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getting an A on the Ochem lab final

Terms in this set (48)

(exp 1) what are the 4 characteristics of a good solvent?
1. volatile
2. chemically inert
3. must be soluble at high temperatures
4. impurities must either be insoluble at high temperatures or soluble at room temperature
(exp 1) how do you induce crystallization?
- scratch inner walls w/ a stirring rod
- introduce seed crystal
(exp 1) if crystals don't form, what went wrong and how do you fix it?
too much solvent, so you need to boil it off
(exp 1) how do impurities affect the melting point of a compound?
impurities both broaden and depress a pure compound's melting point
(exp 1) what kind of melting point dod you conduct to verify the unknown?
50:50 melting point
(exp 1) what are the 5 basic steps of recrystallization?
i Can Drive Really COOLy Imo
1. choose the appropriate solvent
2. Dissolve impurities in the hot solvent
3. Remove impurities via high temp. gravity filtration
4. COOL it down to induce recrystallization
5. Isolate the pure compound via suction filtration
(exp 1) what specific technique was used to collect insoluble impurities from the solution?
-high temp. gravity filtration
(exp 1) why did you rinse a cold solvent after suction filtration?
-to remove any remaining impurities
(exp 2) what are the 2 types of distillation?
-simple
-fractional
(exp 2) what is the difference between separation of the filtrations?
the difference between boiling points of miscible liquids
(exp 2) why was aluminum foil added to the apparatus?
-it was added in the fractional distillation to prevent heat loss.
(exp 2) what is Dalton's Law, Raolut's Law, and the combined law?
Dalton's law= Pt= P1 + P2 + P3....
Raolut's law= PA= PaCa + PbBc
combined law= PT= PACa+ PbCb
(exp 2) what is the difference between simple and fractional distillation?
- Simple distillation is for significally difference boiling points (over 100C difference). Fractional distillation is for less that 100C boiling points. It also has a fractional column.
(exp 2) know the apparatus of simple and fractional distillation.
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(exp 2) what is a fractionating column and how do you measure it's efficiency?
A fractionating column is a glass tube with tightly packed steel wool or glass beads. Vapor condenses and reevaporates in it.
- Efficiency is measured by column length, density of packed materials, and the amount of theoretical plates it can form.
(exp 2) what is a theoretical plate and azeotrope?
A theoretical plate is each mini distillation.
Azeotrope is a mixture of two liquids that form a constant boiling liquid of distinct proportions.
(exp 3) what are the 2 main types of extraction?
-solid-liquid extraction
- liquid-liquid extraction (w/ two sub types: acid-base extraction and organic-solvent extraction)
(exp 3) what is extracted from what?
trimyristin was extracted from nutmeg (25%)
(exp 3) what is the purpose of reflux technique?
Reflux is used to heat mixtures for extended periods of time w/out solvent loss due to extracting compounds or carrying out reactions
(exp 3) what 2 solvents were used?
-acetone was used to wash off impurities
- methylene chloride was used as a primary solvent
(exp 3) what techniques were used?
-extraction
-reflux
(exp 4) what is the separation based off of?
separation was based off of stationary and mobile phases.
(exp 4) what is TLC used for?
it's used to identify individual components in a mixture
(exp 4) what's the effect of polarity
polar compounds have strong interactions with polar stationary phases, so they elute slower (appear lower on TLC plate)
(exp 4) what is Rf and how is it measured?
Rf is retention factor
Rf is distance traveled by substance/ distance traveled by solvent front
(exp 4) what were the plates visualized with?
UV lamp
(exp 4) what were the 4 ingredients?
-ibuprofen
-acetaminophen
-aspirin (acetylsalicylic acid)
-caffeine
(exp 4) remember: .5% acetic acid in ethyl acetate
----!!!!!!!!!
(exp 4) what solvent system is used to dissolve the common anagesics (powder) in preparation of TLC spotting?
1:! ratio of methylene chloride to ethanol
(exp 6) separation is based off of what?
it is based off of solubility of protonated and deprotonated acids and bases
(exp 6) what was the solvent and its characteristics?
methylene chloride
-dense (below aqueous), high boiling point
(exp 6) what are the characteristics of an extraction solvent?
-it must be immiscible w/ the original solution (different polarities/ different densities). It must be more volatile than the liquid component and non toxic.
remember: like dissolves like
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what happens to an amine in acidic conditions?
it is pronated to become ammonium salt.
(exp 6) what happens to caboxylic acid in basic conditions?
it is deprotonated to become carboxylate salt.
if a mixture of benozic acid, benzocaine and diphenylmethanol in dichloromethane was extracted with the 1M sodium hydroxide, the acidic component of the 3-compound mixture would be located in the __________
Upper aqueous layer
in lab, you obtain a 1:1 mixture of compound Y (MP = 58-59) and compound H (MP = 76-78C). What would most likely be the melting point (eutectic point) ?
54-56C (bc MP goes lower with impurities)
caffeine is an amine, in which aqueous solution would caffeine be most soluble?
.82M HBr
which of the following laboratory techniques would be most efficient way to separate two miscible liquids whose boiling points are 75C apart?
fractional distillation
in the distillation experiment, the purpose of a fractionating column was to _______
increase the number of mini-distillations that occur in the apparatus
which solvent would not be appropriate for extracting caffeine from an aqueous tea solution ?
IDK
why is a boiling hcip added to the distilling flask before performing a distillation?
to prevent the solution from bumping
which liquid would be most efficient separating from acetonitrile (BP= 81) from simple distillation?
DMSO = BP 189C
in the separation of a 3-component mixture experiment, benzocaine was precipitated out of the aqueous layer via the addition of what specific solution ????
6M NaOH (6M sodium hydroxide)
what is the full name of the compound used as the source of hydrogen in the transfer hydrogenation of olive oil experiment?
cyclohexene
what was the full name of the neutral component used in separation of a 3 component mixture experiment?
diphenymethanol
what is the full name of the specific reagent used to brominate trans-stilbene in the preparation of diphenylacetylene experiment?
PHPB pyridinium hydrobromide perbromide
in the TLC analysis of analgesics experiment, what specific solvent system was used as the eluent for the development of TLC plates?
.5% acetic acid in ethyl acetate
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