Chapter 12- Separations and Purifications Flashcards
extraction
transfer of a dissolved compound (the desired product) from a starting solvent into a solvent in which the product is more soluble. based on “like dissolves like”
-requires two IMMISCIBLE solvents (they do not mix)
what forms during an extraction
- aqueous phase (layer)- typically more dense and on bottom of funnel
- organic phase (layer)- typically less dense and on top of funnel
-use a separatory funnel to isolate these two phases
what are the 3 intermolecular forces that affect solubility
- hydrogen bonding- compounds that can do this will be in the aqueous layer
- dipole-dipole interactions- likely to be in the organic layer
- Van der Waals (London) forces- most likely to be in the organic layer
rotary evaporator (rotovap)
used at the end of an extraction where the solvent is evaporated leaving the product alone
gravity filtration vs. vacuum filtration
gravity filtration: used when product of interest is in the filtrate, hot solvent is used to keep the product dissolved in the liquid
vacuum filtration: solvent is forced through the filter by a vacuum connected to the flask, more often used when solid is the desired product.
recrystallization
further purifying crystals in solution. needs solvent where the product is soluble only at high temps so when it recrystallizes only the actual product crystallizes.
distillation
takes advantage of differences in boiling point to separate two liquids by evaporation and condensation (used in distillery to make liquor b/c ethanol boils at a lower temperature than water)
when do liquids boil
when their vapor pressure equals ambient pressure
what type of distillation is used when…
simple: liquids that boil below 150C and have at least 25C difference in boiling points
vacuum: liquids with boiling point over 150C
fractional: liquids with similar boiling points less than 25C apart (uses an upright/vertical column)
chromatography
uses physical and chemical properties to separate and identify compounds from a complex mixture.
-the more similar a compound is to its surroundings (polarity, charge, etc.), the more it will stick to and move slowly through its surroundings.
4 types of chromatography
- thin-layer and paper chromatography
- column chromatography
- gas chromatography
- high-performance liquid chromatography (HPLC)
-typically on MCAT polarity is used to separate substances from each other
thin-layer chromatography and paper chromatography AND reverse-phase chromatography
TLC: thin layer of silica gel or alumina adherent to an inert carrier sheet is used for the stationary phase (polar hydrophilic gel used)
Paper: piece of paper made of cellulose is used for the stationary phase
- sample spots creep up the plate by capillary action, carrying the various compounds in the sample with it at varying rates.
- reverse-phase chromatography is the exact opposite where the stationary phase is nonpolar
retardation factor (Rf)
distance spot moved / distance solvent front moved
-value is relatively constant so it can be used to identify unknown compounds
3 types of column chromatography
- ion-exchange: beads in column are coated with charged substance so they attract or bind compounds that have an opposite charge
- size-exclusion: beads in column have tiny pores of varying sizes so the smaller molecules will take longer to get to the bottom because they have more to go through to get to the bottom
- affinity: protein of interest is bound by creating a column with high affinity for that protein by coating the beads with receptor that binds the protein. what you want ends up staying in the column. then after only the protein is left it can be eluted by washing the column
gas chromatography
aka. vapor-phase chromatography (VPC).
the eluent is a gas instead of a liquid
- injecting compounds must be volatile: low melting point, sublimable solids, vaporizable liquids
- usually the pure molecules go into a mass spectrometer for molecular weight determination
