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Z - Chem 2219 (S&T) > Final, Other Information > Flashcards

Final, Other Information Flashcards

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1
Q

Using a phase composition diagram, how do you find boiling point from a mole fraction?

A

the intersection of the bottom liquid curve with the mole fraction

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2
Q

Using a phase composition diagram, how do you find the still head temperature and final mole fraction from an initial mole fraction?

A

from the intersection of the bottom liquid curve with the mole fraction, go left until you reach the other curve, then down to the lower curve

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3
Q

Using a phase composition diagram, how do you find the composition of the distillate (final product) from a still head temperature?

A

find the intersection of the still head temperature with the liquid curve

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4
Q

Using a phase composition diagram, how do you find the number of theoretical plates from an initial and final mole fraction?

A

(start and end on the lower liquid curve) go left until you reach the top curve, then down until you reach the bottom curve and repeat

each horizontal line you create is one theoretical plate

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5
Q

In a phase composition diagram, which curve is which? Which curve are temperatures measured off of? What is the significance of a still head?

A

The top curve is the vapor, and the lower curve is the liquid.
Temperatures are always measured in the liquid curve.
Still head is when the vapor turns back into a liquid

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6
Q

What are the two types of GC columns?

A

Capillary and Packed

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7
Q

Describe the structure and size of the smaller of the two types of GC columns.

A

Capillary
made of fused silica capillary tube coated in the interior wall with polymer
give better separations, use less sample, and can separate complex mixtures containing many compounds, but they require more sensitive detectors.
~.3mm (.1-.5mm)

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8
Q

Describe the structure and size of the larger of the two types of GC columns

A

Packed
made of tubing packed with small, uniform size, inert support coated with a thin film of nonvolatile liquid
~3mm (1/8in-1/4in) (3mm-6mm)

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9
Q

What are the two types of GC detectors? Describe them. Which can detect water?

A 
What are the two types of GC detectors?
TC (thermal conductivity)
works with a packed column
the column gas flow cools a heated filament and the change in temperature causes a change in electrical resistance. The difference between that and the reference (only the gas) is used
Can detect water
FID (flame ionization detector)
works with a capillary column
 the sample is burned in a H2 flame creating ions that cause the flame to conduct current, resulting in a signal
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10
Q

Give the column type, detector type, and amount of sample used per analysis for our GC.

A

Our lab uses capillary columns and a FID. It requires about .1-.2 ul per analysis.

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11
Q

Describe the effect of GC column temperature on separation and resolution.

A

The separation of peaks is determined by the column temperature: as it increases, the peaks elute more rapidly and separation decreases.

Low Temperatures=compounds with lower BPs spend more time in the mobile phase than those with higher BPs. The lower boiling compounds move faster and come off the column sooner.

High Temperatures=all compounds spend more time in the mobile phase, causing all compounds to move faster

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12
Q

How do you determine theoretical yields?

A

use an H bar converter to move from grams reactant-> mole-> mole product -> grams product

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13
Q

What is the equation for percent yield?

A

(measured)/(expected) * 100

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14
Q

What is the equation for percent error?

A

(Expected-Measured)/(Expected) * 100

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15
Q

What is the effect of a dissolved nonvolatile solid on the BP and FP of a solution?

A

Dissolved nonvolatile solid will always raise the BP of a solution
Dissolve nonvolatile solid will always decrease the FP of a solution

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16
Q

What is the effect of soluble or insoluble impurities on MP results?

A

Soluble impurities lower MP and widen the MP range for a compound

Insoluble impurities should have no effect on MP

Melting Point is a range between the first visible melting and the final disappearance of all crystals

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17
Q

How do you run a mixture melting point to determine the identity of a compound?

A

1: Run MP of compound
2: Rerun MP of compound mixed with known pure sample thought to be the same compound

(can keep doing MP with
gradually increasing mixtures of sample and known compound)

If the MP of mixture remains the same, the compounds are the same
If the MP of mixture is lower and wider, the compounds are not the same

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18
Q

Describe eutectics. What would a graph of one look like?

A

Eutectic points are where the composition of a mixture of two solids have a MP lower than either pure substance or any other mixture of the two.

Y-Axis MP and X-Axis Composition

U/V ish curve that reaches its lowest point somewhere in the middle of the graph

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19
Q

Describe azeotropes. What would a graph of one look like?

A

An azeotrope is a non-ideal binary liquid mixture. Low boiling azeotropes are more common. At the minimum or maximum BP azeotropic composition, the liquid and vapor have the same composition and cannot be separated by distillation. Changing the distillation pressure can move or eliminate the azeotrope.

Y-Axis BP and X-Axis Compoisiton

Two ovals that join their two corners somewhere in the graph, usually in a lower area

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20
Q

How do you calculate retention factor when doing TLC plates?

A

(distance from starting line to center of sample spot)/(distance from starting line to final solvent front)

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21
Q

How do you calculate theoretical plates when doing TLC plates?

A

N=16(distance from starting line to center of sample spot/diameter of spot)^2

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22
Q

What is the relationship between compound polarity and Rf?

A

Lower the polarity the higher the Rf. The stronger a compound is bound to the adsorbent, the slower it moves up the TLC plate.

23
Q

What is the relationship between solvent/eluent polarity and Rf?

A

In general, the more polar the eluent, the more rapidly a given compound moves, and the higher the Rf. Polar compounds, which are strongly attracted to the absorbent, require polar eluents to attract them away from the adsorbent. Solvent polarity should be arranged so that it spreads compounds across plate.

24
Q

What would a TLC plate look like if the solvent was not polar enough, just right, or too polar?

A

Clumped together at the bottom, spread out in the middle, clumped together at the top

25
Q

What problems would this TLC error produce?

tanks not dry and/or saturated with solvent vapors

A

irreproducible Rf values

26
Q

What problems would this TLC error produce?

solvent above the starting line

A

samples leached from plate-> no spots after development

27
Q

What problems would this TLC error produce?

solvent reaches top of plate

A

bad Rf values

28
Q

What problems would this TLC error produce?

sample too concentrated

A

tailing spots

29
Q

What problems would this TLC error produce?

too much sample volume

A

large, poorly resolved spots

30
Q

What problems would this TLC error produce?

spots (starting line) placed too close to edge of plate

A

distorted spots

31
Q

Arrange these compounds in order of polarity, in decreasing order.

Acetone, CH2Cl2, Ethyl Acetate, Hexane, Toluene, Water

A

Water-> Acetone-> Ethyl Acetate-> CH2Cl2 -> Toluene -> Hexane

32
Q

In the column chromatography experiment, what dyes did we elute and what compounds did we use to elute them?

A

We used dyes of fluorescein and methylene blue. Methylene blue was eluted with ethanol, then water was used to elute fluorescein

33
Q

In the column chromatography experiment, how do you measure theoretical plates?

A

The number of theoretical plates were found using the equation N=16(tR/wB)2.

TR is retention time, measured by the distance between the top of the column and the center of the dye

WB is baseline width, measured by the height of the dye band

*Both are measured when the band is near the bottom

34
Q

What are the four solvent selection criteria for recrystallization?

A

The compound being purified must be insoluble in the solvent at RT.
The compound should be soluble in boiling solvent.
The solvent BP must be lower than the compound MP.
Abundant crystals should be recoverable from cool solvent.

35
Q

Describe the major problem that can occur in recrystallization and how to avoid it.

A

Oiling Out: When a compound forms a molten oil rather than crystals

Fixable with seed crystal or proper solvent selection

(may also happen when heating too fast)

36
Q

Define vicinal dihalide

A

Halogens are attached to adjacent carbons

37
Q

Define diastereomers

A

Stereoisomers that are not mirror images of each other

38
Q

Define enantiomer

A

Chiral compounds which are non-superimposable mirror images of each other

39
Q

Define racemic mixture

A

A 50/50 mixture of enantiomers

40
Q

Define meso compound

A

A compound containing chiral centers but also containing an internal plane of symmetry, making it optically inactive

41
Q

Define optically active

A

A chiral compound which rotates the plane of polarized light

42
Q

Describe R/S notation

A

Refer to absolute configuration of groups about a chiral center, going from largest to smallest with H placed away from the observer.

43
Q

Describe Fisher Projections

A

compound is depicted as a grid of lines, those pointing up are back, those pointing to the sides are forward

44
Q

How do you determine the possible products from the dehydration of a branched alcohol?

A

put a positive charge where the OH used to be, then form a resonance structure

the double bond can be formed in either direction, giving you four products (with possible repeats)

45
Q

What does a chemical test of 2% Br2 in CH2Cl2 test for? What does a positive test look like?

A

Alkene double bonds

Loss of bromine color (dark, red-brown)

46
Q

What does a chemical test of 1% KMnO4 in H2O (+ DME) test for? What does a positive test look like?

A

Alkene double bonds

Loss of permanganate color (purple), turns brown

47
Q

What does a chemical test of Ce(NH4)2(NO3)6 (+ DME) test for? What does a positive test look like?

A

Alcohols

Formation of a colored complex

48
Q

Define salting out in relation to extractions

A

K=Partition Coefficient: The ratio of the solubility of a compound in the organic layer to its solubility in the water layer

Salting Out: K can be increased by adding inorganic salts to the aqueous phase. This reduces the solubility of the organic compound in the aqueous phase, driving it into the organic solvent phase, improving extraction efficiency.

49
Q

Define a wash in relation to extractions

A

Pulling unwanted impurities away from the desired compound

50
Q

Describe the use of acid/base reactions in extractions

A

in our extraction, reacting some of our compounds with bases turned them into ions, which were then pulled into the aqueous layer

51
Q

What is the general mechanism for a Diels-Alder reaction?

A

Electrons from double bond on dienophile connect to one of the double bonds of the diene, which pushes that double bond over and makes the electrons from the other double bond connect to the dienophile

52
Q

What is the stereochemistry of a Diels-Alder reaction?

A

Stereospecific: Syn Addition with retained configuration of the dienophile
May produce enantiomers
Diene only reacts in the c-cis conformation, if it is in the c-trans it will either change to c-cis or not react
Occurs primarily in an endo fashion (substituents are pointing inside of the largest ring)

53
Q

What is an emulsion? How might you get rid of one?

A

Suspensions of droplets of one immiscible liquid in another. These are more likely to form in the mixture is shaken excessively. They can be broken with the addition of NaCl solution, stirring with a glass rod, allowing to sit, or centrifuging.

Z - Chem 2219 (S&T) (13 decks)

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