Quiz 2 - Crystallization/Recrystallization/Extractions Flashcards
extraction
technique used to separate a mixture into its individual components via differences in polarity and solubility
polarity
Polarity: distribution of partial charges or electron density throughout a molecule
solubility
- the extent to which a solute will dissolve in a solvent
- “Like dissolves like” rule – relates solubility and polarity
- Like polarities solutes will dissolve in like polarity solvents
miscibility
refers to the interaction between 2 liquids
miscible
similar polarities will appear as one phase when mixed
immiscible
dissimilar polarities will generate 2 layers when mixed
Identify layers using density
typical densities
Halogenated organics > water > non-halogenated organics
***typically aqueous solution is on the bottom BUT cannot assume
solid-liquid extraction
- Separate a mixture of solids by adding a solvent that will dissolve desired solids and leave behind insoluble solids
- Filtration is done to finalize separation
Ex/ mixture of sand and salt
Salt will be dissolved by water through filter paper and sand will remain on top of filter paper
liquid-liquid extraction
- Separate two solutes by using 2 immiscible solvents with opposing polarity
- using a separatory funnel (i.e. our week 3 experiment)
- drain out solution to get desired layer/solution
chemically active extraction
- Separate 2 solutes with similar polarity
*Liquid-liquid extraction will not be effective. - Must make compound prefer water for a solvent by making it more polar via acids/bases protonation/deprotonation
- The charged ion will stay in the aqueous layer and the less polar molecule will separate in the organic layer
Kd
- distribution coefficient that provides a numerical representation of the solubility equilibrium of a given solute in a given solvent system
Kd equation
- Kd = solute organic / solute aqueous
- Kd > 1 → solute prefers organic layer
- Kd < 1 → solute prefers aqueous layer
- Kd = 1 → solute is distributed equally between both layers
most effective extractions?
- Multiple smaller extractions are more effective than one large extraction
overall chemical reaction of week 3 extraction
- mixture in methyl orange is filtered and heated
- insoluble cellulose filtered off
- soluble benzoic acid and methyl orange in organic layer
- NaOH makes benzoic acid negative into benzoate ion
- Benzoate ion is separated into aqueous layer and methyl orange stays in organic layer
- HCl added to reform benzoic acid (impure solid with some MO)
Crystallization
- formation of new, insoluble product by chemical reaction
- This product then precipitates out of the reaction solution as a solid containing many trapped impurities
Recrystallization
- does not involve any chemical reaction
- The crude product is dissolved into solution; conditions are changed that allow crystals to reform
**produces a more pure final product
**can be used as a method to remove impurities
where do impurities come from?
- side products of chemical reactions
- Unreacted starting material
- Contaminants
crystal formation
- When crystals are being formed → the same individual molecules will fit in a specific crystal lattice structure
- Equilibrium process that produces very pure material
- Form quickly ⇒ impurities can become trapped within the crystal lattice resulting in an impure solid
- Form slowly/controlled ⇒ impurities are excluded from the crystal lattice resulting in a pure solid
Extraction of Benzoic Acid Activity
- Extract containing benzoate will contain impurity of methyl orange
- Benzoate ion is soluble in water
- Adding HCl will reform benzoic acid from benzoate (insoluble in water)
- Crystals form too rapidly trapping impurities within growing crystal lattice
***Benzoic acid crystals with methyl orange tapped inside (crude mixture)
recrystallization
- purification method of non-volatile solids
- General technique involves dissolving the solid crystals in a hot solvent and then cooling slowly so pure crystals form
- then filter pure crystals off leaving impurities in solution
When can you use recrystallization ?
- Desired compound is more concentrated than the impurity in the solid material
- Impurity is easily dissolved or not dissolved at all
- Will not be incorporated into the crystal so long as crystal formation is slow
- If the impurities are not dissolved, they can be filtered off
3 stages of solubility
- collision
- dissociation
- solvation
collision
when a solvent (S) molecule collides with the solid crystal surface
Dissociation
- when collision results in the breakaway of a molecule from the solids
***Boiling solvents results in collisions with sufficient energy for dissociation.