Final Exam Flashcards
(154 cards)
1
Q
Azerotrope
A
- a mixture of two substances that distill at a constant temperature and with a constant composition, even though separately the components have different Bps.
- occurs when intermolecular forces take place (i.e. H-bond)
2
Q
Boiling Point
A
- temperature at which the vapour pressure equals atmospheric pressure
- constant for a pure substance
3
Q
Condensation
A
liquid that results when a gas is cooled
4
Q
Distillate
A
condensed liquid obtained from a distillation
5
Q
Slurry
A
a suspension of fine, solid particles in a liquid
6
Q
Volatile
A
tending to evaporate under ordinary temperature and pressure conditions
7
Q
Distillation (process explain)
A
process which involves heating a substance until it vaporizes, condensing the vapours by cooling, and collecting the condensate in a separate vessel called a receiver
8
Q
What is distillation used for?
A
- separating a mixture when the components of the mixture have different boiling points
- purifying a liquid
9
Q
What conditions must apply to accomplish a distillation?
A
- at least one component in the mixture must be volatile
- the components must not form an azeotrope
- if two or more volatile liquids are going to be separated via distillation, they much have a wide separation in their boiling points (at least 50 degrees Celsius)
10
Q
What’s an example of an azeotrope?
A
water and ethanol
11
Q
Refractive Index
A
- measure of the change in the light path (refraction) as light passes at an angle from one medium to another (i.e. air to liquid)
- due to difference in light velocity in the two media
- extent to which the beam is refracted is dependent on on the relative concentration of atoms and on the arrangement within the molecule
- unique property to each medium
20
n =symbol for refractive index at 20 degrees Celsius
D and standardized to the sodium D line (WL=589
nm)
12
Q
Simple Distillation
A
as soon as liquid boils, the vapour is collected in the condenser without any change in its composition
(other notes)
- observed boiling points are always between the boiling points of the pure components, rising gradually as the distillation proceeds
- only an enrichment of either component at certain stages of the distillation, but a clear-cut separation is not attainable
13
Q
Fractional Distillation
A
- before the vapour is removed, it is re-equibilrated and the resulting vapours that are condensed with a higher composition of compound A
- the final distillate will be nearly pure
- fractioning column permits repeated exchange of molecules between the liquid and vapour phases
14
Q
Fractioning column
A
- permits repeated exchange of molecules between the liquid and vapour phases
- packed with round glass beads that provide large cooling surfaces for the multiple condensations and vaporizations that take place
15
Q
Where does the thermometer go in the still head adapter?
A
-inserted with the bulb just below the bottom of the sidearm on the adapter and the immersion ring on the thermometer is hidden by the rubber adapter
16
Q
Why is it important to place the thermometer in the proper location in the still head adapter? What happens if it’s too high? Too low?
A
- the thermometer will give an inaccurate reading of the temperature
- too high= the thermometer will not be adequately bathed in the vapour path and the boiling temperature will be too LOW
- too low= the thermometer would come in contact with the superheated vapours and register a boiling point that is too HIGH
17
Q
What is a rheostat?
A
regulates the heating mantle (thing on the wall with temperature gauge)
18
Q
When is a boiling chip added to a solution? When is it necessary to add another one?
A
- before the substance is heated
- after a substance has cooled, another boiling chip must be added
19
Q
How can large heat losses be minimized during a distillation?
A
-by insulating the distilling flask and still head adapter (and the fractioning column) with aluminum foil shiny side in
20
Q
What is extraction used for and what differences is it based on?
A
- separating mixtures (liquids or solids)
- based on the differences in solubility of the components in two immiscible solvents
21
Q
What characteristics must the two solvents selected for an extraction have?
A
- first solvent= completely dissolve both compounds
- second solvent=immiscible with first solvent and dissolves only one compound and dissolve it better than the first one
22
Q
partition coefficient of extraction
A
-the extent of the solute to dissolve in the first solvent despite being more soluble in the second solvent
23
Q
Why is successive extraction necessary?
A
- because some of the solute will still be dissolved in the first solvent despite being more soluble in the second solvent
- to ensure that the “best” possible separation of the components in the mixture is done
24
Q
Solutions should never occupy more than how much of the volume of the separator funnel? Why?
A
2/3 (two thirds)
-proper mixing
25
Why is it not necessary to use a dry separatory funnel?
-an aqueous layer will always be put inside it (in Chem 235 at least)
26
emulsion
- finely dispersed suspension of one liquid layer in another which happens when dissolved materials in these liquids cause the mutual solubility of the two layers to increase
- "foamy" layer between two immiscible layers
- separation is not possible when an emulsion is present
27
How do you get rid of an emulsion?
- wait 10-20 minutes
- gently swirl flask
- if water is one of the solvents, saturated NaCl can be added to pull it out of the water (NaCl is MUCH less soluble in organic solvents than water)
28
Why is a drying agent necessary for the organic layer after an extraction?
-the organic layer is usually saturated with water and it must be removed before the organic solvent is evaporated away to leave behind the solid
29
Drying agent
- inorganic salt that can form hydrates
| - absorb excess wate
30
Commonly used drying agents
- Magnesium sulfate
- Sodium sulfate
- Calcium chloride (for hydrocarbons or alkyl halides)
31
How do you know when enough drying agent has been added?
- when the drying agent swirls freely and it does not clump at the bottom of the flask
- about 1/10th of the liquid's volume should be added
32
Why must all glassware be dry after filtration of the solution and drying agent?
-all water has been REMOVED from the solution and you do not want to reintroduce it to the system
33
What are the steps for using a rotovap?
-make sure RB is less than half full
-place RB flask on end and clip in with the blue clamp
-rotate stopcock to ON position
-turn SPIN dial on to maximum
-lower RB flask into hot water
-watch until dripping slows
-reverse order to shut down/take RB flask off rotovap
(raise RB, stop spinning, turn off, unclip)
34
Anhydrous
- "without water"
| - all water has been removed (will absorb water readily when it comes in contact with it)
35
Percentage recovery
- final weight of a substance divided by the original weight of the same substance multiplied by 100
- used during recrystallization to determine how much was lost
36
Successive Extractions
- taking the total volume of extracting medium and splitting it into several positions and adding each portion to a separatory funnel containing immiscible solvent, mixing and removing this portion of the extracting medium before adding the next portion
- ensures "best" possible separation of components in a mixture
37
Boiling chip
- granules of porous alundum which release bubbles of entrapped air to a solution as it is heated
- allow vapour of a boiling liquid to be smoothly led to the surface and released
38
Bumping
- the sudden violent surge of vapour breaking from the surface of a liquid
- liquid becomes superheated if there are no air pockets and the liquid rises above the boiling point
- prevented by boiling chips and stirring
39
Condenser
- apparatus in which gases are cooled into a liquid state
| - the direction of water flow is always against gravity
40
Ice bath
-a mixture of water and ice, with more water
41
Refluxing
-process whereby a heated liquid evaporates, enters a condenser, cools back to a liquid, and flows back into the original boiling solution
42
Saturated (solution)
-maximum amount of solute has been dissolved
43
Scratching
-using a roughened end of a glass rod to pull a little of the recrystallization solvent above the surface of the liquid while "scratching" the rod against the side of the container to give a rough area for the first crystal to form
44
Seeding
-placing a "seed," or pure crystal, of a substance into a saturated solution to start the growth of the crystal lattice
45
What's the advantage of using a condenser?
- helps to maintain a constant volume of the solvent, which would evaporate away while being boiled
- the compound could evaporate away with the solvent as well in a saturated solution
46
How do you calculate percent recovery?
amount of substance collected/amount of substance supposed to be collected *100
pure/impure *100
47
When do you hot filter a solution?
- when there are insoluble impurities in the solution
| - when there are coloured, soluble impurities (Norit and Celite are needed)
48
When and how do you use Norit?
- when there are coloured, soluble impurities in a solution
- the coloured substances attach to the activated surfaces of the Norit by adsorption and can be filtered off
- solution must be cooled before Norit is added
- filtered off by hot filtration
49
What is the purpose of using Celite with Norit?
-tiny Norit particles are absorbed onto Celite surfaces and it prevents Norit (tiny charcoal particles) from going through the filter paper and into the filtrate below
50
mother liquor
-the solution that remains after a crystallization
51
melting point
temperature at which the crystalline solid and the corresponding liquid phase are at equilibrium, under an external pressure of 1 atmosphere
52
melting point range
temperature when the first drop of liquid appears amongst the crystals of the compound to the temperature at which completer liquefaction takes place
53
What is a criterion of purity for the organic compounds that exist as solids at room temperature?
-a sharp melting point, unchanged by recrystallization
54
What will happen to the observed melting temperature when a temperature is going up too fast in a melting point test?
-the observed m.p. will probably be lower than the true m.p., since at this rapid rate of heating, there is a "lag" between the thermometer reading and the actual temperature of the heating block
55
What should you do if you notice that your substance is subliming? (shrinking and forming a fog--- goes directly from solid to gas)
add more sample on when taking the melting point
56
Mixed melting point
-melting point of an intimate mixture of two crystalline samples
57
absorption
-the drawing up of a liquid through a mass, permeating the bulk of the absorbing material
58
Adsorption
- a special kind of absorption restricted to the adhesion of material to the surface of the bodies, attached either by chemical or van der Waals forces
- adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent
59
Rf
-distance travelled by a solute on a TLC plate divided by the distance travelled by the solvent on the same plate
(spot travelled to)/(total distance)
60
Streaking (tailing)
- "streaking" of a substance along a TLC plate
- usually occurs if too much of the initial material is spotted on the plate or material is very polar and more attracted to the plate
61
What is a solvent pair?
- two or more miscible solvents that form a mixture when added together that have the appropriate properties for recrystallization
- one dissolves very well and one dissolves poorly
62
Schlierien lines
- streaks or wavy lines in a solution indicating regions of different densities
- indicates partial dissolving
63
Yield
-weight of the substance that has been produced
64
Soluble in Diethyl Ether
-most organic compounds
65
Soluble in Water
-low MW organic compounds and salts
66
Definition of alkaline
Basic, pH > 7
67
aqueous phase
the liquid layer in which water is the solvent
68
How do you perform a benchtop extraction?
1) Scrap up the solid and purify by recrystallization
or
2) soak up solid or liquid with cotton that has been saturated with a suitable solvent and then extract the substance from the cotton with more solvent
69
catalysis
the acceleration or promotion of a chemical reaction by a reagent (i.e. catalyst) which itself remains unchanged
70
Corrosive
having the ability to cause immediate damage upon contact
71
hygroscopic
attracts moisture, i.e. absorbs moisture from the air
72
Limiting reagent
reagent which is present in the lowest amount, according to the stoichiometric relationship of the reaction
73
mole percent
```
#moles of the substance in question/
#moles of all substances in mixture
```
74
What is norit?
activated Charcoal that can be used to absorb small amounts of colored, soluble impurities from a solution
75
organic phase
the liquid layer in which an organic liquid is the solvent
76
percentage yield
actual yield (mass) of substance / theoretical yield
77
quantitative transfer
* transfer of a substance from one container to another so that none of the substance is left behind in the original container
* accomplished by rinsing original container with suitable solvent several times
78
solubility
amount of solute that will dissolve in a set volume of solvent **at a given temperature
79
TLC
* "thin layer chromatography" used to analyze a mixture by separating out its constituents by means of selective adsorption
* partitioning process based on differences in polarity
80
turbidity
"cloudiness" in a solution (usually caused by immiscible compounds
81
What is the main difference between a distillation and refluxing?
* During a distillation the condensate is collected in a separate container called the receiver
* During a reflux the distillate is goes back into the original vessel
82
What will happen to the measured boiling point when distilling a pure substance?
It will remain constant throughout the distillation
83
What happens to the measured boiling point during a distillation? Why does this occur?
* The BP will vary continuously during the distillation
* the composition of the liquid being distilled will vary during the distillation as one of the compound distills and falls into the receiver
* vapour pressure of the liquid varies with its composition thus will the bp
84
What is a tieline? what is it used for?
* A straight horizontal line that connects the liquid (composition vs temp) graph to the vapor (composition vs temp) graph for the results of a distillation
* determines the vapor that is in equilibrium with the boiling liquid at any given point in the distillation
85
As the distillation proceeds, the composition of the liquid ____________ and the boiling point _______________
shifts to the right, increases
86
What is the criteria of purity for a liquid?
* boiling point of the neat liquid
| * refractive index (R.I) of the liquid
87
Why can a refractive index be used to determine the concentration of solutions?
The refraction of light is an additive property (i.e. dependent on the # and kinds of atoms in the molecule)
88
What do you attach to the end of the condenser to help collect the distillate during a distillation? How do you secure it?
takeoff adapter secured with an elastic band
89
Should we ever add a boiling chip to a hot solution? Why?
No, violent frothing may occur
90
What is an appropriate dropping rate of the condensate?
one drop per second
91
What does the thermometer measure during a distillation? How does it do this?
* Measures the equilibrium of the vapor and liquid temperature
* droplet of condensate on thermometer + vapor around (should always be a droplet here!)
92
When do we use an air-cooled condenser during a distillation? Why?
When distilling very high boiling points because glass cracking may occur if the hot vapors come into contact with the cold condenser
93
How do you prevent evaporation of the distillate?
Cool the receiver in an ice bath
94
How do you calibrate a thermometer? When is this required?
Submerge thermometer, below the immersion line, in a slurry of crushed ice and water
* check the temperature after a few minutes, if it doesn't read zero adjust ALL measurements
* Calibrate when using a thermometer you've never used/calibrated before
95
How do you prevent dripping once you've stopped a distillation?
Turn the takeoff adapter up
96
extracting medium
(second) solvent that pulls out one of the components dissolved in the other (first) solvent
97
What is the total final volume in a distillation?
Volume distilled + volume of residue
98
What is the proper order for the stopcock on a separatory funnel? Does is require stopcock grease?
(inside) white washer, black O ring and lock nut (outside)
99
How do you remove the top layer of a separatory funnel?
Drain the bottom layer through the stopcock, then decant (i.e. pour) the top layer out of the top
100
What methods are there for removing an organic solvent from a desired compound?
* evaporation on a steam or hot water bath (under fumehood)
* evaporation at reduced pressure
* distillation (if solute is high boiling liquid/solid)
* evaporation with rotary evaporator
101
Why did aqueous hydrogen chloride allow for the separation of a weakly basic compound from a neutral one during extraction?
* The weak base reacted with an acid and became an ionic salt while neutral compound was unaffected
* ionic compounds more soluble in water (i.e. aqueous layer) than ether
102
How did we regenerate the weak base in our extraction and separate it from the aqueous layer?
* Add base to deprotonate ionic salt
| * Wash with ether (base is more soluble in it) to extract from aqueous
103
Which layer ends up on top in an extraction?
the one with least density
104
How do you do a litmus test on a solution in a beaker?
Use the glass stir rod to stir the solution, pull the rod out of the beaker from the centre and place a drop of solution on a piece of litmus paper
105
Why must all water be gone before using the rotovap?
The rotovap only works for solvents that would normally boil at temperatures less than 60C at atmospheric pressure
106
Why do we spin the RB flask in a rotovap?
Creates more surface area of the liquid being distilled, thus increases rate of evaporation
107
What is the purpose of the vacuum in a rotovap?
Creates reduced pressure, liquid can now boil (thus evaporate) at a lower temperature
108
How does recrystallization purify a solid?
* soluble impurities are often in small concentrations thus remain in solution under both hot and cold conditions
* growing crystals reject the impurities because they do not meet the geometry of the crystal lattice
* insoluble impurities are usually removed while the solution is hot bu hot filtration
109
What makes for a good recrystallization solvent?
* Dissolves compounds sparingly or not at all at room temperature
* Dissolves compound readily at boiling point
* Dissolves compound in a reasonable volume
* Does not react with the compound
* Either dissolved impurities very well or not at all (so they can be removed by hot filtration)
* boiling point is below compounds melting point
110
What is oiling out?
During recrystallization when the compound (solid) melts but does not dissolve, due to solvent BP being higher than solid's MP
111
How do you choose a solvent pair?
One solvent dissolves readily at room temp, other does not dissolve at any temperature
112
Why do we turn the flask to 45degrees when growing crystals?
To allow greater depth for proper crystal growth and the expulsion of impurities
113
Why do we do recrystallizations in an Erlenemeyer flask and not a beaker?
* narrow neck allows refluxing thus minimizes surface evaporation
* can be corked to allow vapor and liquid to equilibrate
* maintains amount of solvent
* can be swirled and easy to remove crystals
114
Why is swirling important in a recrystallization?
Facilitates dissolving of the solid and prevents bumping
115
What must you do before performing a hot filtration? Why?
Additional solvent about 1/4th the original volume then bring again to boil, prevents premature precipitation of the solid
116
What temperature do you want to preheat your glassware to for hot filtration? Why?
Temperature just below the boiling point of the solvent, prevents premature precipitation of the solid
117
Why is Norit a good tool for removing impurities?
It is not soluble in any solvent
118
Why must a solution be cooled before adding Norit?
it causes uncontrollable frothing in a boiling solution
119
What methods can you use to stimulate crystal growth?
scratching, seeding, evaporating off solvent or adding incompatible solvent
120
In what order do we stop suction during vacuum filtration? Why?
Detach the tubing from the water pump, then turn off the pump to prevent back suction
121
How do impurities affect melting points?
Lowers melting points and widens the range
122
How would you determine if two compounds, with the same melting point, are identical with a melting point measurement?
If you mix the two and the MP is unchanged they are identical
123
At what rate should the temperature increase when taking a MP?
2C per minute
124
What kind of compounds CANNOT be used in TLC?
Volatile compounds
125
How does TLC work?
*small amount of compound is dissolved in volatile solvent, which then evaporates leaving the compound adsorbed onto the plate
* Compound spotted on plate is attracted to the moving liquid phase
* Compounds move different heights depending on structure (less polar travels further)
126
Name the purposes of TLC?
* Determine # compounds present
* Determine if two compounds are identical
* Determine appropriate solvent for column chromatographic separation
* Monitor a column chromatographic separation
* Check effectiveness of column separation, recrystallization or extraction
* Monitor progress of rxn
127
What is the purpose of the half-moon shaped filter paper during TLC?
* Used as a liner in the developing chamber
* saturate the chamber with vapors
* reduce evaporation of the developing solvent from the TLC plate
* maintain rate of irrigation process
128
What do we do when doing a TLC analysis on a very polar compound? Why?
Add a few drops of acetic acid to increase the polarity of the developing solvent (thus decrease the attraction between compound and polar stationary phase)
129
What are TLC plates made out of?
Coated with silica gel and pretreated with a fluorescent dye
130
What compounds cannot be detected with an iodine chamber in TLC analysis?
saturated hydrocarbons and halides
131
What information needs to be on an official label?
* Name, lab section, locker #
* Date sample prepared
* Name and structure of sample
* Yield and %yield
* Any physical constants measured
132
What are the indication of partial solubility / complete solubility?
* Soluble: solid disappears
| * Partial solubility: schlierien lines, gas formation or color appearance BUT solid does not disappear
133
Esters are made by reacting ______________ with __________ . This rxn is _____________ and its rate is ___________.
carboxylic acid, alcohol, reversible, determined by the steric hindrance of the two reactants
134
How do you produce amyl acetate?
Esterfication of acetic acid and amyl alcohol catalyzed by sulfuric acid
135
What does a water wash do in an extraction?
Allows aqueous and organic layer to separate
136
What does a NaHCO3 wash do in an extraction?
Reacts with acids in organic layer to form an ionic salt which is then pulled into the aqueous layer
137
What does a NaCl wash do in an extraction? How does it do this?
* Removes excess water
* NaCl breaks up the emulsion (formed by slight mutual solubility caused by the presence of compounds) formed between water and organic layer
138
Why did we distill our organic layer after extraction (exp 7)?
To separate out ester from the ether layer
139
In exp 7, what was left in the flask once the reaction went to completion? Why?
Acetic acid (because it was used in excess), sulfuric acid (because it was a catalyst) and water (because it is formed in the process)
140
Define Grignard reaction
* synthesis reaction involving an organometallic halide
| * reacts with acidic hydrogens to make hydrocarbons and metal salts
141
What characteristics does a Grignard reagent have?
* Strong base, good nucleophile
| * Reacts quickly with acidic hydrogens
142
Why must the Grignard reaction be done under anhydrous conditions?
It will readily react with water
| R-MgX + H-OH = RH + HOMgX
143
How do you prepare a drying tube?
In spherical section of the drying tube add:
| *(bottom) cotton wool, CaCl2, cotton wool (top
144
What do we do in the Grignard reaction after adding the Mg turnings to the RB flask but before adding the other reactants?
Hold the flask at 45degrees over a bunsen burner and flame the flask (rotating) until all surface evaporate it gone
145
How do we control the drip rate in the Grignard reaction?
Use a hot water bath and ice bath to fluctuate the temperature as necessary to achieve a drip rate of 1 drip per second
146
How do you know a Grignard reaction has started?
* color disappears then reappears
* bubbles coming from Mg not solvent
* appearance of white precipitate
* heat from bottom of flask
147
Is a Grignard reaction exothermic or endothermic?
Exothermic
148
How long should you allow a Grignard reaction to reflux?
20 mins
149
What did we do to our reacted Grignard rxn mixture after it finished refluxing? Why?
We poured it into a beaker of ice and sulfuric acid to react any excess Mg solid and ice because its an exothermic reaction
150
What are the steps to using the Abbe Refractometer?
* Turn power switch down to on position
* Open prism to the left and clean with acetone moistened tissue
* Put 2-3 drops of sample on the bottom prism using a clean pipette (don't touch w/pipette)
* Close prism, lift light against prism
* Look into eye piece
* Turn coarse adjust until light/dark line is at the crosshairs
* Turn fine adjust until a sharp line between dark and light appears
* Hold power switch down to view scale, record temp on thermometer
* clean prism with tissue moistened w/acetone
151
What does the coarse adjust knob do?
On refractometer is adjusts the position of the interface to the crosshairs
152
What does the fine adjust knob do?
On refractometer is sharpens the interface
153
How is a refluxing set up different for a flammable vs non-flammable solvent?
* Flammable solvent uses hot water bath and ice bath to control the temperature
* Non-flammable uses a thermowell connected to a rheostat to control the temperature
154
What do we do when we finishing fluting filter paper, before using it? Why?
Invert it, so any grease from your hands remains on the inside and will be disposed of
