Experiment#3: Recrystallization Flashcards
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
PROCESS OF RECRYSTALLIZATION
This employs a vacuum to hasten the passage of filtrate through the filter paper.
Suction Filtration
PROCESS OF RECRYSTALLIZATION
What is Suction Filtration also known as?
Vacuum Filtration
PROCESS OF RECRYSTALLIZATION
The name of the porous funnel used in Suction Filtration.
Buchner Funnel
PROCESS OF RECRYSTALLIZATION
The name of the flask used in Suction Filtration.
Suction Flask
PROCESS OF RECRYSTALLIZATION
What are the 4 different solvents to choose from in the experiment?
- Water
- Ethanol
- Benzene
- Ethyl Acetate
PROCESS OF RECRYSTALLIZATION
What compound do we use in the Recrystallization experiment?
Acetanilide
PROCESS OF RECRYSTALLIZATION
Which of the 4 aforementioned solvents do we eventually end up using in the experiment?
Water, since the acetanilide - once dissolved - is insoluble in room temperature, soluble when heated, and insoluble/crystallizes when cooled.
TRUE or FALSE | PROCESS OF RECRYSTALLIZATION
Adding activated carbon while the solution is boiling will cause it to boil over.
TRUE
PROCESS OF RECRYSTALLIZATION
What do we call a substance after it has been filtered?
Filtrate
PROCESS OF RECRYSTALLIZATION
In Suction Filtration, what a) ends up inside the suction flask and what b) ends up left behind on top of the Buchner funnel?
A) Filtrate (Solvent and Impurities)
B) Recovered Acetanilide
PROCESS OF RECRYSTALLIZATION
If the initial mass of impure acetanilide is 3.506 g and the mass of the recrystallized acetanilide is 1.006 g, what is the percent recovery?
28.69%
[% Recovery = (mass of recrystallized solid/mass of crude sample)x100]
= (1.006/3.506)x100 = 28.69%
