ch 12 - Separations and Purifications

Question 1

extraction

Answer 1

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

Question 2

immiscible

Answer 2

referring to solvents, meaning two that form two layers and do not mix (like water and oil)

Question 3

three intermolecular forces that affect solubility

Answer 3

hydrogen bonding (compounds that do this will move more easily into the aqueous layer), dipole-dipole interactions (compounds are less likely to move into the aqueous layer), and van der Waals or London forces (with only these interactions, compounds are less likely to move into the aqueous layer

Question 4

simple distillation

Answer 4

used for liquids that boil below 150 C and have at least a 25 C difference between the two boiling points

Question 5

vacuum distillation

Answer 5

used for liquids with boiling points above 150 C. vacuum lowers ambient pressure and allows liquid to boil at lower temp than usual

Question 6

fractional distillation

Answer 6

used to separate two liquids with similar boiling points (less than 25 C apart)

Question 7

chromatography

Answer 7

tool that uses physical and chemical properties to separate and identify compounds from a complex mixture: 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 its surroundings

Question 8

process of chromatography

Answer 8

sample goes into stationary phase (adsorbent), then mobile phase (liquid or gas in gas chromatography) is run through stationary phase which displaces (elutes) sample and carries it through the stationary phase. Different substances will migrate at different speeds based on characteristics and polarity of the mobile phase

Question 9

partitioning

Answer 9

process in which substances elute at different speeds and are able to be separated according to their partitioning coefficients during chromatography

Question 10

thin-layer chromatography

Answer 10

very similar to paper chromatography: vary only in the medium used for stationary phase; thin-layer uses thin layer of silica gel or alumina adherent to an inert carrier sheet; the more nonpolar the sample is the further up the polar stationary phase it will move as the eluent is weak or moderately polar

Question 11

reverse-phase chromatography

Answer 11

opposite of thin-layer chromatography in that the stationary phase is nonpolar so nonpolar samples will move slowly and polar ones will move quickly

Question 12

retardation factor

Answer 12

calculation by which compounds are generally identified when TLC is performed: R sub f = distance spot moved/distance solvent front moved

Question 13

preparative TLC

Answer 13

TLC used on a larger scale as a means of purification; as large plate develops, the larger spot of sample splits into bands of individual compounds, which can then be scraped off and washed to yield pure compounds

Question 14

column chromatography

Answer 14

same concept as TLC except with a column that is filled with gel silica or aluminum beads as an adsorbent and uses gravity to move the solvent down the column

Question 15

ion-exchange chromatography

Answer 15

type of column chromatography; beads in column are coated with charged substances so that they attract or bind compounds that have an opposite charge; after all other compounds have moved through the column, salt gradient is used to elute the charge molecules that have stuck to the column

Question 16

size-exclusion chromatography

Answer 16

type of column chromatography; beads used in the column contain tiny pores of varying sizes which allow small compounds to enter the beads, slowing them down (may be counterintuitive)

Question 17

affinity chromatography

Answer 17

type of column chromatography; protein of interest is bound by creating a column with high affinity for that protein; can be done by coating beads with receptor that binds the protein or antibody to the protein; in both cases, protein is retained in the column; substance may become bound to eluent making it difficult to remove

Question 18

Gas chromatography (GC)

Answer 18

also called vapor-phase chromatography (VPC); method that can be used for qualitative separation; difference between this and other forms is that eluent is a gas; adsorbent is a crushed metal or polymer inside a 30 foot column; injected compounds much be volatile (low-melting point, sublimable solids or vaporizable liquids)

Question 19

mass spectrometry

Answer 19

often used to determine weight of pure molecules injected into a mass spectrometer after gas chromatography is performed; involves the ionization and fragmentation of compounds. fragments are then run through a magnetic field separating them by mass-to-charge ratio; weight or relative concentrations of the fragments can be determined or calculated and compared against reference values to identify the compound

Question 20

high-performance liquid chromatography

Answer 20

(HPLC) eluent is a liquid; higher performance because the entire process is computerized; liquid travels through a column of defined composition; contents injected into column and separation occurs as it flows through. compounds pass through a detector and are collected as the solvent flows out the end