Ochem Chapter 12 Purification And Separation

Front 1

extraction process

Back 1

transfer of a dissolved compound(desired product) from a starting solvent into a solvent in which the product is more soluble

Front 2

extraction is based on the principle "like dissolves like/unlike"
examples

Back 2

like dissolves like
polar --> polar
non-polar --> non-polar

Front 3

a polar substance will dissolve best in a polar/non-polar solvent

Back 3

polar

Front 4

with extractions, it is important to make sure that the two solvents are miscible/immiscible

Back 4

immiscible
-the two layers are temporarily mixed so that solute can pass from one to the other

Front 5

after mixing the two immiscible layers, how to get desired product?

Back 5

two layers will eventually separate again
-use of a separatory funnel and gravity will allow heavier layer to sink to the bottom and can be removed

Front 6

in general the organic/aqueous layer will be on top and the organic/aqueous layer will be on the bottom

what are the dependent upon?

Back 6

organic = top
aqueous = bottom

-densities

Front 7

one is then capable of removing the aqueous layer from the organic layer and remove the product in the process

Back 7

know

Front 8

process must be repeated until all product removed from the aqueous layer

Back 8

know

Front 9

which will yield a higher yield?
3 x 10mL or 1 x 30mL solvent?

Back 9

3 x 10mL will be > than 1 x 30mL

this is because each individual wash is capable of retrieving slightly more than the previous...pg 212

Front 10

what are the 3 intermolecular forces that affect solubility?

Back 10

1. h-bonding: alcohols, water, amines, carboxylic acids
--these will move most easily into the aqueous layer(h2o)
2. dipole-dipole interaction: these compounds are less likely to move into the aqueous layer
3. london forces: compounds are least likely to move into aqueous layer

Front 11

what does a 'wash' entail?

Back 11

perform reverse process of extraction to remove unwanted impurities
-washing the product of unwanted impurities

Front 12

problem: HA + Base --> A- + Base:H+
scenario...which is more soluble in aqueous layer... HA or A-?

Back 12

when acid dissociates the anion formed will be more soluble in the aqueous layer because it is charged
-addition of a base will help extract an acid H+

Front 13

filtration

Back 13

isolates a solid from a liquid

Front 14

filtration process

Back 14

pour liquid into object covered in filter paper and separate components

-solid forms on the filter paper and the remaining liquid becomes the filtrate

Front 15

2 methods of filtration

Back 15

gravity
vacuum

Front 16

gravity filtration

Back 16

solvents weight pushes itself through the filter paper
-slower rate of filtration
-usually want substance to be dissolved in solution hence the use of hot/warm solvent

Front 17

vacuum filtration

Back 17

solvent is forced through the filter using a vacuum..

-quick and does not require hot solvent
-used when need to separate large quantities of substance

Front 18

difference in desired products between two filtration processes?

Back 18

gravity = liquid left over(want substance in the solution)

vacuum = solid left over(want substance separated from the solution)

Front 19

pure substances will have higher solubility at ___ temperatures and lower solubility at ___ temperatures

Back 19

higher
lower

Front 20

impurities within a substance will not drastically affect the solubility at varied temperatures...aka it will stay nearly constant

Back 20

know

Front 21

recrystallization

Back 21

performed after filtration occurs
-purifies product further by removing impurities

Front 22

trick with recrystallization and solvent preference...want a solvent that makes the solid soluble at high/low temperatures only and soluble/insoluble at lower temperatures

Back 22

high
insoluble

Front 23

when the solution cools from hot to cold, only the solid product will recrystallize

Back 23

know

Front 24

trick with recrystallization and solvent preference... need to know polarity of the solvent
-needs low enough freezing point but can not allow to be frozen..

Back 24

know

Front 25

a mixed solvent system may be used...process?

Back 25

1. dissolve solid in solvent that it is highly soluble in at higher temperature
2. begin to add a solvent that is less soluble with solid...drop-wise fashion until the solid precipitates
3. heat mixture to allow complete dissolvation and then allow to cool and remove through vacuum filtration

Front 26

sublimation

Back 26

heated solid --> gas
-can act as a method of purification since impurities will not sublime easily

Front 27

sublimation process

Back 27

produce vapors that condense on a chilled glass called a cold finger
-most likely performed under a vacuum since at lower pressures the substance is more likely to undergo sublimation

Front 28

reduction in pressure for a sublimation will also increase/decrease the temperature required for the substance to sublimate at

Back 28

decrease
-reduces chance of decomposition

Front 29

centrifugation

Back 29

particles settle and separate at different rates based on mass, density and shape

Front 30

examples that centrifugation can be used in...

Back 30

separate components of blood
separate organelles
separate DNA molecules

Front 31

simple distillation

Back 31

basic kind of distillation
used to separate liquids that boil below 150C and have at least a 25C difference between the two BP

Front 32

vacuum distillation

Back 32

used with substances that boil over 150C

Front 33

the use of a vacuum in this kind of distillation will increase/decrease the vapor pressure and in return increase/decrease the temperature needed to boil at

Back 33

decrease
decrease
-no worries of degrading the compound

Front 34

fractional distillation

Back 34

used when you want to separate two liquids with similar BP (<25C difference)

Front 35

fractional column involves a column filled with steel wool, etc to increase/decrease the surface area

Back 35

increase

Front 36

chromatography general principle; the more similar the compound is to its surroundings, the slower it will move through them

Back 36

know

Front 37

chromatography process

Back 37

1. requires solid medium = stationary phase
2. run mobile phase(liquid) through stationary phase
3. process will elute/separate it from original location on stationary phase and carry it with the mobile phase

Front 38

distance moved on the stationary phase depends on polarity and speed

Back 38

know

Front 39

TLC: thin layer chromatography

Back 39

use of silica gel (highly polar substance) as stationary phase
---any polar compound will adhere to the stationary phase and not move much.....

Front 40

TLC = capillary action up the stationary phase paper

Back 40

know

Front 41

mobile phase of TLC is usually organic/inorganic in nature while the stationary phase is polar/nonpolar and hydrophilic

Back 41

organic
polar

Front 42

non polar compounds will be carried by the polar/non polar stationary/mobile phase

Back 42

nonpolar mobile phase

Front 43

reverse phase chromatography

Back 43

stationary phase is non-polar
mobile phase is polar

Front 44

Rf values are calulated by...

Back 44

(distance compound traveled) / (distance solvent traveled)
-used to identify the compound if unknown

Front 45

column chromatography

Back 45

has column filled with silica gel
-allows for greater separation
-can use gravity or nitrogen

Front 46

flash column chromatography

Back 46

faster
-use of N2 to push liquids through the column
-collect fractions compared to various times separated

Front 47

column chromatography can be used to separate proteins/nucleic acids

Back 47

know

Front 48

ion exchange chromatography

Back 48

beads in column are coated with charged substances and will attract/bind compounds that have an opposite charge
-this will affect the time of separation
-salt gradient used to remove the charged molecules that are stuck in the column

Front 49

size-exclusion chromatography

Back 49

beads used have tiny pores of varying sizes; allow small compounds to enter the beads, slowing them down
-large compounds can not fit into the pores an will move around them...they will elute faster
-SMALL COMPOUNDS RETAINED LONGER THAN LARGE ONES

Front 50

affinity chromatography

Back 50

can be customizable to selectively bind/have affinity for a molecule...it will remain in the column longer if bound...can be removed from column using a free receptor that releases the bind by competing for affinity
-DISADVANTAGE; inhibitor/receptor now bound to separated component; can be difficult to remove (pg 222)

Front 51

gas chromatography

Back 51

the eluant is a gas(He or N2)
the liquid sample is injected, vaporized and the compounds travel through at different rates

Front 52

GC requirement: the compounds injected must be volatile/involatile

Back 52

volatile
= low MP, sublimable solids/liquids

Front 53

HPLC: high-performance liquid chromatography

Back 53

-the eluant is a liquid
-travels through column of defined composition
-sample injected
-lower pressure used
-similar to GC process

Front 54

electrophoresis

Back 54

used to separate a mixture of compounds that carry a charge
-used with protein and DNA
-use of electric field
-particles move according to charge and size

Front 55

negatively charged particles(DNA) will move towards the +/- cathode/anode

Back 55

+ charged ANODE
NOTE THIS CHANGE!!!
pg 224 for clarification

Front 56

positively charge compounds will migrate toward the +/- anode/cathode

Back 56

- charged CATHODE

Front 57

migration velocity =
v = (Ez / f)

Back 57

E = electric field strength
f = frictional coefficient
z = net charge on the molecule

(f is dependent upon the mass and the shape of the migrating molecules)

Front 58

the more charged the molecule or the stronger the electric field is, the faster/slower it will migrate through the medium

Back 58

faster

Front 59

agarose gel electrophoresis

Back 59

separate nucleic acids
medium used is agarose

Front 60

every nucleic acid is negatively charged; they can therefore be separated on the basis of size and shape alone

Back 60

know

Front 61

to make gel run faster; increase ___ or decrease the amount of ___

Back 61

voltage = E
agarose = f

Front 62

SDS-PAGE = sodium dodecul sulfate-polyacrylamide gel electrophoresis

Back 62

separates proteins on the basis of mass alone; procedure denatures proteins

Front 63

SDS disrupts all non/covalent bonds

Back 63

non-covalent bonds

Front 64

SDS binds to proteins and creates large chains with net negative charges, thereby neutralizing the protein's original charge

Back 64

know

Front 65

the only variable affecting velocity is ___

Back 65

f = frictional coefficient

Front 66

the frictional coefficient depends on ____

Back 66

mass

Front 67

isoelectric focusing

Back 67

exploits the acidic/basic properties of amino acids

Front 68

each protein may be characterized by its isoelectric point (pI), which is the pH at which its net charge is ____

Back 68

zero

Front 69

scenario: take a mix of proteins and place them in an electric field that exists across a gel with a pH gradient(acidic on one side and basic on the other) the proteins will move until they reach the point that has a pH = to....

Back 69

their pI

Front 70

when pH = pI...

Back 70

the proteins net charge is zero and it will stop moving

Front 71

if protein of pI = 9 placed in pH other than pH 9, it will carry a charge...

Back 71

know

Front 72

if placed in a pH lower than pI, it will have more protons/electrons, creating a positive/negative charge on the protein

Back 72

protons
positive

Front 73

if the protein carries a positive charge, it will move towards the (-) cathode

Back 73

know

Front 74

cathode = acidic/basic
anode = acidic/basic

Back 74

basic
acidic

Front 75

if pH higher than pI (placed in basic soln) the protein will carry a negative charge and move toward the (+) anode

Back 75

know