Separations and Purifications

Question 1

combines two immiscible liquids, one of which easily dissolves the compound of interest; carried out in a separatory funnel; one phase is collected, and then the solvent is evaporated

Answer 1

extraction

Question 2

extraction:
the polar (water) layer; dissolves compounds with hydrogen bonding or polarity

Answer 2

aqueous phase

Question 3

extraction:

the nonpolar layer; dissolves nonpolar compounds

Answer 3

organic phase

Question 4

a small amount of solvent that dissolves impurities is run over the compounds of interest; the reverse of extraction

Answer 4

wash

Question 5

isolates a solid (residue) from a liquid (filtrate)

Answer 5

filtration

Question 6

filtration:

is used when the product of interest is in the filtrate; hot solvent is used to maintain solubility

Answer 6

gravity filtration

Question 7

filtration:
is used when the product of interest is the solid (residue); a vacuum is connected to the flask to pull the solvent through more quickly

Answer 7

vacuum filtration

Question 8

the product is dissolved in a minimum amount of hot solvent; if the impurities are more soluble, the crystals will reform while the flask cools, excluding the impurities

Answer 8

recrystallization

Question 9

separates liquids according to differences in their boiling points; the liquid with the lowest boiling point vaporizes first and is collected as the distillate

Answer 9

distillation

Question 10

distillation:

can be used if the boiling points are under 150ºC and are at least 25ºC apart

Answer 10

simple distillation

Question 11

distillation:
should be used if the boiling points are over 150ºC to prevent degradation of the product; pressure is decreased which allows the liquid to boil at a lower temperature

Answer 11

vacuum distillation

Question 12

distillation:
should be used if the boiling points are less than 25ºC apart because it allows more refined separation of liquids by boiling point; uses a fractionation column to increase surface area to allow more cycles of evaporation and condensation

Answer 12

fractional distillation

Question 13

uses two phases to separate compounds based on physical or chemical properties

Answer 13

chromatography

Question 14

chromatography:

usually a polar solvent

Answer 14

stationary phase (absorbent)

Question 15

chromatography:

runs through the stationary phase and is usually a liquid or a gas; this elutes the sample through the stationary phase

Answer 15

mobile phase

Question 16

chromatography:

separation of compounds from each other due to differences in affinity for the stationary phase

Answer 16

partitioning

Question 17

chromatography:
value used to identify unknown compounds; smaller in compounds with higher affinity for stationary phase, and larger in compounds with lower affinity for stationary phase

Answer 17

retardation factor (R(f))

Question 18

retardation factor (R(f))

Answer 18

R(f) = distance spot moved / distance solvent front moved

Question 19

chromatography technique:
two similar techniques, that differ only in the medium used for the stationary phase; a card (stationary phase) is spotted and developed; R(f) values can be calculated and compared to reference values

Answer 19

thin-layer chromatography (TLC) and paper chromatography

Question 20

thin-layer chromatography (TLC) and paper chromatography:

is a polar material, such as silica (TLC), alumina (TLC), or paper (paper(cellulose))

Answer 20

stationary phase

Question 21

thin-layer chromatography (TLC) and paper chromatography:

is a nonpolar solvent, which climbs the card (stationary phase) through capillary action

Answer 21

mobile phase

Question 22

thin-layer chromatography (TLC) and paper chromatography:
same technique as TLC and paper, but the card (stationary phase) is nonpolar and the solvent is polar, so polar molecules move up quickly and nonpolar more slowly

Answer 22

reverse-phase chromatography

Question 23

chromatography technique:
utilizes polarity, size, or affinity to separate compounds based on their physical or chemical properties; uses an entire column filled with silica or alumina beads as an absorbent, allowing for much greater separation

Answer 23

column chromatography

Question 24

column chromatography:

is a column containing silica or alumina beads

Answer 24

stationary phase

Question 25

column chromatography:

is a nonpolar solvent, which travels through the column by gravity

Answer 25

mobile phase

Question 26

column chromatography:

the beads are coated with charged substances to bind compounds with opposite charge

Answer 26

ion-exchange chromatography

Question 27

column chromatography:

the beads have small pores which trap smaller compounds and allow larger compounds to travel through faster

Answer 27

size-exclusion chromatography

Question 28

column chromatography:

the column is made to have high affinity for a compound by coating the beads with a receptor or antibody to the compound

Answer 28

affinity chromatography

Question 29

chromatography technique:

separates vaporizable compounds according to how well they adhere to the absorbent in the column

Answer 29

gas chromatography (GC)

Question 30

gas chromatography (GC):
is a coil of crushed metal or a polymer

Answer 30

stationary phase

Question 31

gas chromatography (GC):
is a nonreactive gas

Answer 31

mobile phase

Question 32

gas chromatography (GC):
often used in sequence with GC to determine molecular weight; ionizes and fragments molecules and passes them through a magnetic field to determine molecular weight or structure

Answer 32

mass spectrometry

Question 33

is similar to column chromatography but uses sophisticated computer-mediated solvent and temperature gradients; it is used if the sample size is small or if forces such as capillary action will affect results

Answer 33

high-performance liquid chromatography (HPLC)