Experiment#3: Recrystallization
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RECRYSTALLIZATION Enumerate the 4 requirements a solvent must have.
• Low BP, so oiling out doesn’t occur. • Volatile, so the solvent can be vaporized from the sample. • Chemically Inert - solvent must not decompose or oxidize the substance. • Unreactive with the solute.
The deposition of crystals from a solution.
Crystallization
Common method used to purify organic compounds that are solid at room temperature.
Crystallization
CRYSTALLIZATION During crystallization, why is it that molecules have the tendency to be attached to a growing crystal composed with the same type of molecules?
Because they fit better in the molecule’s crystal lattice.
A fixed and rigid arrangement of atoms, molecules or ions.
Lattice Structure
LATTICE STRUCTURE In each unit cell, there are 8 spheres at each end of a three-dimensional cube that represent an atom, ion, or molecule. What are these spheres called?
Lattice Point
LATTICE STRUCTURE Repeating unit cells form the ______ ______ of a crystalline solid.
Lattice Structure
RECRYSTALLIZATION What 2 factors does Recrystallization take advantage of being that it is a common method of purifying organic substances from the traces of foreign substances?
1) The difference in solubility at different temperatures and, 2) The tendency of a growing crystal to exclude anything that does not fit into its lattice.
The maximum amount of solute that dissolves in a given volume of solvent at a given temperature.
Solubility
RIGHT or WRONG | SOLUBILITY NaCl - 100 mL water/35.9 g at 25 °C Is this unit of solubility correct?
WRONG. The unit for solubility is grams of solute/mL of solvent meaning if we were to correct this, it would be: NaCl - 35.9g/100 mL water at 25 °C
SOLUBILITY The one to be dissolved.
Solute
SOLUBILITY The one used to dissolve.
Solvent
SOLUBILITY What is the unit for solubility?
grams of solute/mL of solvent
A solvent that shows the desired solubility behavior for the substance to be crystallized.
Recrystallizing Solvent
RECRYSTALLIZING SOLVENT What are the 3 requirements in picking a solvent for the experiment?
• INSOLUBLE at Room Temperature • SOLUBLE when Heated • INSOLUBLE/CRYSTALLIZES when Cooled
TRUE OR FALSE | RECRYSTALLIZATION Unwanted impurities should be soluble at room temperature or insoluble during heating.
TRUE
PROCESS OF RECRYSTALLIZATION If there are colored impurities, what is added to the hot solution?
Activated Carbon
PROCESS OF RECRYSTALLIZATION If crystallization does not happen, what 3 things can be done in order to promote crystal growth?
1) Scratching the inside surface of the glass vessel 2) Adding in a ”seed” crystal of the compound 3) Dipping a glass rod in the solution, aerating it to dry off the solvent before returning the rod to the solution
PROCESS OF RECRYSTALLIZATION Enumerate the first 3 steps of Recrystallization.
1) Selection of Solvent 2) Dissolution of crystal in the solvent 3) Filtration of the hot mixture
PROCESS OF RECRYSTALLIZATION Enumerate the last 2 steps of Recrystallization.
4) Slow cooling to allow crystallization 5) Removal of soluble impurities
PROCESS OF RECRYSTALLIZATION Performed to separate insoluble impurities from the hot solution of the compound.
Hot Gravity Filtration
PROCESS OF RECRYSTALLIZATION Why is it a requirement for Hot Gravity Filtration to be done as rapidly as possible?
To avoid premature recrystallization on the funnel.
PROCESS OF RECRYSTALLIZATION Used to maximize the flow rate during the filtration because of its larger surface area.
Fluted Filter Paper
PROCESS OF RECRYSTALLIZATION Used to minimize clogging during filtration.
Short-stemmed Funnel