ch 12 - Separations and Purifications Flashcards Preview

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Flashcards in ch 12 - Separations and Purifications Deck (20)
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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



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


three intermolecular forces that affect solubility

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


simple distillation

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


vacuum distillation

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


fractional distillation

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



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


process of chromatography

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



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


thin-layer chromatography

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


reverse-phase chromatography

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


retardation factor

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


preparative TLC

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


column chromatography

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


ion-exchange chromatography

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


size-exclusion chromatography

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)


affinity chromatography

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


Gas chromatography (GC)

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)


mass spectrometry

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


high-performance liquid chromatography

(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