Ch 12 - Separation and Purification Flashcards
What is extraction?
combines 2 immiscible liquids, one of which easily dissolves the compound of interest
- carried out in a separatory funnel (one phase collected and the solvent is then evaporated)
What is the difference between the aqueous and organic phase in an extraction?
- polar (water) layer is called the aqueous phase and dissolves compounds with hydrogen bonding or polarity
- nonpolar layer is called the organic phase and dissolves nonpolar compounds
What can be used to increase solubility in extraction?
acid-base properties
What is wash?
a reverse of extraction, in which a small amount of solute that dissolves impurities is run over the compound of interest
What is filtration?
isolates a solid (residue) from a liquid (filtrate)
What is the difference between gravity and vacuum filtration?
- gravity: used when the product of interest is in the filtrate; hot solvent is used to maintain solubility
- vacuum: used when the produce of interest is the solid; a vacuum is connected to the flask to pull the solvent through more quickly
What happens in recrystallization?
- the product is dissolved in a minimum amount of hot solvent
- if the impurities are more soluble the crystals will reform while the flak cools, excluding the impurities
What is distillation?
separates liquids according to different boiling points; the liquid with the lowest boiling point vaporizes first and is collected as the distillate
What is simple distillation?
can be used if the boiling points are under 150 C and are at least 25 C apart
What is vacuum distillation?
should be used if the boiling points are over 150 C to prevent degradation of the product
What is fractional distillation?
should be used if the boiling points are less than 25 C apart because allows more refined separation of liquids by boiling point
What do all forms of chromatography use?
2 phases to separate compounds based on physical and chemical properties (based on how strongly they adhere to the solid, or stationary, phase)
What is the difference between the stationary and mobile phase of chromatography?
- stationary (adsorbent) usually a polar solid
- mobile runs through the stationary phase and usually a liquid or gas (this elutes the sample through the stationary phase)
What happens to compounds with higher affinity for the stationary vs mobile phase in chromatography?
- 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
How are compound separated in chromatography?
partitioning
How are thin layer and paper chromatography used to identify a sample?
- stationary phase a polar material (silica, alumina, paper)
- mobile phase 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
What is reverse phase chromatography?
uses a nonpolar card with a polar solvent
What is column chromatography?
utilizes polarity, size, or affinity to separate compounds based on their physical and chemical properties
- the less polar compounds travels most rapidly
What are the stationary and mobile phase of column chromatography?
- stationary is a column containing silica or alumina beads
- mobile is a nonpolar solvent, which travels through the column by gravity
What is ion exchange chromatography?
the beads are coated with charged substances to bind compounds with opposite charges
What is size exclusion chromatography?
the beads have small pores which trap smaller compounds and allow larger compounds to travel through faster
What is 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
What is gas chromatography and its phases?
- separates vaporizable compounds according to how well they adhere to the adsorbent in the column
- stationary is a coil of crushed metal or a polymer
- mobile is a nonreactive gas
What is mass spectrometry?
ionizes and fragments molecules and passes these fragments through a magnetic field to determine molecular weight or structure
What is high performance liquid chromatography (HPLC)?
- similar to column chromatography but uses sophisticated computer-mediated solvent and temperature gradients
- used if the sample size is small or if forces such as capillary action will affect results
- formally called high pressure liquid chromatography
What are the 3 intermolecular forces that affect solubility and how does extraction depend on them?
- H bonding: compounds that can do this, such as alcohols and acids, will move most easily into the aqueous layer
- dipole-dipole interactions: these compounds are less likely to move into the aqueous layer
- van der Waals (London): with only these interactions, compounds are least likely to move into the aqueous layer
What must be true about the 2 solvents used for an extraction to work?
- the 2 solvents must be immiscible and must have different polarity or acid-base properties that allow a compound of interest to dissolve more easily in one than the other
When doing an extraction, would it be better to do 3 extractions with 10 mL of solvent or one extraction with 30 mL?
- better to do 3 washess because more of the compound of interest would be extracted with multiple sequential extractions than one large one
Would acid dissolve better in aqueous acid or base and why?
- acid dissolves better in aqueous base because it will dissociate to form the conjugate base and being more highly charged, will become more soluble
- like dissolves like applies to polarity, acids and bases dissolve more easily in solutions with opposite acid-base characteristics
How is retardation factor (Rf) calculated?
Rf = distance spot moved/distance solvent front moved
