Separations and Purifications Flashcards
What is extraction?
the transfer of a dissolved compound (the desired product) from a starting solvent into a solvent in which the product is more soluble
What fundamental concept is extraction based on?
like dissolves like
How does extraction work?
(1) Mix two immiscible solvents together - one which has the desired product in it
(2) One of the layers will be aqueous phase (generally water; generally bottom layer) and the other will be organic phase (generally top layer)
(3) If the desired product is polar like water, it will mix more with water and separate out with the water layer and vice versa
(4) Repeat this mixing and draining process with water a few times to extract all of the desired product
(5) Obtain end result by evaporating the water
What is a wash?
a small amount of solute is used to extract and remove impurities, rather than the compound of interest; reverse of the typical extraction method
What is filtration?
isolates a solid from a liquid
What are the types of filtration and their purposes?
Gravity filtration - using solvents own weight to pull through filter; focuses on isolating filtrate
Vacuum filtration - using vacuum connected to a flask; focuses on isolating solid
What is recrystallization?
a method for further purifying crystals in a solution
How does recrystallization work?
(1) Dissolve the desired product in minimum amount of solvent
(2) Solvent + Product must only be able to dissolve at high temperatures
(3) When the mixture is cooled down, the product will crystallize out and the impurities will be stuck in the solvent solution bc they are still soluble at lower temps
What is distillation?
takes advantages of differences in boiling points to separate two liquids by evaporation and condensation
What is simple distillation?
(1) Liquid with the lower boiling points will vaporize first
(2) Vapors rise and cool in a condenser and go back to liquid form but separated now
(3) Liquids must boil below 150C and have at least a 25 C difference between boiling points
What is superheating?
occurs when a liquid is heated to a temperature above its boiling point without vaporization
What is vacuum distillation?
used when boiling point is over 150C
(1) Adding a vacuum lowers the pressure and decreases the temperature that the liquid boils at
(2) No worries about degrading the product
What is fractional distillation?
used for when the two compounds are less than 25C apart in boiling points
(1) Uses a fractional distillation column that is filled with glass beads or steel wool to increase surface area
(2) Vapor rises and as it cools it condenses on the inner packing
(3) This process is repeated and each time the vapor rises it condenses on a higher portion of the column
(4) Eventually it reaches the top and filters into a collection tube
What is thin-layer chromatography? or paper?
TLC - uses a sheet coated in a thin layer of silica gel/alumina (polar;hydrophilic)
(1) The sample is placed in a dot on the sheet
(2) A jar is filled with a layer of solvent/eluent
(3) The sheet is placed in the jar with only the bottom bit submerged in the solution
(4) The eluent will move up the sheet and pull the samples with it
Polar molecules stick to gel and nonpolar move up quicker
How does chromatography work?
There are two phases: stationary and mobile
(1) The sample is placed on the stationary phase and the mobile phase/solution (usually liquid) is run over the stationary phase
(2) The mobile phase moves the sample through the stationary phase
(3) The sample will migrate at a specific speed depending on its properties
