separations - answer-a variety of lab techniques that use intermolecular forces to separate a mixture into its component parts; can be separated according to solubility, melting point, boiling point, or any other physical property
main types: extraction, distillation, crystallization, and chroma...
Laboratory Techniques
separations - answer-a variety of lab techniques that use intermolecular forces to
separate a mixture into its component parts; can be separated according to solubility,
melting point, boiling point, or any other physical property
main types: extraction, distillation, crystallization, and chromatography
extraction - answer-a separation technique based on solubility; involves two phases,
most commonly the aqueous layer and the less dense organic mixture
What are the steps to performing an extraction? - answer-1. Add weak acid; acid
protonates strong bases; makes them polar and they move to aqueuos layer and strong
bases are removed.
2. Add strong acid; weak bases removed.
3. Add weak base; strong acids removed.
4. Add strong base; weak acids removed.
distillation - answer-technique used to separate compounds that have significantly
different boiling points; liquids with boiling point differences of at least 20C can be
separated by slow boiling; the compound with lower BP boils off first
fractional distillation - answer-more precise method of distillation that can be used to
separate liquids whose boiling points are fairly close together
vapor is run through glass beads, allowing the compound with the higher boiling point to
repeatedly condense and fall back into the solution
crystallization - answer-based on the principle that pure substances form crystals more
easily than impure substances; very inefficient method of separation difficult to arrive at
a pure substance; exothermic process
chromatography - answer-used to purify a compound from a mixture and/or to identify
the ratio of compounds in a mixture; separation of a mixture by passing it over or
through a matrix that absorbs (binds) different compounds more or less strongly
according to their properties
mobile phase - answer-mixture is dissolved into a solution that passes through
stationary phase - answer-matrix surface (solid surface usually) that adsorbs
compounds from the mixture
Which compounds move more slowly? - answer-those that have a greater affinity for the
surface; usually polar compounds
, column chromatography - answer-a solution containing the mixture is dripped down a
column containing the solid phase (usually glass beads); more polar compounds travel
slowly, creating separate layers
high pressure liquid chromatography (HPLC) - answer-the column and solution use an
apparatus that puts the system under high pressure
paper chromatography - answer-a small portion of the sample to be separated is
spotted onto paper; one end of the paper is then placed into a nonpolar solvent; as the
solvent moves up the paper, more polat components of the sample move more slowly
because they are attracted to the polar paper
--> less polar components dissolve more easily to move up the paper with the solvent
Rf factor - answer-can be calculated for each component in paper chromatography -->
divide the distance traveled by the component by the distance traveled by the solvent
non-polar components --> Rf close to 1
polar components --> lower Rf factor
thin-layer chromatography - answer-similar to paper chromatography; coated glass or
plastic plate is used instead of paper; the results are visualized via an iodine vapor
chamber
gas-liquid chromatography - answer-the liquid phase is the stationary phase; the
mixture is dissolved into a heated carrier gas and passed over a liquid phase bound to a
column; compounds in the mixture equilibrate with the liquid phase at different rates and
pass through an exit port as individual components
size-exclusion chromatography - answer-well suited for peptides and proteins;
molecules are separated by their SIZE and sometimes their MOLECULAR WEIGHT,
often through gel filtration
ion-exchange chromatography - answer-molecules are separated based on their net
surface charge; utilizes cationic or anionic "exchangers" that slow down the movement
of charged molecules
affinity chromatography - answer-uses highly specific interactions to slow down select
molecules; can make use of receptor-ligand, enzyme-substrate, and antigen-antibody
interactions
gel electrophoresis - answer-mixtures of amino acids (DNA and RNA fragments) or
mixtures of proteins/polypeptides can be separated based on size and charge; the
molecular mixture is placed in a gel and an electric field is applied
larger particles move more slowly
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