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Organic Chemistry Lab (Serena) > Quiz 4 - Experiments 3-6 > Flashcards

Quiz 4 - Experiments 3-6 Flashcards

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1
Q

Define Thin Layer Chromatography

A

Common technique used in which compounds are separated so they can be seen even if they are part of a mixture

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2
Q

What are the benefits of using Thin Layer Chromatography?

A
  • Inexpensive
  • Very little sample required
  • Numerous samples can be tested at once
  • Samples can be recovered if necessary
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3
Q

TLC is specifically popular for determine when a reaction is ____________ by the appearance of the __________ and the disappearance of the __________ __________.

A

Complete; product; starting material(s)

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4
Q

When doing a TLC experiment, one of the keys to success is spotting the samples at a level that is…

A

HIGHER than the solvent in the chamber

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5
Q

Why is it important for the spotting samples to be higher than the level of solvent in the chamber?

A

Allows the spot to travel up the plate rather than dilute it down into the solvent

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6
Q

What is the most common method for visualizing TLC plates?

A

Utilizing UV lamps is used to illuminate the plate in order to visualize the spots

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7
Q

What is utilized to visualize TLC plates when UV light is insufficient?

A

Iodine vapor

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8
Q

What is the equation for obtaining Rf values?

A

Rf = distance compound/distance solvent

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9
Q

What does Rf stand for?

A

Retention factor

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10
Q

The reason that compounds have different Rf values is due to ___________.

A

Polarity

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11
Q

What are the many ways the polarity of a molecule can be measured?

A
  • TLC (chromatography method)
  • GC (chromatography method)
  • Dipole moment
  • Dielectric constant
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12
Q

Least polar compounds are often found to be…

A

Hydrocarbons

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13
Q

Most polar compounds are often found to be…

A

Compounds that have N/O-H and C=O (polar) bonds

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14
Q

TLC experiments have 3 important factors that must be considered when making generalization about the behavior of the solutes being analyzed…

A

I) Polarity of solid support
II) Polarity of the solvents used to develop the plate
III) Polarity of compound/solute itself

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15
Q

The polarity of the solid support (silica or alumina) = ___________ phase.

A

Immobile

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16
Q

The polarity of the solvent(s) used to develop the plate = ___________ phase.

A

Mobile

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17
Q

In TLC, the silica gel found on the plates is very ________.

A

Polar

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18
Q

As the solvent travels up a TLC plate, the sample molecules must decide if they want to…

A

Adhere to the plate or move with the solvent

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19
Q

In general, polar compounds tend to do what on the polar silica gel?

A

Tend to “stick” on the polar silica gel

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20
Q

In general, nonpolar compounds tend to do what on the polar silica gel?

A

Tend to prefer the solvent

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21
Q

Typically on TLC run on silica gel slides/plates, non-polar compounds generally have __________ Rf values than polar compounds.

A

HIGHER

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22
Q

Specific Rf values are dependent upon…

A

The polarity of the solid support and developing solvent

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23
Q

More polar developing solvent attract…

A

Polar organic compounds away from the silica gel and carry them farther up the plate

24
Q

Traveling higher up a TLC plate will result in a ___________ Rf value.

A

Higher

25
Q

Less polar developing solvents give ___________ Rf values.

A

Lower

26
Q

Since separation of compounds is sometimes difficult, it is common to use __________ as developing solvents so the polarity can be controlled.

A

Mixtures

27
Q

In TLC what will happen if the initial spot is very large when preparing the plate?

A

Your results could end up with a very poor resolution and lead to inaccurate measurements

28
Q

In TLC what will happen if the initial spot is below the level of the solvent in the developing chamber?

A

The result could be that rather than getting separate results the spot would merge into the solvent

29
Q

One measure of solvent polarity is the __________ ________.

A

Dielectric constant

30
Q

Organic solvents tend to have _________ Dielectric Constants.

A

LOWER

31
Q

In experiment 4, when isolating caffeine, the top layer is the __________ layer and the bottom layer is the __________ layer.

A

Aqueous; DCM

32
Q

Cellulose _______ dissolve well in DCM.

A

DOESN’T

33
Q

The more acidic something is the __________ the precipitation.

A

HIGHER

34
Q

Define Recrystallization

A

The most common method for purifying solid organic compounds

35
Q

How do you use Recrystallization to test for purity of a compound?

A

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.

36
Q

What macroscopic factors can come into play when it comes to isolating pure crystals?

A
  • Temperature
  • Pressure
  • Absolute humidity
37
Q

Define Polymorphs

A

The different crystalline phases an organic compound can be in

38
Q

T/F Within Polymorphs the arrangements and conformations of a molecule in the crystal lattice can’t change

A

False; the arrangements and conformations of the molecule in the crystal lattice can change

39
Q

Pure pharmaceutical compounds can typically be grouped into 3 categories…

A

I) Amorphous solids
II) Solvates
III) Hydrates

40
Q

Define Amorphous Solids

A

Do not have an ordered arrangement of molecules and do not have a distinguishable crystal lattice

41
Q

Define Solvates

A

Has a solvent incorporated into the crystal lattice

42
Q

T/F It is not common to find one polymorph having a higher M.P. than the other

A

False; it is common to find one polymorph having a higher M.P. than the other

43
Q

Is it common or uncommon for the same polymorph of SST to show different M.P.

A

It is uncommon and considered an error for the M.P. for the same polymorph of SST to be higher than the other value

44
Q

What could be the reason being the same polymorph of SST to show different M.P.s

A

Result of heating the solution too rapidly

45
Q

What could be the result of a lower found M.P.

A

Could be the result of contaminants present

46
Q

What are potential contaminants of SST?

A
  • Sulfathiazole
  • Sulfanilamide
  • Succinic Acid
47
Q

What are 4 experimental factors that should be considered when attempting to isolate polymorphic forms of a solid pure substance?

A

I) Temperature
II) Pressure
III) Absolute Humidity
IV) Type of Solvent

48
Q

Define Steam Distillation

A

Process of co-distilling a compound with water

49
Q

Steam Distillation takes advantage of the…

A

Insolubility of most oil-like organic compounds in water

50
Q

Steam Distillation provides a route for separating…

A

Lower boiling (insoluble) compounds from higher boiling organic compounds or physical/plant matter

51
Q

Steam Distillation of an immiscible liquid mixture results in…

A

Each component of the immiscible mixture contributes to the total vapor pressure as if the other were not present

52
Q

Total vapor pressure = …

A

Sum of the vapor pressure of water + vapor pressures of each of the organic components in the mixture

53
Q

Define Dalton’s Law of Partial Pressures

A

States that the total vapor pressure of the mixture is always GREATER than the individual vapor pressures of the liquids in the mixture.

54
Q

Boiling point of a liquid is ___________ proportional to the vapor pressure.

A

Inversely

55
Q

The boiling point of a mixture of immiscible liquids must be ___________ than that of the lowest boiling component.

A

Lower

56
Q

A liquid or liquid mixture boils when the total vapor pressure of the liquid is equal to…

A

Atmospheric pressure

57
Q

The presence of any immiscible organic material contributes to the total vapor pressure in what way?

A

Causes the boiling point of water to drop below 100 degrees Celsius

Organic Chemistry Lab (Serena) (7 decks)

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