Quiz 4 - Experiments 3-6 Flashcards
Define Thin Layer Chromatography
Common technique used in which compounds are separated so they can be seen even if they are part of a mixture
What are the benefits of using Thin Layer Chromatography?
- Inexpensive
- Very little sample required
- Numerous samples can be tested at once
- Samples can be recovered if necessary
TLC is specifically popular for determine when a reaction is ____________ by the appearance of the __________ and the disappearance of the __________ __________.
Complete; product; starting material(s)
When doing a TLC experiment, one of the keys to success is spotting the samples at a level that is…
HIGHER than the solvent in the chamber
Why is it important for the spotting samples to be higher than the level of solvent in the chamber?
Allows the spot to travel up the plate rather than dilute it down into the solvent
What is the most common method for visualizing TLC plates?
Utilizing UV lamps is used to illuminate the plate in order to visualize the spots
What is utilized to visualize TLC plates when UV light is insufficient?
Iodine vapor
What is the equation for obtaining Rf values?
Rf = distance compound/distance solvent
What does Rf stand for?
Retention factor
The reason that compounds have different Rf values is due to ___________.
Polarity
What are the many ways the polarity of a molecule can be measured?
- TLC (chromatography method)
- GC (chromatography method)
- Dipole moment
- Dielectric constant
Least polar compounds are often found to be…
Hydrocarbons
Most polar compounds are often found to be…
Compounds that have N/O-H and C=O (polar) bonds
TLC experiments have 3 important factors that must be considered when making generalization about the behavior of the solutes being analyzed…
I) Polarity of solid support
II) Polarity of the solvents used to develop the plate
III) Polarity of compound/solute itself
The polarity of the solid support (silica or alumina) = ___________ phase.
Immobile
The polarity of the solvent(s) used to develop the plate = ___________ phase.
Mobile
In TLC, the silica gel found on the plates is very ________.
Polar
As the solvent travels up a TLC plate, the sample molecules must decide if they want to…
Adhere to the plate or move with the solvent
In general, polar compounds tend to do what on the polar silica gel?
Tend to “stick” on the polar silica gel
In general, nonpolar compounds tend to do what on the polar silica gel?
Tend to prefer the solvent
Typically on TLC run on silica gel slides/plates, non-polar compounds generally have __________ Rf values than polar compounds.
HIGHER
Specific Rf values are dependent upon…
The polarity of the solid support and developing solvent
More polar developing solvent attract…
Polar organic compounds away from the silica gel and carry them farther up the plate
Traveling higher up a TLC plate will result in a ___________ Rf value.
Higher
Less polar developing solvents give ___________ Rf values.
Lower
Since separation of compounds is sometimes difficult, it is common to use __________ as developing solvents so the polarity can be controlled.
Mixtures
In TLC what will happen if the initial spot is very large when preparing the plate?
Your results could end up with a very poor resolution and lead to inaccurate measurements
In TLC what will happen if the initial spot is below the level of the solvent in the developing chamber?
The result could be that rather than getting separate results the spot would merge into the solvent
One measure of solvent polarity is the __________ ________.
Dielectric constant
Organic solvents tend to have _________ Dielectric Constants.
LOWER
In experiment 4, when isolating caffeine, the top layer is the __________ layer and the bottom layer is the __________ layer.
Aqueous; DCM
Cellulose _______ dissolve well in DCM.
DOESN’T
The more acidic something is the __________ the precipitation.
HIGHER
Define Recrystallization
The most common method for purifying solid organic compounds
How do you use Recrystallization to test for purity of a compound?
After recrystallization, when crystals are collected and dried, the samples are tested for purity by comparing their melting point with literature reported melting point values.
What macroscopic factors can come into play when it comes to isolating pure crystals?
- Temperature
- Pressure
- Absolute humidity
Define Polymorphs
The different crystalline phases an organic compound can be in
T/F Within Polymorphs the arrangements and conformations of a molecule in the crystal lattice can’t change
False; the arrangements and conformations of the molecule in the crystal lattice can change
Pure pharmaceutical compounds can typically be grouped into 3 categories…
I) Amorphous solids
II) Solvates
III) Hydrates
Define Amorphous Solids
Do not have an ordered arrangement of molecules and do not have a distinguishable crystal lattice
Define Solvates
Has a solvent incorporated into the crystal lattice
T/F It is not common to find one polymorph having a higher M.P. than the other
False; it is common to find one polymorph having a higher M.P. than the other
Is it common or uncommon for the same polymorph of SST to show different M.P.
It is uncommon and considered an error for the M.P. for the same polymorph of SST to be higher than the other value
What could be the reason being the same polymorph of SST to show different M.P.s
Result of heating the solution too rapidly
What could be the result of a lower found M.P.
Could be the result of contaminants present
What are potential contaminants of SST?
- Sulfathiazole
- Sulfanilamide
- Succinic Acid
What are 4 experimental factors that should be considered when attempting to isolate polymorphic forms of a solid pure substance?
I) Temperature
II) Pressure
III) Absolute Humidity
IV) Type of Solvent
Define Steam Distillation
Process of co-distilling a compound with water
Steam Distillation takes advantage of the…
Insolubility of most oil-like organic compounds in water
Steam Distillation provides a route for separating…
Lower boiling (insoluble) compounds from higher boiling organic compounds or physical/plant matter
Steam Distillation of an immiscible liquid mixture results in…
Each component of the immiscible mixture contributes to the total vapor pressure as if the other were not present
Total vapor pressure = …
Sum of the vapor pressure of water + vapor pressures of each of the organic components in the mixture
Define Dalton’s Law of Partial Pressures
States that the total vapor pressure of the mixture is always GREATER than the individual vapor pressures of the liquids in the mixture.
Boiling point of a liquid is ___________ proportional to the vapor pressure.
Inversely
The boiling point of a mixture of immiscible liquids must be ___________ than that of the lowest boiling component.
Lower
A liquid or liquid mixture boils when the total vapor pressure of the liquid is equal to…
Atmospheric pressure
The presence of any immiscible organic material contributes to the total vapor pressure in what way?
Causes the boiling point of water to drop below 100 degrees Celsius
