CHEM 237 Final - TAMU - Everything

overall, what is Recrystallization?

-a common lab method to purify solids by dissolving them in hot solvent, filtering while hot, then allowing the filtrate to cool so that crystals form -[the process of dissolving a solid material into a suitable solvent or mixture of solvents and allowing the material to crystallize from this solution]

For the chemically active solvent extraction of a three‑component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolved in dichloromethane: what is the procedure to... dissolve the emulsion due to benzocaine salt exceeding its solubility?

-add water to the sep funnel that conatins an acidified 3-component mix in DCM

For the chemically active solvent extraction of a three‑component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolved in dichloromethane: what is the procedure to... handle the sep funnel properly?

-cradle the sep funnel in the palm of your hand AND hold the stopper between the fingers of the same hand

The experiment states that a distillation should never be continued until distilling flask is dry. Does that mean 'no water present' as when using a drying agent on an organic solution? Explain.

-it means that there would be nothing in the flask at all whether that be water or something else

for recrystallization: what are the requirements of the solvent? (3 rqrmnts)

-it should NOT chemically react with the compound -it should dissolve the compound white HOT [never cold for dissolving] - it should either dissolve the impurities at ALL temperatures or NOT at all

what is the first step in using a sep funnel for extraction?

-make sure the funnel stopcock is closed -then carefully pour the liquid to be extracted into the funnel

what are 3 reasons hypochlorous acid is used more often as an oxidizing agent, rather than dichromate?

-safer -less expensive -environmentally friendly

what influences solubility in water for organic molecule?

-the amount of hydrogen bonding occuring, which counteracts the organic hydrocarbon affinity of the rest of the carbon

Why can AZEOTROPES NOT be separated by simple distilation?

-the vapor has the sae poroprtions as the unboiled mixture. -as a result, an unkown liquid that boils at a constant temperature is NOT necessarily pure and can potentially be classified as an azeotrope

what experimental observation on the initial dissolution of compound with hot solvent would let you know that hot filtration was not needed?

-there would be no visible solid impurities after you have added the solvent -[others]

when using a sep funnel: what should students do with the first layer and acid washes?

-they should wait until they are absolutely certain that they have all the layers needed before throwing ANYTHING away -they should NEVER throw a layer away

when would a hot water vacuum NOT be necessary or useful in a purification by recrystallization?

-when the impurities dissolve into the solution at high temperatures also or -when NOTHING dissolves [you would be removing impurities and the cmpd you want to recrystallize] or -when the needed compound already dissolves at room temperature; no need to heat it up to remove impurities

Finish the statements for MP determination: pure substances typically have a melting RANGE of ...

... less than 2 C [between the upper and lower limit]

Finish the statements for MP determination: the literature value of the melting point range is often quoted as...

... only the upper limit of the range

Finish the statements for MP determination: the upper limit of the melting point range occurs when...

.... the last crystal melts

Finish the statements about Rf values: the distance the spot moves is measured from...

...from where the spot starts to the CENTER of where it ends up

Finish the statements about Rf values: the distance the solvent has moved is measured from..

...from where the spots start [origin] to where the FRONT of the solvent ends up

Finish the statements for MP determination: the lower limit of the melting point range is when ...

...the first crystals start to melt

Finish the statements for MP determination: the melting point is a physical measures of the (...)

...the forces holding the material into its crystal lattice

what are the min and max values for Rf?

0 and 1 [its just a ratio]

The IR spectrum displays the wavelengths at which specific functional groups absorb energy. Which wavelength do each of these bonds absorb energy? 1. C--C [Alkene] 2. N-H [amine] 3. C--O [ketone]

1. C--C: 1600 cm-1 2. N-H: 4000-3000 cm-1 3. C--O: 1800-1640 cm-1

Label each of the statements as true or false: 1. infrared spectra can detect impurities in a sample 2. infrared spectroscopy is nondestructive 3. IR is good for detecting and identifying functional groups in a sample 4. IR can be used to detect most any kind of sample

1. T 2. T 3. T 4. F IR is not good at detecting all mixtures

a preliminary investigation reveals that an unknown material has a melting point range around 150 Celsius. [http://dam.saplinglearning.com/authkey/onB_C4P/preview/F6xfN72X4WcAPT3dq4zCOH/previews/maxWidth_1600_maxHeight_1600.jpg////ochem_graphB_1726114_preview.jpg?_=2] what voltage mus the melting point apparatues be run at to produce a 2 C/min change near 150 C?

45

The following statement describes possible compounds that might have be steam distilled with eugenol in the preparation clove oil, but then would remain in the organic phase when extracted with base. Identify the statement as true or false and explain answer: "they might contain CO2H groups"

FALSE These would be polar and not be in the organic layer

why would HCl be a poor choice as an acid catalyst for the formation of cyclohexene be dehydration of cyclohexanol?

HCl has a strong nucleophile [Cl-], so when it is added to the alkane, it may form a substitution product rather than just dehydrating the cyclohexanol

in the positive triiodide-starch paper test, were the iodide anions in the test paper oxidized or reduced? [what type of reagent (oxid or reducing) causes a positive test?] what cause the color observed in the test paper?

The iodide anions were oxidized. The iodine anions were ozidized by oxidizing agents, including HOCl. A complex of I2 and I- absorb into the starch and creates the strong blue-black color.

the suggested procedure for spotting a sample on a TLC plate involves transferring a droplet of concentrated solution from a capillary onto the plate, allowing it to dry, then repeating the process over the existing spot. Why is it advised to spot multiple times

To facilitate visualization by having a higher compound concentration

1-chloro-1-phenylethane undergoes solvolysis in water by an SN1 mechanism to make 1-phenylethanol. The reaction is followed with bromothymol blue indicator and an aliquot of NaOH base. What is the slowest [rate-determining] step?

the first is the slowest bc a bond is being broken

(The gauche conformation of butane occurs when the dihedral angle between at the C1-C2 and C3-C4 is 60 degrees. There is sterric strain in the molecule due the proximity of the two methyl groups.) Would the magnitude of this sterric strain increase OR decrease if the dihedral angle was increased from 60 to 65 degrees? Why?

the magnitude of the sterric strain will decrease because the groups are moving farther apart

why is a pencil used for TLC instead of using a pen?

the mobile phase can dissolve the ink and move it up the plate

how would the mp of an organic compound be affected if there were a shard of glass inside the mp capillary? explain.

the mp range would NOT be affected. NORMALLY, the addition of an impurity to a pure substance would depress/broaden the melting point range. HOWEVER, since the glass does not have any solubility in the liquid phase of the organic material, it would not change the observed mp range.

for theoretical plates in gas chromatography [GC] cloumn: what affects the number of theoretical plates in the column?

the rate of heating ...affects the number of theoretical plates in the column

A sep funnel contains the two immiscible liquids water and diethyl ether. Use the densities to determine which layer is on top. diethyl ether: 0.71 g/mL water: 0.998 g/mL

top: diethyl ether bottom: water

for oxidation od cyclohexanol to cyclohexanone, what is the procedure to.... test for the presence of oxidizing agent?

touch a drop of the reaction mix into a piece of KI-starch paper

The following statement describes possible compounds that might have be steam distilled with eugenol in the preparation clove oil, but then would remain in the organic phase when extracted with base. Identify the statement as true or false and explain answer: "there could be long-chain hydrocarbons"

true these are non-polar

Identify the atoms that participate in the 1,3-diaxial interactions of cis-1,2-dimethylcyclohexane. How many 1,3-diaxial interactions are present in the molecule?

two

For separation and collection of a two-component liquid mixture by prep GC: what is the procedure to... to avoid dangerous vibration due to imbalance in the centrifuge?

vials are place into the centrifuge in pairs, 180 degrees apart

For separation and collection of a two-component liquid mixture by prep GC: what is the procedure to... to preserve the purity of the sample because there is a lag between being detected and being eluted?

wait for the second peak to be on the rise before beginning its collection

For the chemically active solvent extraction of a three‑component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolved in dichloromethane: what is the procedure to...convert the benzoic acid into a water-soluble salt?

add aqueous BASE to the mixture dissolved in DCM

for oxidation od cyclohexanol to cyclohexanone, what is the procedure to.... generate the oxidizing agent?

add bleach dropwise into a flask containing acetic acid

( hypochlorite and glacial acetic acid react to make hypochlorous acid, which then oxidizes cyclohexanol to cyclohexanone. Aat the end of the reaction, any excess hypochlorous acid is neutralized) How is the HOCl neutralized

add sodium bisulfite, NaHSO3

for oxidation od cyclohexanol to cyclohexanone, what is the procedure to.... destroy the oxidizing agent?

add soidum bisulfite solution

the reaction of bromine and of permangante with cyclohexene both belong to which of the four general kinds of reactions?

addition rxn

the dehydration of an alkene with an acid yields...

alkene and water

identify the purpose of each step in the procedure for the reaction of 2-naphthol with allyl bromide and a phase transfer catalyst in strong base. what is the procedure to accomplish.... keep the time needed to complete the rxn under an hour?

allyl bromide was use din excess

during a solvent extraction between water and an immiscible solvent, a student has two layers in their sep funnel and then shakes it. A single, mily liquid develops and NO real sign of any layers are visible. what has occurred and what should the student do?

an emulsion formed -the student should first add a small quantity of water -if this does not work, the student should add more solvent

The carrier gas in a GC is usually...

an inert gas such as nitrogen, helium, or argon

Why is TLC a poor technique for the analysis of low boiling liquids?

if a liquid has a low boiling point, it will evaporate at room temp, before performing the TLC. Therefore, no spots will show up and the Rf value would not be calculated

The contamination of a pure organic with an impurity affect the observed melting point only if the impurity dissolves to some extent in the liquid phase of the organic compound. Therefore, small granules of sand or broken glass [sand and glass have similar compositions, melt only at very high temps, and are totally insoluble] will not reduce the melting point of a pure organic compound with witch they will be mixed. In a sample containing small grains of sand, what would you observe in the mel-temp apparatus when you melt the sample that would indicate that the melted sample contained this type of impurity?

if a sample of small granules of sand mixed with a pure organic compound, then only the organic compound would melt, leaving the sand/glass in a liquified organic compound

when using a sep funnel: when can the stopcock be used to vent excess pressure?

if ether of the liquids is warm to the touch and has a low boiling point

why is it not possible use ethanol to extract an organic compound from water even though most organics are more soluble in ethanol than water?

if the organic compounds were dissolved in ethanol, they would be a lot more difficult to separate/extract from the solution. *** the ethanol is MISCIBLE with water

limonene is the natural product found in orange peel. Choose the major product of the reaction of limonene with bromine under the conditions shown

limonene contains 2 double bonds. EACH of the pi bonds react with bromine by electrophilic addition. the bromines add across the double bond to produce the tetrabromo product

.Explain the direction in which the reaction time would change for a substance in a GC experiment when the exp parameters are changes as shown below: column temperature increase?

longer peaks AND retention time bc the compound isn't evaporating from the solution as fast

fractioning towers in a refinery can be identified as tall thin towers. Why are they always tall and narrow rather than short and wide? [w/ same vol.]

longer towers means more theoretical plates. More theoretical plates means better separation of the cmpds with similar boiling points

What would be the effect on temp observed during distillation if the thermocouple was placed near the top of the collection bulb rather than near the top of the column portion of the distillation head?

lowered if the thermocouple was near the top, it would not detect the temp of the vapor freshly boiled

write the equations of the chemical reactions that you used to show the presence of carbon-carbon double bonds in your products. show all products and indicate how you determined whether the reaction had occurred... for baeyer's test

postitive result showed the purple color disappearing and a brown precipitate forming

hydogen gas can also be used as a carrier gas for GC: What are the pros [3] and cons [1]?

pros: -cheaper than helium -can be gernated at the GC instead of from gas tanks -greater differences in mass between carrier gas and sample than nitrogen CONS: -explosion hazard

The williamson ether synthesis between 2-naphthol and allyl bromide in the presence of strong based and benzyktriphenylammoniumchloride as a phase transpher catalyst in DCM solution is known to proceed in reasonable yield. reagents? products?

reagents: NaOH and PhCH2(Bu)3NCl products: allyl bromide, allyl 2-naphthyl ether, and 2-naphthol

in this reaction, we are actually measuring the rate of formation of the carbocation intermediate [slow step]. it would be possible for he carbocation teo proceed to a product other than alcohol without changing our kinetics calculation. write the structure of other organic products that might be produced from the carbocation intermediate in this reaction.

see 11 https://drive.google.com/file/d/1K6N623Mrmj6VZhRM6IbrIQ9LR7mOlbyd/view?usp=sharing

During the recrystallization of a solid, the sample is dissolved in hot solvent then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a 2nd time. What effect will result if the filtrate solution is cooled too rapidly?

small IMPURE crystals are formed

identify the purpose of each step in the procedure for the reaction of 2-naphthol with allyl bromide and a phase transfer catalyst in strong base. what is the procedure to accomplish.... deprotonate alcohols to become good alkoxide nucleophiles?

solid sodium hydroxide was added to 2-naphthol

what two key factors does solvent extraction depend on for the solute and solvents?

solvent extraction works on the basis of a difference in solubility of a solute between two immiscible solvents

A TLC plate was run in 1:1 [hexane:tetrahydrofuran] but when developed, the plate only showed baseline spots. What change could be made to get the spots to move further up the plate?

spot a new plate and run in 1:4 [hexane:hydrofuran] because: all spots move further as the polarity of the mobile phase increases for THIS reaction THUS, switching to a solvent system that includes MORE tetrahydrofuran than hexane will allow the spots to separate from each other and from the baseline

the solubility of acetanilide is 18.5 g in 100mL of methanol at 0 C, and 59.2 g in 100 mL at 60 C. What is the MAX percent recovery that can be achieved for the recrystallization of acetanilide from methanol? [explain calculation method]

steps: 68.8% 1. If 59.2 is dissolved completely at 60 C... , when it is allowed to cool, there will still ne 18.5 g dissolved 59.2-18.5 = 40.7 g in solid form 2. Compare this to the original 59.2 g used. [ 40.7 / 59.2 ] * 100 = 68.8%

For Eugenol, what is the structure? what is its precursor? what type of secondary metabolite is it?

structure: [image] precursor: acetyl coenzyme A 2nd-Metabolite: Acetogin -essential oil found in cloves

For Limonen, what is the structure? what is its precursor? what type of secondary metabolite is it?

structure: [image] precursor: isopentyl diphosphate percursor 2nd-Metabolite: terpene

vapor-liquid composition curve: with each vaporization and condensation step enriches the [ lower OR higher ] boiling liquid in the VAPOR?

the LOWER boiling liquid is in the vapor

Finish the statements about Rf values: When more than one compound is present in a sample, the Rf values should be kept in the range of [ .... ] for the most effective separation

the Rf value range should be within 0.2 to 0.8

define density as applied to organic compounds?

the amount of mass [g] in a volume of cm^3

why is it important to wash your flask and collected crystals with ICE COLD solvent after recrystallization? what would happen if you used room temp or warm solvent instead?

the cold water allows the product to remain in crystal form rinsing it with warm water causes the crystals to melt into liquid form

How does a eutectic mixture affect the melting point?

the composition of a mixture of two compounds that generates the LOWEST possible melting point

What type of volatility must a mixture be in order to have a successful result from simple distillation?

the compounds in the mixture must have very DIFFERENT volatilities

identify the purpose of each step in the procedure for the reaction of 2-naphthol with allyl bromide and a phase transfer catalyst in strong base. what is the procedure to accomplish.... separate the nonpolar ether product from the polar products?

the contents of the rxn flask were passed through a column of silica

For separation and collection of a two-component liquid mixture by prep GC: what is the procedure to... to avoid loss of the sample?

the detector fitted to the prep GC is a TCD not a FID

for recrystallization: for hot vacuum, what should be done RIGHT before pouring the hot solution into the Buchner funnel filter

the filter paper should be dampened with hot solvent to ensure that the paper is not swept away when the hot solution is poured in -this would result in an impure filtration

which, if any, of the fraction s you obtained from each of these two distillations conducted in this experiment had boiling point ranges and gas chromatogram that would suggest that the these fractions were primarily one component? what was the largest ratio observed for the two compounds in these fractions?

1. -hexane was probably the primary compound in the first fraction bc as soon as it began to boil, it was collected in the distillation jar. -Since octane's bp was higher, it was the primary compound in the 4th fraction, when the temp was higher. 2. hexane had its lragest ratio in the first vial with a 96.9 : 1.6111 ratio, and octane had its largest ratio of 94.6:5.35 in the 4th fraction

The IR spectrum displays the wavelengths at which specific functional groups absorb energy. Which wavelength do each of these bonds absorb energy? 1. O-H [alcohol] 2. C--O [aldehyde]

1. 4000-3000 cm-1 2. 1800-1640 cm-1

Give two ways that infrared spectrophotometer fitted with an ATR sample IS advantageous over beam-through-sample spectrophotometer?

1. ATR allows for use of very small samples 2. sample preparation and clean up of an ATR is simple 3.

What is an oxidizing agent? what are 2 common oxidizing agents?

1. An oxidizing agent, or oxidant, gains electrons and is reduced in a chemical reaction 2. chromic acid and sodium dichromate

The IR spectrum displays the wavelengths at which specific functional groups absorb energy. Which wavelength do each of these bonds absorb energy? 1. C--C [alkene] 2. C--O [ester] 3. O-H [carboxylic acid]

1. C--C: 1600 cm-1 2. C--O: 1800-1460 cm-1 3. O-H: 4000-3000 cm-1

while doing a solvent extraction, you forget which layer is aqueous and which is organic. How can you easily determine the aqueous layer?

add a drop of water and see which layer it adds to

are eutectic mixtures always in a 1:1 ratio? can eutectic mixtures dissolve in one another?

1. NO 2. usually

Do beam-through-sample techniques... 1. have problems with nonpolar solvents? 2. require very expensive ZnSe sample holders? exaplain

1. No - they can do polar/nonpolar equally 2. No - ATRs require the expensive ZnSe crystals

Answer the questions about TLC: what can you use to mark the position of a spot? when should you mark the plate?

1. ONLY a pencil 2. mark the plate BEFORE applying the sample

list the 6 steps required to convert 1-chloro-1-phenyl ethane into 1-phenylethanol via SN1 solvolysis in water:

1. add a few drops of bromothymol blue to a stirred solution of ethanol and water 2. add NaOH solution from a burette. Note the volume. 3. record the time it takes for the solution to turn green 4. repeat the process of adding aliquots of measured base, and recording the time taken for a color change 5. heat on a steam bath above 50 C for 26 min 6. Titrate the contents of the flask against NaOH and record the final volume of the buret

for recrystallization: as the solution cools for recrystallization of the compound, what three steps should take if an OIL forms? what step should you NOT do?

1. add a small amount of water to the flask as the solution cools 2. reheat the solution gently until the oil dissolves 3. once dissolved, allow the solution to cool slowly note: do NOT place the solution with oil in an ice-water bath

list the seven steps of TLC separation [hint: add, make, use, stand, remove, mark, measure]

1. add just enough developing solvent to cover the bottom 3mm of the TLC chamber. Cover with a watch glass OR lid 2. make a pencil mark on the TLC plate 10 mm from the bottom. 3. use a capillary to deliver a 2mm diameter spot in the pencil mark 4. stand the TLC plate upright in the chamber, replace the lid 5. remove the plate when the solvent is near the top of the plate, and immediately mark the solvent front 6. mark the outline of the spots on the plate w/ a pencil 7. measure the distance the spot and solvent have moved [calc Rf values]

what type of agent is Bromine? what are three precations for bromine?

1. bromine is an oxidizing agent 2. causes skin burns, can be fatal if inhaled, must wear gloves

list the 7 steps that are requied to separate and collect a two-liquid mixture using prep GC (hint: collect, inject, slip, remove, add, transfer, centrifuge]

1. collect a vial of unknown mixture, record its number and letter 2.inject the mix into the numbered preparative GC instrument that matches the number of you vial 3. slip a collection tube over the lower exit port of the prep GC just after the first fraction begins to elute 4. remove the collection tube when the first peak is almost finished 5. add another collection tube, and take a center cut for the next fraction 6. transfer the sample to conical vials by connecting the vials to the collecting tubes 7. centrifuge both vials to collect the samples. cap the vials.

What 4 steps are used to separate eugenol from a mixture of other non-acidic molecules?

1. dissolve the mixture in dichloromethane 2. shake it with sodium hydroxide 3, collect the aqueous layer 4. reacidify to force precipitation of the eugenol

list the seven steps required to perform a chemically active solvent extraction of a three-component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule [all dissolved in dichloromethane]? (hint: dissolve, Add, separate, place, add, separate, collect]

1. dissolve the solid 3-component mixture in dichloromethane and place it in a sep funnel. Add 6 M HCl to the solution. Shake and allow to settle into layers 2. Add water to dissolve the brown emulsion btwn the layers 3. separate and collect the aqueous layer in a flask, and add base 4. place the DCM layer back in the sep funnel and extract it with 3 M NaOH. Allow layers to settle 5. Add water to dissolve the white gel-like emulsion 6. separate and collect the Aq. layer in a flask, and add acid 7. collect and dry the solids in both erlenmeyer flasks by filtration

a sample of an unknown compound has a mass of 22.30 g, and a volume of 5.47 mL. what is the density of a liquid? explain steps

1. divide its mass by its volume [ make sure its in g/mL] 22.30 g / 5.47 mL = 4.08 g/mL

for a sucessful TLC experiment, it is important to pay attention to the details. What are the top 4 things to remeber for TLC?

1. do NOT disturb the chamber, no moving 2. draw a starting line and mark the compounds' spots with a plain pencil, no pen or marker 3. cover the chamber with a glass/lid 4. ensure the solvent level in the chamber is lower than the starting line where you spot the samples note: no need to monitor temp

list the 7 steps to convert 2-napthol and allyl bromide into allyl 2-napthyl ether [hint: fit, add, cover, periodically, remove, run, and evaporate]

1. fit a concical vial with dichloromethane and add 2-naphthol, allyl bromide, and benzyltriammonium chloride in dichloromethane 2. Add sodium hydroxide to the rxn flask 3. cover the rxn vial and stir 4. periodically stop the stirring, allow the layers to settle, and spot the organic layer on a TLC plate 5. remove the bottom layer and dry over calcium chloride 6. run the rxn solution through a silica chromatography solumn 7. evaporate DCM solvent to dryness

which waste bin would each of these go to: 1. used mp capillaries 2. contaminated paper towels 3. Sodium bicarbonate solution 4. TLC solvent

1. glass 2. solid waste 3. 10% aqueous waste 4. hexanes, ethyl acetate, etc.

Answer the questions about TLC: what side of the plate is spotted? where on the plate can you touch? how large should the spots be?

1. in the dull [not shiny] side 2. only touch the edges 3. the spots should be 1-2 mm in diameter

what are two things that can be done to the column to produce MORE theoretical plates?

1. increasing the length of the column 2. packing the column with glass beads or rings

what does rapid heating do to the gas chromatography process? [4 points]

1. it can drive heated vapor up the column 2.^This prevents the formation of an equilibrium that allows the lower boiling component to separate 3. DECREASES the number of theoretical plates 4. DECREASES separation :-(

For Eugenol: is it soluble in water? what makes it dramatically more acidic than regular straight-chain alcohols?

1. it is NOT soluble in water 2. the ALCOHOL group makes it more acidic

in order to preform a bromine test, what must be done? what indicates a positive result?

1. it must be treated with a dilute solution of bromine 2. the reddish color of the bromine will disappear

list the 8 steps required t convert cyclohexanol to cyclohexanone (hint: mix, add, maintain, remove, add, place, dry, and decant)

1. mix cyclohexanol and acetic acid in an Erlenmeyer flask 2. add bleach dropwise into the flask 3. Maintian the reaction temperature between 40-45 C on a steam bath 4. remove unused bleach with sodium bisulfite solution 5. add drops of 6 M NaOH until the solution is pH 6-8 6. place reaction in searpatory funnel and extract with dichloromethane 7. dry the dichloromethane layer over potassium carbonate 8. decant from the potassium carbonate and collect by distillation

list the seven steps of recrystallization [hint: place, add, rapidly, wash, allow, vacuum, air]

1. place the impure substance and a boiling chip into an erlenmyer flask on a heating element 2. Add the minimum amount of hot water to just dissolve the solid 3. rapidly filter the hot solution through a pre-warmed funnel 4. wash the filter with hot solvent and transfer the filtrate to a clean flask 5. Allow the filtrate to cool slowly, then cool in an ice bath to force precipitation 6. Vacuum filter the COLD suspension 7. Air dry the purified solid on the filter

List the 7 steps in order for performing a melting point determination

1. press the open end of a capillary tube into the solid sample 2. invert the tube and tap gently to move the solid to the bottom of the capillary 3. place the tube with the sample into the mel-temp and heat at 10 C/min 4. observe the material through the complete melting point process to get a rough estimate of the melting point range 5. turn off the and allow to coll by 15 degrees below mp range 6. replace the existing tube with a new sample 7. heat at 2 C/min through the expected mp range

what types of alcohols can be oxidized? what would they be oxidized to? (2) Which can NOT be oxidized?

1. primary and secondary 2. primary becomes carboxylix acids and secondary become ketones 3. tertiary canNOT be oxidized

Rules for TLC: fill in the blank 1. when the solvent has reached the correct height, (______) 2. TLC date is interpreted in terms of (______) 2. do NOT allow the solvent to get within (______)mm of the top of the plate

1. remove the plate from the chamber and immediately draw a line at the solvent Front 2. Rf values 3. 1-2 mm

what types of substances can have AZEOTROPES? 1. properties? 2. number of components in mix?

1. substances that have SIMILAR properties [like ehtanol and water] ANS those that have DIFFerent properties [toluene and water] 2. between two liquids AND between mixes of 3 or 4 compounds

Rules for TLC: [fill in the blank:] 1. in the beginning, the solvent level should be below (______) 2. do not allow (______) to touch the filter paper 3. allow the solvent to get with in (______)mm of the top of the plate

1. the marked spots/origin 2. bottom of the filter paper 3. 5-10 mm

A 0.7 mL mix of pentanol and heptanol are separated and collected using preparative GC on a GC fitted with a polar column and a TCD detector: during the separation, what 2 reasons are there for why the injection port and detector are heated to a higher temperature than the column? and explain

1. the wire in the thermal conductivity detector needs to be cooled by the eluent in order to register a signal -the thermal conductive detector is operated at a high temp so that the eluent can effectively cool the TCD wire to register a signal 2. a heated injector creates flash vaporization which allows for separation at temperatures lower than the boiling point of the sample. -this avoids issues with thermally unstable molecules

give two reasons why moisture must be excluded from any sample injected into the GC:

1. water contains dissolved salts that can clog the injector 2. water is very slow to elute from the column

Eugenol, the essential oil found in cloves, can be isolated by steam distillation bc it is insoluble in water and has a much higher boiling point: eugenol bp: 254 C VP at 100 C: 4 mmHg MM: 164 g/mol DENSITY: 1.05 g/mL Water BP: 100 C VP at 100 C: 760 mmHg MM: 18 g/mol DENSITY: 1.00 g/mL Based on this info, calculate the volume of eugenol in 30 mL of distillate

1.3 mL 1. calculate mole fraction 2. calculate V% of eugenol 3. multiple by total volume see sap :-/

what solvent has the highest eluting power for the analgesics analyzed in this experiment? which solvent had the lowest eluting power?

100% EtOAc had the highest eluting power, and hexane had the lowest

What region if the IR spectrum is best used for distinguishing between isomers that have the same functional groups?

1400-400 cm-1

of these three molecules, which is the LEAST soluble in HOT water? salicyclic acid, acetaminophen, and 2-naphthol

2-napthol -it has the lowest ratio of hyrdrogen bonding components [polar protic] to hydrocarbon [non-polar] character. -it will no be very soluble in water under any conditions

Soaps are sodium or potassium salts of long chain (18+ carbons) carboxylix acids. They dissolve grease by forming micelles that are water soluble because the anionic carboxylic acid groups are on the outside solvated by water while the inside micelle contains long hydrocarbon chains. Oils and greases are dissolved into the oily middle of the micelle and are washed away. If you wanted to design a quaternary ammonium salt that would make for a great soap [with a positive charged, water soluble nitrogen group], what type of R groups would you want to attach to the nitrogen?

3 of the R groups on the N should be replaced with long-chain carbon groups (18+ cabrons). this would provide a nonpolar area on the molecule. the 4th r group should a carboxylic acid group. this would give this side of the molecule a polar region

Azeotrope Definition

A liquid mixture of two or more substances that has its own constant boiling point, different from the boiling points of its constituents. The vapor of this unique mixture has the same composition as the liquid state, making it difficult to separate the constituents..

(Eugenol, the essential oil found in cloves, can be isolated by steam distillation bc it is insoluble in water and has a much higher boiling point: eugenol bp: 254 C VP at 100 C: 4 mmHg MM: 164 g/mol Water BP: 100 C VP at 100 C: 760 mmHg MM: 18 g/mol ) Use this infor to calculate the mole fraction, Xorg, of eugenol in the distillate...

A mixture boils when total vapor pressure equals atomospheric: P total = Porg + P water = 760 mmHg Xorg = VPorg / (VP of organic + water) X org = 4 / (760) = 0.0053

Infrared spectra are recorded using an ATR detector. What does ATR stand for?

Attenuated total reflectance

How can you determine the boiling point of a mixture?

Because mixtures of immmiscible liquids do not obey Raoult's law, the bp of the mix depends only on the vapor pressure if the components and no on their mole fraction. the clausius-clapeyron equation can be used to calculate the temp at which water boils unders a partial vacuum of 4 mmHg equation: ln[P2/P1] = [(delta H of H2O vapor)/R] * [(1/T1)-(1/T2)] Solving for T2 will give the NEW boiling point

why is the reaction of alkenes with HCl NOT useful as a characterization reaction, but Br2 is a good reaction?

Br2 will yield a visable color change

How is gas chromatography [GC] able to separate two liquids with the exact SAME boiling point, but fractional distillation cannot?

GC: the use of a polar GC column will separate the liquids based in differences in polar interactions and volatility

For very accurate determination of melting points, scientists use thermometers that have been calibrated by measuring the melting points of known standards. You did not calibrate your thermocouple. What data obtained during this experiment allows you to be confident that the thermometer system you were using was not giving readings that were inaccurate by 10 degrees or more? (What material with a known mp did you determine a mp?)

During this experiment, the melting points of the standards were used to make sure the system was giving accurate readings, because students could look at the chart of the known melting points and compare that their own findings of standard melting points ***Standards usually mixed with unknown, which brings uncertainty better example was the benzoic acid and sand [bc sand doesn't affect mp]

The gauche conformation of butane occurs when the dihedral angle between at the C1-C2 and C3-C4 is 60 degrees. There is sterric strain in the molecule due the proximity of the two methyl groups. When you consider... E(strain) = E(strain) + E(angle) + E(torsion) + E(sterric) Would E(torsion) increase OR decrease when the dihedral angle of gauche butane was increased from 60 to 65 degrees?

E(torsion) increases [torsional strain]

[clove oil is produced by steam distillation of cloves. the basic extraction of clove oil to obtain eugenol leaves behind other organic products.] The following statement describes possible compounds that might have be steam distilled with eugenol in the preparation clove oil, but then would remain in the organic phase when extracted with base. Identify the statement as true or false and explain answer: "they might contain large numbers of -OH functional groups"

FALSE These would be polar and not be in the organic layer

(An over-the-counter headache pill was crushed, extracted into ethanol/dichloromethane, and then analyzed by TLC on silica using ethyl acetate as an eluent. the pill was shown to contain: acetaminophen, aspirin, and ibuprofen.) Rank the Rf values of acetaminophen, aspirin, and ibuprofen:

Highest to lowest: ibuprofen, aspirin, and acetaminophen the less polar = the less it sticks to the silica = the more it moves = the higher the Rf value

What type of samples is IR not the best at detecting?

IR is not the best for detecting samples with complex MIXTURES. The spectrum would be overly complicated with the bond frequencies of all the different. complex molecules in the MIXture.

in a solution of water and ethyl acetate: top layer? bottom layer?

top layer - ethyl acetate bottom layer - water

the boiling point of an AZEOTROPE is [ lower OR higher ] than either of the pure substances it is composed of?

LOWER

what are the 4 major methods of purification in chem lab? which is definitely NOT one?

Major 4: distillation, extraction, recrystallization, and chromatography [NOT subtraction]

What causes a carbotcation to be more stable?

More substitution: Alkyl groups are better able to donate electron density than are hydrogen atoms. Thus, the positive charge is stabilized better by alkyl groups, so a great number of CH3 goups provides more stability for the positively charged species. Th tertiary carbocation is the most stable species. followed by the secondary and then primary carbocations. The methyl cation is the least stable [CH3+]

An over-the-counter headache pill was crushed, extracted into ethanol/dichloromethane, and then analyzed by TLC on silica using ethyl acetate as an eluent. the pill was shown to contain: acetaminophen, aspirin, and ibuprofen. Between acetaminophen, aspirin, and ibuprofen, which molecule is the most polar? Least Polar?

Most = Acetaminophen the hydroxyl group and amide group in acetaminophen as well as the carboxyl group in aspirin and ibuprofen are he only groups in these compounds that are capable of both making recieving bonds. Acetaminophen is the MOST polar bc it has two of the hydrogen bonding groups. least = ibuprofen other oxygen groups, such as ketones and esters, contribute to polarity to a lesser extent. Aspirin is the more polar than ibuprofen bc it has other oxygen groups in addition to the carboxyl group. Therefore, ibuprofen must be the LEAST polar molecule since it includes only one polar carboxyl group and the rest of the molecule is made up of nonpolar hydrocarbons

Benzoic acid and Benzocaine dissolve really well in ethanol. Is ethanol a suitable solvent for the solvent extraction of benzoic acid and benzocaine from aqueous solution?

NO ethanol is miscible with water [you would not be able to see the separate layers]

.Explain the direction in which the reaction time would change for a substance in a GC experiment when the exp parameters are changes as shown below: detector temp increased by 10 C

NO change of retention time: the temp would just increase by 10 C

for recrystallization: is rapid cooling good for producing the best crystals?

NOO

What is the risk for each of these NaOH? lachrymators like allyl bromide? dichloromethane?

NaOH can cause severe damge to skin and eyes [gloves and goggles are required] allyl bromide is irritant to the eyes and is bad for the environment [does NOT go in aqueous waste] dichloromethane is a carcinogen

is distillation a chemical or physical reaction?

PHYSICAL

What is an Rf value? [what does it describe?]

Rf = retention factor This is a number that describes the position of a spot on a chromatography plate relative to the position if the solvent on the chromatography plate.

identify which layer of a solution would each of the compounds dissolve into: allyl 2-naphthol ether, sodium hydroxide, water, allyl bromide, aqueous layer, dichloromethane, benzyltributylammonium chloride, organic layer and sodium 2-naphtholate

TOP: aqueous layer... sodium hydroxide, water, sodium 2-naphtholate, and benzyltributylammonium chloride BOTTOM: organic layer allyl 2-naphthol ether, allyl bromide, dichloromethane, and benzyltributylammonium chloride

The following statement describes possible compounds that might have be steam distilled with eugenol in the preparation clove oil, but then would remain in the organic phase when extracted with base. Identify the statement as true or false and explain answer: Methyl eugenol could be present

TRUE nonpolar???????

Both Br2 and HCL undergo electrophilic addition to alkenes. Why is Br2 used as a test for unsaturation instead of HCL?

The reaction with bromine can be follwoed bc of a visible loss of color

What property of the substrate in SN1 reactions make it go faster? List the following with their speed in an SN1 reaction: 3-iodo-2-methylhexane 2-iodo-2-methylhexane iodomethane 1-iodo-2-methylhexane

The slow step of an SN1 rxn is the breakage of teh carbon-halogen bond and formation of a carbocation. The more stable the carbocation, the faster the reaction. Therefore, the fastest SN1 substitution occurs in tertiary alkyl halides, and the slowest are with primary, methyl halides. 2-iodo-2-methylhexane > 3-iodo-2-methylhexane > 1-iodo-2-methylhexane > iodomethane

what is the purpose of a hot filtration when performing a recrystallization?

This filters out only the solid impurities. the acetanilide stays dissolved in the solution, since it is able to dissove at relatively high temperatures [while the impurities cannot]

when is it is possible to use GC two separate two liquids that have identical boiling points and which show no separation by distillation [even fractional distillation]?

This is possible when the compounds have different functional groups, that give them different polarities. These cmpds cannot be separated if they have the same FGs and BPs

in a solution of water and dichloromethane: top layer? bottom layer?

top layer - water bottom layer - dichloromethane

Are Rf values dependent on polarity? explain

YES... Polar compounds will have LOWER Rf values NON polar compounds will have HIGHER Rf values

For the chemically active solvent extraction of a three‑component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolved in dichloromethane: what is the procedure to... to precipitate the benzocaine?

add BASE to the aqueous acidic layer mix

A student is comparing two samples of crystalline organic solids. A thin-layer chromatography analysis shows a single spot for each sample and the co-spot with the same Rf value. What method would provide the most conclusive evidence that the two samples are the same compound? [list 3 that would NOT work]

YES: Perform a mixture melting point... this will identify if the 2 samples have the same identity or not. The introduction of an impurity results in depression of the melting point DO NOT: running TLC on avlonger plate or with more development solvent is not effective since Rf values are independent of length or volume of solvent. mixing substance to run the TLC as a single spot will only give the same results as before.

for recrystallization: what is the formula for calc percent yield?

[(mass after recrystal-)/(initial mass)] * 100

how do calculate Rf values?

[distance traveled from the origin by the spot] / [dist. traveled by the solvent]

How can the boiling point difference affect the number of theoretical plates needed? [and how does it affect the overall separation?]

a LARGER bp difference allows for easier separation and fewer theoretical plates needed :-)

write the equations of the chemical reactions that you used to show the presence of carbon-carbon double bonds in your products. show all products and indicate how you determined whether the reaction had occurred... for bromine

a positive test resulted in the the dark orange color of bromine disappearing

During a melting point determination, is it normal to first take a rapid rough measurement followed by a slower more accurate measurement. Why is it important to allow the Mel-temp to cool 15 C below the mp before placing the 2nd capillary tube in, and to set the voltage to generate 1-2 C/min through the mp range?

a rapid temperature increase would give a melting point range that is much higher than the true value

for recrystallization: the material to be purified must be a (...)

a solid

during thin layer chromatography, what method [tool] is used to apply the dilute solution of the sample to a TLC plate?

a thin, glass spotter or capillary tube

for gas chromatography: what is the stationary phase?

a very high-boiling liquid absorbed into fire brick

how did you deduce which spot corresponded to 2-naphthol on your tlc plate that analyzed the reaction mixture at 10,30, and 60 min? did you tlc analysis indicate the presenc eof 2-naphthol at the end of the 60 min rxn time?

a. the 2-naphthol was the compound with the lower Rf value [bc its polar], and its intensity decreased over the course of the 60 min period b. the TLC did not detect the presence on 2-naphthol on the 60 min tlc plate

The simple distillation set up used in this experiment has about one theoretical plate. see the table in the link to estimate the minimum boiling point difference btwn 2 cmpds that would allow effective separation by simple distillation: https://drive.google.com/open?id=1bAsPMiQhuAOx2cjeelus4XiVyUOU-Inn

about 40-45 C the larger the temp difference btwn 2 cmpds with 1 theoretical plate, the larger the amount of difference in temperature needed to have 98% efficiency

For the chemically active solvent extraction of a three‑component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolved in dichloromethane: what is the procedure to... convert the benzocaine into a water-soluble salt?

add ACID to the 3-component mix

The williamson ether synthesis between 2-naphthol and allyl bromide in the presence of strong based and benzyktriphenylammoniumchloride as a phase transpher catalyst in DCM solution is known to proceed in reasonable yield. why will the reaction fail to work if the solvent is switched to ethanol while retaining the same reactants, phase transfer catalyst and base?

bc the base would deprotonate ethanol and create a 2nd nucleophile note: 2-naphthol is converted to alkoxide nucleophile by base. if the solvent is also an alcohol, a 2nd nucleophile would be introduced into the rxn

The williamson ether synthesis between 2-naphthol and allyl bromide in the presence of strong based and benzyktriphenylammoniumchloride as a phase transpher catalyst in DCM solution is known to proceed in reasonable yield. the need for a phase transfer catalyst would be removed if a polar Aprotic solvent [such as DMSO] were used as a rxn solvent. why is DMSO not used as a solvent for this rxn?

bc the risks associated with toxicity

Use the melting point phase diagram: If you compare the melting point of a slightly impure mixture with the melting point of a eutectic mixture, the melting point of the slightly impure mixture will be: Explain why.

broader and higher than the eutectic mixture when a eutectic mixture is melted, it would melt at the lowest temp observed for the mix of the two compounds. Eutectic mixtures also produce sarp melting points, so the slightly impure mixture melting point would be broader and higher

how is recrystallization able to remove impurities for an impure compound?

by exploiting differences in solubility between hot and cold solutions. $ - The impure compound is dissolved in a WARMER solute and then COOLED slowly to form crystals with higher purity

Why do SN1 reactions prefer polar protic solvents?

carbocation intermediates are stabilized by protic solvents like water

products from any of the possible alcohols will show similar absorption bands characteristic of two types of bond-stretching in the functional group region. What are these two bond types?

carbonyl C--O stretch [1670-1830 cm-1] and sp3 C-H bond stretch [2850-2960 cm-1]

for oxidation od cyclohexanol to cyclohexanone, what is the procedure to.... dry the reaction product?

combine the organic layers over anhydrous potassium carbonate

.Explain the direction in which the reaction time would change for a substance in a GC experiment when the exp parameters are changes as shown below: carrier gas flow increase?

decreases bc it's going through the machine faster

A williamson ether synthesis between 2-naphthol and allyl bromide is performed in the presence of a phase transfer catalyst and a strong base in DCM solution. The rxn mix contains unreaction allyl bromide, unreacted 2-naphthol, benzyltributylammonium chloride, allyl naphthyl ether, and DCM. The rxn mix is passed through a silica gel MINI-COLUMN. What is drained through [leaves] the mini-collumn?

dichloromethane and allyl naphthyl ether

Consider the result if we heated a mix of DCM (bp 39-40 C) and naphthalene ( bp 218 C) to 60 C until distillation stopped, and then cooled the flask to room temp. what would be in the distillate and what would be in the distillation flask?

distillate: DCM bc it has a bp below 60 C dist-flask: naphthalene bc it has a bp much higher than 60 C

For separation and collection of a two-component liquid mixture by prep GC: what is the procedure to... avoid the introduction of a spurious peak into the GC trace

do not rinse the syringe with acetone, rinse it with the sample instead

what is a theoretical plate

each vaporization-condensation

identify the purpose of each step in the procedure for the reaction of 2-naphthol with allyl bromide and a phase transfer catalyst in strong base. what is the procedure to accomplish.... remove dissolved water is from the rxn mixture? [dry the solution?]

enough calcium chloride to cover half the bottom of the flask was added

Which tests Cyclohexene positive for: ferric chloride: bromine: potassium permanganate:

ferric chloride: NO bromine: YES potassium permanganate: YES

Which tests IS Limonene positive for: ferric chloride: bromine: potassium permanganate:

ferric chloride: NO bromine: YES potassium permanganate: YES

Which tests is eugenol positive for: ferric chloride: bromine: potassium permanganate:

ferric chloride: YES bromine: YES potassium permanganate: YES

arrange the following SOLVENTS from least to most dense: chloroform, dichloromethane, diethyl ether, hexanes, and water

hexanes < diethyl ether < water < dichloromethane < chloroform

explain how pure samples of each compound can be obtained by prep GC from a mix of 2 cmpds even if complete resolution of the peaks is not obtained.

in order to keep the samples pure when the peaks overlap, we would have to only collect samples when the peaks are separated. therefore, using only the start of the first peak and the end of the second even though some of the mix is lost, the samples extracted are more likely to be pure

.Explain the direction in which the reaction time would change for a substance in a GC experiment when the exp parameters are changes as shown below:' concentration of stationary phase liquid increase?

increases retention time bc the solution is spending more time in the machine

for an IR spectrum: what type of electromagnetic radiation is associated with the peaks in this column?

infrared radiation

What is the cautionary detail for each of these: is silica toxic? is hexane flammable is ethyl acetate flammable? is acetone flammable? can you handle TLC plates with bare hands?

is silica toxic? NO is hexane flammable? YES is ethyl acetate flammable? YES is acetone flammable? YES can you handle TLC plates with bare hands? NO

Over time, what happens to the amount of the MOST VOLATILE component in the distillation flask?

it DECREASES

what is the purpose of the bromine test

it is an effective method for identifyin th presence of alkenes and alkynes. For this test, a solution containing 3 drops of a compound is treated with a dilute solution of bromine when the bromine undergoes an addition reaction with the double bond in an alkene or the triple bond in an alkyne, the reddish color of the bromine disappears, showing a positive test result

Why is it good to perform a mixed melting point determination at two different ratios of unknown to know material in the melting point capillary?

it is possible that one of the particular combinations of these two compounds can generate a eutectic mixture

During the development of a TLC plate, it is common to cover the chamber and have a piece of moist filter paper line the walls of the TLC chamber. What is the point of gaving the filter paper in the jar?

it is there to ensure that the air in the chamber is saturated with solvent vapor

For a pure substance, the melting temperature range is usually [ broader OR narrower] than that of an impure sample?

it is usually NARROWER

To get effective mizing in a sep funnel, the combined levels of liquids should not exceed what part of the funnnel?

it should not pass the highest part of the widest portion of the sep funnel

If a SOLVENT is made LESS polar, how will this affect the Rf values?

it will DECREASE the Rf values

(Eugenol, the essential oil found in cloves, can be isolated by steam distillation bc it is insoluble in water and has a much higher boiling point: eugenol bp: 254 C AND VP at 100 C: 4 mmHg Water BP: 100 C AND VP at 100 C: 760 mmHg Based on this info, at what temp will the mixture of eugenol and water boil?

less than 100 C liquid boil when their vapor pressure equals that of the atmospheric pressure [760 mmHg]. At 100 C, eugenol contributes 4 mmhg of vapor pressure to the total pressure of the mixture. This is an analogous to boiling water at a reduced pressure [756 mmHg]. This will induce a small depression in the boiling point, and the mix will boil at slightly less than 100 C [and significantly less than the bp of eugenol]. steam distillation is therefore useful for distilling high-boiling liquids that are immiscible in water. it is especially useful for distilling liquids that decompose near their BPs.

list 3 main ways to access the purity and identity of a substance

melting point determination, solubility tests, and thin-layer chromatography

how does equilibrium change affect the analyzed compound between gas phase and immobile liquid phase?

more time spent in immobile phase equal longer retention time

if concentrated sulfuric acid were spilled during the experiment, what is the proper procedure for cleaning the spill?

neutralize the spill with sodium bicarbonate

For the chemically active solvent extraction of a three‑component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolved in dichloromethane: what is the procedure to... to avoid spilling chemicals on others/yourself?

never point the sep funnel at anyone

.Explain the direction in which the reaction time would change for a substance in a GC experiment when the exp parameters are changes as shown below: amount of sample decreased by 20% from a sample that gives a good retention time?

no change: the amount of sample injected doesn't affect the retention time

does density directly correlate with molar mass?

no, density does NOT always increase as molar mass increases

is density directly related to molecular weight of a substance?

no, even though water (18 g/mol) has a smaller molar mass, it takes the more volume per gram compared to cyclohexane (84 g/mol). This likely due to other physical properties if the compound

write the mechanism for oxidation of an alcohol to a ketone using hypochlorous acid. What are the inorganic by-products of this reaction?

non organic by-products: HCl and water

organic compounds must exhibit what property in order to be visulaized on a TLC plate by the technique [UV light] used in the lab?

organic compounds must be able to absorb UV light or prevent the indicator from fluorescing

clove oil is produced by steam distillation of cloves. the basic extraction of clove oil to obtain eugenol leaves behind other organic products. what types of organic cmpds will not steam distill?

organic compounds that are soluble in water will not distill

For the chemically active solvent extraction of a three‑component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolved in dichloromethane: what is the procedure to... to recover a mixture in case a stopcock leaks

place a beaker below the sep funnel

for oxidation od cyclohexanol to cyclohexanone, what is the procedure to.... control the rate of the reaction?

place the reaction flask in an ice bath

Even if two compounds have identical solubility profiles in a solvent, it is possible to effect some purification by a single recrystallization. Assume you have a 10 g mixture of A and B in a 9:1 ration of A to B and that both have a solubility at room temperature of 0.1 g/mL. If you used 10 mL of solvent for recrystallization, how much B would be expected to be in the crystalline material if material was cooled to room temperature before filtration? (This calculation assumes an ideal recrystallization that probably wouldn't be totally true in a real experiment.) This allows you to determine the amounts of A and of B in the recrystallized solid. What is the ratio of A:B in the crystalized material (grams of A: grams of B)?

the ratio of A:B would be 8:0 because all of the B was able to dissolve (1 g/mL of the 1 g B added) in the solution at room temperature and would not have any left over to crystallize

what is density?

the ratio of a substance's mass to its volume, measured in grams per millimeter and ALSO equivalent to grams per cubic meter

what error is introduced if the bulb of the thermometer [thermocouple] is tooo high in the distillation apparatus?

the recorded boiling point will be lower than the actual BECAUSE the bulb is not exposed to the hot vapor

identify the purpose of each step in the procedure for the reaction of 2-naphthol with allyl bromide and a phase transfer catalyst in strong base. what is the procedure to accomplish.... avoid making the rxn mix become an emulsion?

the rxn was storred at a MODERATE, not rapid, pace

The gauche conformation of butane occurs when the dihedral angle between at the C1-C2 and C3-C4 is 60 degrees. There is sterric strain in the molecule due the proximity of the two methyl groups. Would the sterric strain in this molecule increase OR decrease C1-C2-C3 [and C2-C3-24] bond angle was increased to more than 109.5 degrees?

the sterric strain would decrease because the groups are moving farther apart

1-Phenyl-1-chloroethane is a secondary halide. Most secondary halides undergo Sn1 reaction quite slowly. Explain why 1-Phenyl-1-chloroethane undergoes Sn1 nsolvolysis quite readily. (Consider the mechanism shown above)

the structure we used has a benzene ring [w/ double bonds] allowing it to shift the positive charge around, giving it resonance stability. this stability makes it more willing to release the chloride originally, causing the rate to increase note: -because the carbocation is attatched to an arene so the resonance of the ring stabilizes the carbocation which results sn1 reaction

what is the appropriate response to an HCl spill on bare hands?

the student shpu;d telll the TA or instructor immediately and wash his/her hands with copius amounts of water in the sink

when using a sep funnel: if one is going to re-extract the upper layer with ANOTHER volume of liquid, what can you do with the first upper layer in the sep funnel

the upper layer can be left in the sep funnel and fresh solvent added to the funnel

For an IR spectrum: what is the measured spectroscopic method?

the vibral frequency of the bond

The Williamson ether synthesis between 2‑naphthol (MW 144.2 g/mol) and allyl bromide occurs in dichloromethane solution in the presence of the phase transfer catalyst, PhCH2(Bu)3NCl, and NaOH and produces allyl 2‑naphthyl ether (184.23 g/mol). A reaction was performed in which 0.43 g of 2‑naphthol was reacted with a slight excess of allyl bromide to make 0.48 g of allyl 2‑naphthyl ether. Calculate the theoretical yield [grams] and percent yield for this reaction. Allyl bromide has a density of 1.40 g/mL.

theoretical: 0.55 g percent yield: 87.3% First find the initial number of moles in 0.43 g of the limiting reactant, 2‑naphthol and calculate the moles of allyl naphthyl ether formed based on the 1:1 mole ratio. (0.43 g)(1 mol / 144.2 g) = 0.0030 mol 0.0030 mol 2‑naphthol = 0.0030 mol allyl naphthyl ether

the methylene chloride solution at the end of the reaction period may have a variety of materials in it (unreacted allyl bromide or naphathol, phase transfer catalyst, and allyl 2-naphthyl ether). what is expected to happen to the nahthol and phase transfer catalyst when the solution is passed through the silica gel mini-column?

these two compounds are polar and would "stick" to the SiOH polar molecules in the mini-column. This is so that only the non-polar products are likely to pass through (allyl-2-napthol and DCM).

describe how hypochlorite and glacial acetic acid react?

they react to make hypochlorous acid, which then oxidizes cyclohexanol to cyclohexanone. Aat the end of the reaction, any excess hypochlorous acid is neutralized

when using a sep funnel: how should a student close the sep funnel for shaking?

they should be sure to use a STOPPER to close/seal the sep funnel before shaking [do NOT use a thumb/finger to seal it]

why is extraction a good way to separate and purify a compound from a mix of organic material and inorganic salts?

this process bases its separation on the compounds being immiscible. The organic compounds dissolve in dichloromethane, while the inorganic salts dissolve in water. Therefore, as the water and DCM separate, so do the organic and inorganic cmpds.

rate of reactants [rate in rate equation] always have mole L-1 sec-1. in the above equation, what was the units of the rate constant, k?

time-

for recrystallization: why are clamps used to secure the filter flask?

to avoid tipping and unnecessary exposure to hot liquids or the solute

During the recrystallization of a solid, the sample is dissolved in hot solvent then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a 2nd time. What is the purpose of the initial hot vacuum filtration in the recrystallization process?

to remove Insoluble solid IMPURITIES

for SN1 solvolysis of tert-butyl chloride, rank the solvents from fastest to slowest rxn and explain WHY acetone, acetic acid, ethanol, formic acid, methanol, water

water> formic acid> methanol? ehtanol> acetone> acetic acid Because... needs to be polar protic A molecule of an alkyl halide ionizes to a postively charged carbocation and a negatively charged halide ion in the rate-determining step. A solvent with a high dieltric constant stabilizes the charge-separated transition state, lowers the activation energy, and increases the reaction

For the chemically active solvent extraction of a three‑component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolved in dichloromethane: what is the procedure to... to avoid a build up of pressure inside the glassware?

went the sep funnel via the stopcock

why is the reaction of cyclohexene with HBr [rapid, simple] not useful as a characterization reaction?

when HBr reacts with cyclohexene, the reaction is colorless further reactions would have to take placec to confirm the presence of cyclohexene

WHEN is recrystallization NOT a suitable method to purify an organic material?

when the organic material is a LIQUID instead of a solid

The vapor-liquid composition curve for a two component liquid mixture is shown below. Use the diagram to determine which of the follow statements are correct. Select all that apply.

yeah, idk