a WWTP. Here, air is sent through the wastewater to remove any pollutants.
How can you calculate Koctanol,air from Kow and Kair,water?
Koa = Kow/Kaw
