Question

Question 1:

a) What are the advantages and disadvantages of each technique? ( Be specific about each type of chromatography as well as extraction)

b) When would the application of each technique be appropriate?

c) What are the factors that affect the separation of substances in each technique?

1) Is it better to do a series of small volume extractions or one large one? Explain why.

2) TLC: What factors affect the Rf values?

3) Column Chromatography: What factors affect the separation on the column?

Answer 1

a) What are the advantages and disadvantages of each technique? ( Be specific about each type of chromatography as well as extraction)

advantages

chromatography --> ideal for identificaiton of compounds / Separation of compounds

extraction --> ideal for organic/aqueous solvents; ideal if good Kd constant of extraction for products

disadvantages

chromatography --> requires two phases, and polarity/affinity of solute to solvent/stationary phases. May require more complex techniques

extraction --> will only work for good distribution coefficients,

b) When would the application of each technique be appropriate?

Depends mainly on type of species; for a reaction, for instance, we will want to see te progress/extent of reaction, so chromatography will be good idea.

Also, idnetificaiton of unkown species .

For extraction --> when the solute is well known and we want to make liquid/liquid extraction in order to purify chemicals/solvents

c) What are the factors that affect the separation of substances in each technique?

  1) Is it better to do a series of small volume extractions or one large one? Explain why.

The formula:

q = [V1/(V1+K*V2) ] ^n

where

q = fraction of solute presnet after extraction

V1 = phase 1 volume; V2 = phase 2 volume; K patition coefficient, n = number of paritions

then

q = [V1/(V1+K*V2) ] ^n

as N increases, Q incrases, therefore, % purifcation increases

choose many small extractions

2) TLC: What factors affect the Rf values?

Rf -- > solvent front size / polarity of solvent / polarity of stationary phase, retention time

3) Column Chromatography: What factors affect the separation on the column?

solvent front size / pressurization / polarity of solvent / polarity of stationary phase, retention time