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Chapter #12 Flashcards

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1
Q

extraction

A

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

this leaves most of the impurities behind in the first solvent.

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2
Q

when performing extractions, it is important to make sure that the two solvents are ______

A

immiscible

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3
Q

immiscible solvents

A

form two layers and do not mix

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4
Q

how do you separate the aqueous layer from the organic layer in extraction

A

use a separatory funnel

more dense layer is on the bottom.

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5
Q

what three intermolecular forces effect solubility?

A

hydrogen bonding, dipole dipole, and van der waals

in that order from most to least likely to move into the polar (aqueous layer)

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6
Q

is a single extraction with a larger volume more or less effective than many small extractions with a smaller volume?

A

more extractions with smaller volume is more effective.

compared to laundering clothes over and over (with cleaner water)

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7
Q

once the product in the aqueous layer is obtained from the separatory funnel from an extraction, what is the next step to isolate it?

A

perform a rotary evaporation (rotovap)

this evaporates the solvent

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8
Q

what is a wash extraction

A

also uses the concept of solubility properties to remove impurities from a solution. A small amount of solute that dissolves impurities is run over the compound of interest (impurities are taken out)

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9
Q

how will adding a base help to extract an acid

A

adding a base turns the acid into its conjugate base which is more soluble in the aqueous layer and thus can be removed in the aqueous phase.

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10
Q

what type of methods make use of solubility rules?

A

extraction, filtration, recrystallization

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11
Q

filtration isolates ____ from ____

A

solid from liquid

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12
Q

describe the process of filtration

A

pour a liquid solid mixture onto a paper filter that allows only the solvent to pass through.

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13
Q

compare residue and filtrate

A

residue is solid in and filtrate is liquid in a filtration

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14
Q

gravity filtration

A

solvent’s own weight pulls it through the filter

product of interest is in the filtrate

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15
Q

what type of solvent is used in gravity filtration?

A

hot solvent because this keeps the product dissolved in the liquid

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16
Q

vacuum filtration

A

the solvent is forced through the filter by a vacuum connected to the flask
product of interest is the solid (residue or precipitate)

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17
Q

compare gravity filtration and vacuum filtration in terms of where the desired product is

A

gravity: filtrate (liquid)
vacuum: precipitate (solid)

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18
Q

what is recrystallization used for?

A

purifying crystals in a solution

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19
Q

how is the solvent for recrystallization used?

A

the product should be soluble in the solvent at high temperatures but insoluble at room temperature.

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20
Q

describe recrystallization

A

as the solution cools, only the desired product will recrystallize out of the solution, excluding impurities

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21
Q

the concept like dissolves like applies to polarity when doing extractions. However, acidic compounds are more dissolved in ____ aqueous solutions.

A

basic

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22
Q

when should distillation be used over separation?

A

distillation is used when the product itself is a liquid that is soluble in the solvent

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23
Q

what does distillation take advantage of?

A

boiling points to separate two liquids

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24
Q

what is the end product of a distillation called?

A

distillate

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25
describe the process of distillation
the liquid with the lower boiling point vaporizes first and the vapors will rise up the distillation column to condense in a water-cooled condenser. This condensate drops down into a vessel with the final product being called the distillate.
26
when is simple distillation used?
used to separate liquids that boil below 150 degrees C and have at least 25 degrees C difference in boiling points prevents degradation of compounds and so the second compound won't boil off into the distillate.
27
what is involved in the set up of a simple distillation?
distilling flask, distillation column (thermometer and condenser), and receiving flask
28
what does a boiling chip, ebulliator, or magnetic stirrer do?
break surface tension and prevent superheating
29
superheating
occurs when a liquid is heated to a temperature above its boiling point without vaporization.
30
superheating occurs when gas bubbles within a liquid are unable to overcome the combination of _____ and _____
atmospheric pressure and surface tension
31
where does water go in and out in condenser
in from bottom and out at top
32
when is vacuum distillation used?
whenever we want to distill a liquid with a boiling point over 150 degrees C
33
what does the vacuum do in vacuum filtration?
lowers the ambient pressure thereby decreasing the temperature that the liquid must reach in order to have sufficient vapor pressure to boil. Distill compounds with higher boiling points at lower temps and do not have to worry about degrading the product.
34
liquids boil when _____
vapor pressure equals ambient pressure
35
when is fractional distillation used?
to separate two liquids with similar boiling points (less than 25 C apart)
36
describe fractional distillation
uses a fractionation column between the distillation flask and the condenser. It is a column with increases surface area. As vapor rises in the column, it condenses and refluxes back down until rising heat makes it evaporate again, only to condense at higher column. Each time the condensate evaporates, the vapor consists of a higher proportion of the compound with the lower boiling point.
37
what is the main concept surrounding chromatography?
the more similar a compound is to its surroundings (whether by polarity, charge, or other characteristics), the more it will stick to and move slowly through it surroundings.
38
what is parititioning
depending on the characteristics of the substances in the sample and the polarity of the mobile phase, it will adhere to the stationary phase with different strengths, causing the different substances to migrate at different speed
39
thin layer chromatography
medium is silica gel or alumina (polar) and the mobile phase is nonpolar spot the sample on the medium, develop the plate by placing it in a beaker in a shallow amount of eluent, solvent moves up the plate and carries the sample with it.
40
paper chromatography
medium is paper cellulose (polar) and the mobile phase is nonpolar spot the sample on the medium, develop the plate by placing it in a beaker in a shallow amount of eluent, solvent moves up the plate and carries the sample with it.
41
column chromatography
uses an entire column which allows for greater separation. uses gravity to move the solvent and compounds down the column can push the solvent faster down using gas (flash column chromatography)
42
gas chromatography (gas-liquid chromatography)
also known as vapor phase chromatography main difference than the other types is that the eluent is gas (usually helium or nitrogen) the absorbent is a crushed polymer inside a 30-foot column kept in an oven to control its temperature the injected compounds must be volatile. mobile phase: gas stationary phase: liquid or solid
43
high-performance liquid chromatography (HPLC)
previously called high pressure liquid chromatography similar to gas chromatography set up but uses a liquid. Computerized so it is highly controlled.
44
in TLC, what moves the solvent up the plate?
capillary action
45
reverse phase chromatography
stationary phase is nonpolar and the mobil phase is polar
46
the retardation factor is ____ for a particular compound in a given solvent
constant
47
what is the formula for the retardation factor?
distance travelled by spot/distance travelled by solvent front
48
can TLC be used to recollect samples?
yes, if not mixed with something to allow them to be seen better, the spots can be scraped off and washed to yield pure products.
49
ion exchange chromatography
the beads in the column are coated with charged substances so that they attract or bind compounds that have an opposite charge
50
what is used to elute charged molecules that have stuck to the column
salt
51
anion exchange chromatography
holds anions using cation beads
52
cation exchange chromatography
holds cations using anion beads
53
size exclusion chromatography
the beads in the column contain tiny pores of varying sizes, slows down smaller compounds. Large compounds cant fit in the pours (moms) so they will move around them and travel through the column faster
54
affinity chromatography
a protein of interest is bound by creating a column with high affinity for that protein. Ex: coat beads with a receptor that binds to that protein
55
affinity chromatography
a protein of interest is bound by creating a column with high affinity for that protein. Ex: coat beads with a receptor that binds to that protein or an antibody
56
what is nickel used for in affinity chromatography
genetically engineered proteins with histidine tags
57
what are problems with washing the column at the end?
the recovered substance could be bound to the eluent that was used to recover it which could be difficult to move
58
In gas chromatography (gas-liquid chromatography), the absorbent is
crushed metal or polymer
59
In gas chromatography (gas-liquid chromatography), the injected compounds must be _____
volatile
60
In gas chromatography (gas-liquid chromatography), the injected compounds must be _____
volatile
61
mass spectrometry
molecular weight determination ionization and fragmentation of compounds, the fragments are run through a magnetic field which separates them by mass to charge ratio
62
why is HPLC used?
it is used if the sample size is small or if forces such as capillary action will affect results.
63
In TLC, decreasing the polarity of the mobile phase will_____ the Rf values
decrease
64
what layer is brine in an extraction?
aqueous layer

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