Ochem 1 lab final

What hazards are associated with naphthalene?

Naphthalene is flammable. Naphthalene is toxic. Naphthalene produces nauseating vapors.

Identify the characteristics of a good recrystallization solvent.

Dissolves a chemical sample well at high temperatures. Does not dissolve a chemical sample well at low temperatures.

Why should you use a finely ground solid when determining the melting point of a sample?

Air pockets in a coarse sample could disrupt heat distribution. Uniform, small particles heat more consistently throughout the sample.

When working in a fume hood, what is the best position of the hood sash?

As low as possible, no more than halfway up

How can a catalyst be recognized in a mechanism?

The catalyst is used and then regenerated in a later step.

Why might activated carbon be added to a sample during the recrystallization process?

To absorb impurities causing the recrystallization solution to have an incorrect color

What is the purpose of a drying agent in the work up of an organic reaction?

To absorb small amounts of water in an organic solution

What modifications to a fractional distillation setup can be made in order to increase the speed or efficiency of the separation?

Wrap aluminum foil around the sample flask and fractionating column. Place the receiving flask in an ice bath.

Once the separation is complete in a vacuum filtration, stop the process by first _______________ and then _________________________.

opening the clamp or stopper on the solvent trap ; turning off the vacuum source

The iodine test shows the presence of A positive iodine test appears as A negative iodine test appears as

starch a color chagne to blue-black a yellowish solution

An SN2 reaction is a type of ______________________ in which the nucleophile attacks the electrophile ________________ a leaving group leaves. The rate of the reaction depends on the concentration of _______________.

substitution reaction; at the same time ; both reactants

An azeotrope is a mixture that has _______ composition in the _________________. Therefore, an azeotropic mixture _________ be separated by distillation.

the same; gas and liquid phases; cannot

When sucrose is hydrolyzed, _________ will be created as the glycosidic linkage is broken. Hydrolyzed sucrose _______ give a positive Benedict's test. Hydrolysis can be achieved by adding ______________.

two reducing groups; will; strong acids or enzymes.

Recrystallization is a powerful purification technique but it can have some problems that will require you to adjust the procedure. Determine which problem each recrystallization procedure adjustment is trying to address. 1. Add activated charcoal and use hot filtration to remove it 2. Change to a recrystallization solvent with a lower boiling point 3. Heat the solution and pass it through the filter to dissolve crystals 4. Lightly scratch the glass and add a seed crystal

1. Presence of colored impurities 2. Desired compound oiling out 3. Premature crystal formation in gravity filter 4. Lack of crystal formation

When separating benzoic acid, naphthalene, and 3-nitroaniline, identify the solution used for each described purpose. 1. Extract aniline into the aqueous layer 2. Extract reconstituted benzoic acid out of the aqueous layer 3. Extract reconstituted 3-nitroaniline out of the aqueous layer 4. Extract benzoic acid into the aqueous layer 5. Reconstitute aniline from aqueous layer 6. Reconstitute benzoic acid from aqueous layer

1. 5% HCl solution 2. Dichloromethane 3. Dichloromethane 4. 5% NaOH solution 5. 6 M NaOH 6. 6 M HCl

Determine which base will work to deprotonate each compound in an acid/base extraction.

1. Only hydroxide 2. Neither hydroxide nor bicarbonate 3. Hydroxide or bicarbonate

When reacting yeast with sugars, what is the most prominent evidence that fermentation has occurred?

Formation of a gas

A cone-shaped tool with a porous plate inside above a long hollow stem, used to separate solids from liquids

Hirsch funnel

Experimental melting point is below literature value

Impure sample of multiple compounds

Wide melting point range

Impure sample of multiple compounds

If the SN2 reaction of an aromatic alcohol with an alkyl halide, like the synthesis of nerolin, is successful, what changes would be seen in the IR spectrum for the product compared to the starting material?

The addition of sp3 C-H bands in the product The disappearance of an O-H band from the starting material

A thin material placed in the funnel in order to collect the solid

filter paper

Identify items that can be used to control the boiling when heating liquid in a round bottom flask.

a stir bar and stir plate boiling chips or stones

Which layer should contain the carboxylic acid in a two-layer mixture of water and an organic solvent, like diethyl ether? You then add a base to form the corresponding carboxylate. Which layer should contain the carboxylate in a two-layer mixture of water and an organic solvent, like diethyl ether?

1. The organic layer 2. The aqueous layer The carboxylic acid is a neutral organic compound. Therefore, the carboxylic acid should be most soluble in the organic solvent. The related carboxylate is the deprotonated form, which has a negative charge. The charged species is more soluble in water and should appear in the aqueous layer.

What is the recommended order of measurements to report the most accurate melting point possible?

1. Use quick heating to estimate the melting point. 2. Use slow heating to carefully observe melting. 3. Use slow heating to confirm the careful measurement.

Identify the expected result of the iodine test with different carbohydrates. 1. Sucrose 2. Glycogen 3. Cellulose 4. Amylose

1. no reaction 2.red-purple soln. 3. ?? 4. blue-black soln.

Identify the type of sugar corresponding to each name. 1. Starch 2. Sucrose 3. Glucose 4. Fructose 5. Lactose

1. polyscacc 2.disacc 3. monosacc 4. monosacc 5. disacc

A solid sample is observed to melt between 42 and 52 ºC in a rapid melting point trial. Another melting point trial of the same solid is then carried out. In the second trial, the temperature is increased rapidly to 37.0 ºC, and then the rate of heating is decreased. The first drop of liquid in the sample appears at 46.7 ºC, the sample is completely liquid at 48.3 ºC, and the heating is stopped at 51.0 ºC. How should the approximate melting point be recorded? __________ How should the precise melting point be recorded? ____________

42-52 ºC.; 46.7-48.3 ºC.

Suppose you start with a 1.66 g sample of aspirin. After recrystallizing the sample, you have 1.32 g of aspirin. What is the percent recovery of aspirin in this recrystallization experiment?

79.5 %; Percent recovery compares the mass of aspirin after recrystallization to the mass of aspirin before recrystallization. % recovery=(mass of aspirin after recrystallization/mass of aspirin before recrystallization)×100 Therefore, the correct calculation of the recovered percentage of copper is % recovery=(1.32 g of aspirin1.66 g of aspirin)×

Suppose you are using distillation to separate cyclohexane and toluene. The boiling point of cyclohexane is ___ oC and the boiling point of toluene is _____oC. Therefore, the liquid collected first should be _________.

81; 111; cyclohexane

Where should the tip of the thermometer be placed in a microscale distillation set-up?

At or slightly below the side arm of the distillation head

Moves desired compound from one layer to another Often involves a reaction in one of the layers Leaves impurities in their starting layer

Extraction

Identify necessary precautions when carrying out a vacuum filtration with organic materials.

Inspect the glassware for cracks or chips prior to use. Clamp the filtration apparatus to a ring stand if it feels unstable.

Suppose you need to recrystallize compound B, which has a melting point of 75 oC and the solubility behavior shown in the table. Solvent Boiling point (oC) B Solubility at 25 oC B Solubility at BP Water 100Insoluble Soluble Methanol 65Insoluble Soluble Acetone 56Soluble Soluble Diethyl ether 35Soluble Soluble Which solvent should you use to recrystallize compound B?

Methanol; A recrystallization needs to dissolve the compound only near its boiling point. Also, the recrystallization should not melt the compound. Therefore, the best solvent is methanol. Both water and methanol dissolve the compound near their boiling points but not at room temperature, as desired. However, water's boiling point is above the compound melting point and the compound would oil out rather than crystallize.

Why is potassium hydroxide preferred over sodium hydroxide in organic reactions?

Potassium hydroxide is more soluble in organic alcohols.

Experimental melting point is close to literature value

Pure sample of a single compound

Narrow melting point range

Pure sample of a single compound

If crystal growth does not start on its own after the solution in the flask returns to room temperature, identify the best ways to promote this process.

Scratch the bottom of the flask gently with a stirring rod. Add a bit of solid as a seed crystal.

Before turning on the heat for a microscale distillation, what should you confirm about the set-up?

Secure connections at the joints Existence of some opening in the set-up Presence of boiling chip in the sample

Which property is the basis of the purification technique recrystallization?

Solubility

What is meant by the term bumping?

Sudden and uncontrolled boiling of liquid

Suppose you are performing an acid/base extraction. After one of the steps, you have collected a NaOH extract containing the pictured phenolate. Next, you add HCl to the layer. What are the products of the HCl addition?

The acid can donate a proton to the phenolate, forming the related phenol. The other product in the layer is the chloride ion left after the acid loses its proton. The general reaction is PhO−+HCl⟶PhOH+Cl−

Describe the complete role of the acid catalyst in the dehydration of an alcohol.

The acid protonates the hydroxyl group and then the conjugate base deprotonates an adjacent carbon.

Why does the dehydration of an alcohol more often use concentrated sulfuric acid, H2SO4 , as the acid catalyst rather than dilute hydrochloric acid, HCl ?

The additional water solvent from a dilute solution could reverse the dehydration reaction. The presence of the chloride ion could result in a competing substitution reaction.

If the dehydration reaction of an alcohol is successful, what changes would be seen in the IR spectrum for the product compared to the starting material?

The disappearance of an O-H band from the starting material The addition of a C-C double bond band in the product The disappearance of a C-O band from the starting material

When melting mixtures of compounds, what is the eutectic composition?

The mixture composition with the lowest melting point

What are the concerns presented by overheating a distillation to a dry flask?

The remaining solid residue might contain explosive peroxides. The empty glassware might heat quickly, igniting vapors from the distillation.

Which solvent should be used to wash the solid material collected from a filtration?

The same solvent as the liquid in the original mixture

Why might it be difficult to detect when a solid sample starts melting in a melting point apparatus?

The sample changes shape without starting to liquefy. The sample melts too quickly due to very little impurity. Some of the sample sublimes rather than melting.

Some carbohydrates are classified as reducing sugars due to their ability to reduce other reagents. What features of a carbohydrate usually indicate that it is a reducing sugar?

There is a hemiacetal in the ring form. There is an aldehyde in the chain form.

Moves impurities from one layer to another Leaves desired compound in its starting layer

Wash

Under what condition should fractional distillation be used instead of standard distillation for the separation of two liquids?

When the boiling points of the liquids are close

Many reflux procedures involve a required length of time for the reflux to occur.When should you start timing the reflux for the procedure?

When the reflux ring stabilizes in the condenser

Consider a mixed sample of 70% of compound Y and 30% of compound X in which Y melts at a higher temperature than X. In this sample, ____________. As heat is applied, starts to melt first, which is when __________________. Then, _____________ melts later.

X is an impurity in Y; compound X;melting is first observed; compound Y

Consider the SN2 reaction of an alcohol with an alkyl halide in the presence of base. The ___________ should be added to the alcohol first to ____________ the alcohol and allow it to attack the ____________.

base; deprotonate; alkyl halide

Aniline involves an amine, which is a ________ functional group. When an aqueous acid solution is added to an organic solution including aniline, the aniline appears in the __________ layer in its ___________ form. Then, a base is added to _____________ the aniline.

basic; aqueous; protonated; reconstitute

When working in the fume hood, it is important to make an effort to minimize ____________. Only keep items in the hood if they are being used for ____________. Do not _________ chemicals in the fume hood unless instructed to do so.

clutter; the current experiment; store

When using acids and bases, note that these substances are _____________. Make every effort to avoid contact with __________________. Be sure to wipe up any spills ___________.

corrosive; the skin and lab surfaces; immediately

Before using the flask, inspect it for _____________. Use ____________ for stability when suspending the flask on a ring stand. Never heat a flask that is _________.

cracks or imperfections; a clamp; closed

In the presence of acid and heat, ____________ will undergo a more effective dehydration reaction because it is a __________ alcohol and the ____________ in the intermediate of the mechanism will be more stable.

cyclohexanol; secondary; cation

After the filtration apparatus for an organic mixture is set up, begin the separation by ___________ the sample into the __________ of the filter paper. Wash the solid with cold solvent to help all liquid drain from the funnel. Gently stir the solid if needed, and continue to pull the vacuum for a few minutes in order _______________.

decanting; center; to dry the solid

When performing the acid-catalyzed dehydration of an alcohol, the yield of product can be increased by ________________ during the reaction. The dehydration is ____________, and removing the product from _________________ reduces the hydration reaction.

distilling off the product; reversible; the reaction flask

A container with a broad base, narrow opening, and a side arm, used to collect liquid

filter flask

Before assembling a distillation apparatus, lubricate the ground glass joints of each piece of glassware using __________. This helps seal the connection between two components. Once two components are fit together, use _______ to make the connections secure. Stabilize the complete distillation setup using a __________.

grease; clamps; ring stand

Identify heating apparatuses suitable for use with round bottom flasks.

heating mantle water bath oil bath

The dehydration of a secondary alcohol, like cyclohexanol, is a mechanism that occurs _____________. First, the alcohol is protonated to ___________________, creating ______________ intermediate. Then, a ______________ is removed, moving the electrons from that bond to make a _____________ bond.

in two steps; leave as a water molecule; a cation; hydrogen ion; carbon-carbon double

At the melting point, the solid form of a substance _______________ the liquid form of the substance.

is in equilibrium with

In order to dissolve a chemical sample in a recrystallization solvent, add the room-temperature solvent ___________ in an Erlenmeyer flask on a hot plate. Turn on the heat, starting at __________________. Using a _______, add additional solvent from a second container on the heat source. Swirl the sample flask after each addition, and try to add _______________ in order to dissolve the solid.

just until it covers the sample; a low setting and increasing gradually; pipet; as little solvent as possible

Seliwanoff's test shows the presence of A positive Seliwanoff's test appears as A negative Seliwanoff's test appears as

ketoses a red soln. a light pink soln.

After a recrystallization, a pure substance will ideally appear as a network of _______________. If this is not the case, it may be worthwhile to reheat the flask and allow the contents to cool more _________________.

large crystals; slowly

Distillation is the separation of multiple ________ components based on their different ____________. As the mixture is heated and the first component ________, its ________ form travels through the distillation set-up and __________ into a different container.

liquid; boiling points; boils; vapor; condenses

Distillation is the separation of multiple _______________ components based on their different ____________. As the mixture is heated and the first component ________, its __________ form travels through the distillation set-up and ___________ into a different container.

liquid; boiling points; boils; vapor; condenses

When it is time to end a reflux, first ______________ and then turn off the heat. __________________________________ until the system has cooled.

lower the heat source; Leave the condenser water on

To insert a thermometer into an adapter, use ___________ to prepare the thermometer. Then, hold the thermometer ___________ the adapter and _________ the thermometer into the adapter.

mineral oil; close to; slowly turn

Fructose is an example of a ketohexose. The -hexose part of the name indicates that fructose is a _________ that contains ___ carbons. The keto- part of the name indicates that fructose contains _________ functional group. Fructose can combine with glucose to form sucrose. Therefore, sucrose is a ____________.

monosacc; 6; a ketone; disacc

To prepare a sample in a capillary tube for a melting point determination, gently tap the tube into the sample with the ______ end of the tube down. Continue tapping until the sample ____________________. Then, with the _________ end of the tube down, tap the sample down slowly or _____________________________ to move the sample down faster. Finally, make sure that you can see __________ in the magnifier when placed in the melting point apparatus before turning on the heat.

open; is a couple millimeters high; closed; drop the tube into a longer tube; some or all the solid

Benedict's test shows the presence of A positive Benedict's test appears as A negative Benedict's test appears as

reducing sugars a reddish precipitate a blue solution

A flexible piece, typically either circular or cone-shaped, used to seal the opening between the funnel and the flask.

rubber adaptor

Suppose you need to assess the purity of a sample that has a reported experimental melting point of 105-106 oC. The _________________ indicates purity but we need to know and compare the __________________________ to confirm it. Therefore, you ___________ conclude that the sample is pure.

small melting point range; expected pure melting point; cannot

A portion of the setup consisting of a funnel, tubing, and an adaptor, used to keep the liquids from sink and the filtration apparatus separate

solvent trap