Separations and Purifications . *** Flashcards
(27 cards)
extraction
combines two immiscible liquids, one of which easily dissolves the compound of interest.
Polar (water) layer is called the
aqueous phase and dissolves compounds with hydrogen bonding or polarity.
Organic phase
nonpolar layer and dissolves nonpolar compounds.
Extraction is carried out in a
separatory funnel. One phase is collected and the solvent is then evaporated.
acid-base properties can be used to
can be used to increase solubility .
wash
is the reverse of extraction, in which small amounts of solute that dissolves impurities is run over the compound of interest.
Filtration
isolates a solid (residue) from a liquid (filtrate).
gravity filtration
is used when the product of interest is in the filtrate. Hot solvent is used to maintain solubility.
Vacuum filtration
is used when the product of interest is the solid. A vacuum is used when the product of interest is the solid. A vacuum is connected out the flask to pull the solvent through more quickly.
Recrystallization
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.
Distillation
separates liquids according to differences in their boiling points; the liquid with the lowest boiling point vaporizes first and is collected as distillate.
Simple distillation
can be used if the boiling points are under 150 C and are at least 25 C apart.
Vacuum distillation
should be used if the boiling points are over 150 C to prevent degradation of the product.
Fractional distillation
should be used if the boiling points are less than 25 C apart because it allows more refined separation of liquids by boiling points.
Chromatography
use two phases to separate compounds base on physical or chemical properties.
Stationary phase or adsorbent
is usually a polar solid .
Mobile phase
runs through the stationary phase and is usually a liquid or gas. This elutes the sample through the stationary phase.
Compounds with higher affinity for the stationary phase have smaller
retardation factors and take longer to pass through, if at all; compounds with higher affinity for the mobile phase elute through more quickly. Compounds therefore get separated form each other, called partitioning.
Thin layer and paper chromatography
are used to identify a sample:
-stationary phase is polar material, such as silica, alumina, or paper.
-mobile phase is a nonpolar solvent, which climbs the card through capillary action.
-the card is spotted and developed; Rf values can be calculated and compared to reference values.
reverse-phase chromatography uses a nonpolar card with a polar solvent.
column chromatography
utilizes polarity, size or affinity to separate compounds based on their physical or chemical properties.
- stationary phase is column containing silica or alumina beads.
- mobile phase is a a nonpolar solvent, which travels through the column by gravity.
Ion-exchange chromatography
beads are coated with charged substances to bind to compounds with opposite charge.
size-exclusion chromatography .
beads have small pores which trap smaller compounds and allow larger compounds to travel through faster.
affinity chromatography
the column is made to have high affinity for a compound by coating the beads with a receptor or antibody to the compound.
Gas chromatography
separates vaporizable compounds according to how well they adhere to the adsorbent in the column.
- stationary phase is a coil of crushed metal or a polymer
- the mobile phase is a nonreactive gas
- gas chromatography may be convinced in sequence with mass spectrometry, which ionizes and fragments molecules and passes these fragments through a magnetic field to determine molecular weight or structure.
