labos

What should you try first if a very small fire starts on your desk?

If a fire starts in a beaker or flask, cover the vessel with a flat object to cut of the supply of air.

You have a mixture of 2-chlorobenzoic acid (pKa 2.92) and 4-Bromophenol (pKa 10.2) dissolved in ether. You will need the following information: The pKa of HCl is -7; pKa of carbonic acid (H2CO3) is 6.52 and the pKa of water is 15. Which species do you use to separate the mixture? Which species will remain in the ether layer?

sodium bicarbonate 4-Bromophenol

Rank standards from Plate from Least to Most Polar:

aspirin, acetaminophen, caffeine

An amount of the dibenzalacetone crystals formed are recrystallized using 70:30 ethanol/water solution. What are the next 2 immediately sequential actions AFTER a boiling stick is added to the test tube once a few drops of solvent is added to the solid? (Don't skip steps)

1). Heating solution with boiling stick while adding hot solvent till solid is dissolved 2). Remove boiling stick

If you wish to form product B, to which starting carbonyl would you add a strong base such as LDA in order to form the enolate? Which carbonyl would you then add slowly to the enolate of the first carbonyl?

1-(1-methylcyclopentyl)ethanone propiophenone

In theory, which alkyl halides that you are using in the experiment undergo SN2 reactions? Which alkyl halides that you are using in the experiment undergo SN1 reactions? Which alkyl halides that you are using in the experiment don't undergo SN2 or SN1 or both reactions?

1-chlorobutane, 1-bromobutane, 2-chlorobutane, 2-bromobutane 2-chloro-2-methylpropane, 2-chlorobutane, 2-bromobutane Bromobenzene

In order to minimize forming a mixture of products in the reaction in the question above, which reactant would you use an excess of? Why?

2,2-dimethylpropanal It has no alpha hydrogens

The fast determination of the first sample of your unknown shows the unknown melting around 112∘∘C. At what temperature should you slow down the rate of heating to 1∘∘C/min? You have to pick two standards that could be your unknown because you don't know if thermometer calibration is an issue - the first standard MUST be listed alphabetically before the second standard : If your unknown is indeed the alphabetically second standard that you chose, what would happen to the mixed melting point of your unknown +this standard? Based on the result above, what would happen to the mixed melting point of your unknown + the alphabetically first unknown that you picked? What is the identity of your unknown?

92 degrees acetanilide, m-toluic acid melting point stays the same melting point goes down m-toluic acid

Recrystallization Prelab Question: Where do the following items need to be disposed after carrying out the melting point experiment?

Glass pipette after use - Sharps container Disposable Test tube - Broken glass container Used filter paper - Regular Trash Ethanol filtrate - Solvent/liquid waste

Why would boiling stones not be able to control the bumping of liquids in vacuum distillation as they are able to for simple and fractional distillations?

Boiling stones can't activate in a vacuumed system and so it can't absorb or trap liquids to control bumping.

Where should you dispose of disposable glassware?

Broken glass container

Besides a large spot and the TLC sample being too concentrated, what two other factors can cause the developed spots to appear as a streak?

Certain solvents, too many components in solvents

What should you always do before lighting a match in the lab?

Check for volatile solvents

In the citric acid cycle when an aldol addition occurs in a biological system, how do the amino acids contained in the Citrate Synthase enzyme help facilitate the reaction?

Citrate Synthase is the enzyme that catalyzes the reaction. The amino acids deprotonate the alpha carbon on Acetyl CoA, which acts as the nucleophile. Amino acids also protonate the oxygen attached to the carbonyl carbon (that's attacked by the nucleophile). Deprotonating and protonating facilitate the reaction because amino acids play the role of hydroxide and water in the regular reaction.

What can one do to obtain a second crop of crystals after initial crystals have been collected? What is the drawback of this method?

Collect filtrate and washings, evaporate until saturated

In vacuum distillation, how you do ensure that the liquid does not boil too suddenly upon reduction of pressure?

Heat the flask after the system is vacuumed to the right pressure.

What should you always wear over your eyes while in the lab even if your wear glasses?

Face-fitting goggles

What should you always do if you have to leave the lab or feel unwell or see a classmate who is unwell while in the midst of carrying out an experiment?

Inform you lab instructor.

Since boiling stones cannot be used to control the bumping of liquids in vacuum distillation, other methods are used. What is specifically done with glass wool (one of the implements used to control bumping) when small quantities of material are being distilled via vacuum distillation?

Introduce enough glass wool into the flask to fill part of the space above the liquid.

Let's consider that ethyl acetate is the ideal solvent for this TLC experiment. What might have happened to the spots if you had used acetone as the eluent instead of ethyl acetate. Why?

Spots move towards top of TLC plate acetone more polar, overcomes attractions of sample to adsorbent better

What aspect of water makes it favorable to use in steam distillation?

Its low molecular weight

Where do the following items need to be disposed of when carrying out the experiment:

Melting Point Capillary - Sharps Container Disposable Test Tube - Broken Glass Container Pipette- Sharps Container Excess solvent - Solvent/liquid waste Used paper towels - Regular trash

Prelab Question: Where do the following items need to be disposed after carrying out the melting point experiment?

Melting Point Capillary after use - Sharps container Disposable Test tube - Broken glass container Used weighing paper - Regular Trash Leftover solid organic compound - Solid chemical waste

What species (among HCl, NaOH and NaHCO3) could you use to separate the components of Mixture C? What species would exist in the aqueous layer AFTER the extraction?

NaHCO3 Sodium salt of 4-nitrobenzoic acid

What is the order of reagents that were added to the test tube used to carry out the synthesis of dibenzalacetone?

NaOH benzaldehyde acetone in ethanol

Are contact lenses ever permitted in the Chemistry laboratory in Rutgers?

No

What is the vapor pressure of a sugar solution dependent on?

Number of water molecules per given volume

List two movements molecules of a solid may undergo as they are heated before the solid melts.

Rotation + vibration

What device should you use if concentrated acid or base spills on your clothing?

Safety showers

What heat source should you use to heat flammable organic solvents?

Sand bath

Where should you dispose of capillary tubes and pipettes?

Sharps container

What should you do if your clothing catches fire?

Shove person under a safety shower if there is one nearby. If not, push the person to the floor and roll him/her until the flames extinguish.

What is the purpose of having very small bores on the spotters?

So that once liquid is drawn into them, it will not flow out to form a drop

How should you dispose of excess organic solvents?

Solid/liquid waste

In column chromatography (microscale), after loading it with solvent and adsorbent and prior to loading the sample, what level should you allow the solvent to drop to? Why should you not allow the sample to run dry and what is the consequence if you had allowed it to do so?

Solvent should drop to the top of the packing. The sample shouldn't be allowed to run dry because it would allow air bubbles and channel formation to surface. This would allow for poor separation.

Let's consider that ethyl acetate is the ideal solvent for this TLC experiment. What might have happened to the spots if you had used t-butyl methyl ether as the eluent instead of ethyl acetate. Why?

Spots remain towards bottom of TLC plate t-butymethyl ether less polar, cannot overcome attractions of sample to adsorbent

What actions should you take if the fire alarm goes off?

Stop all experimental work and leave all chemicals/equipment in the lab. Follow instructions of lab instructor and head for an exit and assemble outside the building to the area you were instructed to go to by the lab instructor as quickly as possible.

In an ester, what feature further increases the electrophilicity of the carbonyl carbon?

The -OR group attached to the carbonyl group increases its electrophilicity.

Why do the NaCl plates used for IR need to be handled with care? What precautions need to be taken when handling them?

The NaCl plates need to be handled with care because they can easily break. It is susceptible to moisture and so it needs to be kept away from aqueous solutions and moisture. The plates are handled by the edges.

4-Nitrobenzoic acid has a pKa of 3.41. p-Cresol has a pKa of 10.26. 3-Fluorophenol has a pKa of 8.40. You will need the following information: The pKa of HCl is -7; pKa of carbonic acid (H2CO3) is 6.52 and the pKa of water is 15. Mixture A is a mixture of p-cresol and 3-fluorophenol. Mixture B is a mixture of 4-nitrobenzoic acid and p-cresol. Mixture C is a mixture of 4-ntirobenzoic acid and 3-fluorophenol. All mixtures are dissolved in methylene chloride. Why would reacting Mixture A with an aqueous solution of NaHCO3 (sodium bicarbonate) NOT separate one substance from the other?

The acidity of carbonic acid is stronger than both components so neither will be extracted into the aqueous layer

Why would reacting Mixture B with an aqueous solution of NaOH (sodium hydroxide) NOT separate one substance from the other?

The acidity of water is weaker than both components so both will be extracted into the aqueous layer

Define steric hindrance in a nucleophilic substitution reaction.

The ease with which the nucleophile can come within bonding distance of the alkyl halide

What character of the actual elements (aluminum, silicon, oxygen) present in alumina and silica cause the stationary phase to be very polar?

The electropositive character of aluminum and silicon and the electronegative character of the oxygen.

What are the intensity of the IR absorption bands proportional to?

The intensity of the IR absorption bands is proportional to the change in a dipole moment of a bond when it stretches.

When comparing 2 hydrocarbons, why would the larger, higher molecular weight molecule have a higher melting point?

The larger hydrocarbon has a higher melting point because it possesses more Van Der Waal forces. Although they're weakest kind of forces, they increase as the molecular size increases.

In the solvent pair experiment that is being carried out with the solid that is being recrystallized, why do you NOT have to worry about sudden vigorous boiling of crystal solution when you add the second solvent to the solution?

The second solvent will have a higher boiling point than the first one and the temperature of the solution has to be lowered before adding the second one.

The reason the TLC could not be visualized by UV is because: The reagents 1) Oxone, acetone 2) H3O+ forms the more polar diol - what is the product?

The spots were not concentrated enough trans-diol

Define the term separation it relates to general chromatography.

The term separation as it relates to general chromatography refers to the components that are distributed between 2 phases, stationary and mobile.

Why are glass, quartz and plastics not used as IR sample holders?

They're not used because they're opaque to IR radiation and will not absorb it. The sample material must be transparent.

Aldol Condensation Title with reference: Statement of Purpose: Chemical Hazards and Precautions:

Title with reference: Aldol Condensation, Organic Chemistry Lab pg 485-486 Statement of Purpose: Synthesis of Dibenzalacetone via aldol condensation

Distillation Title with reference: Statement of Purpose: Chemical Hazards and Precautions:

Title with reference: Distillation, Organic chemistry laboratory, Pg 92-95 Statement of Purpose: 1). Learning the technique of distillation 2). Comparing simple and fractional distillation of cyclohexane/toluene mixture Chemical Hazards and Precautions: Cyclohexane - flammable, causes eye and skin irritation Toluene - flammable, causes eye and skin irritation

Nucleophilic substitution Title with reference: Statement of Purpose: Chemical Hazards and Precautions:

Title with reference: Nucleophilic Substitution, Organic Chemistry lab pg 323-325 Statement of Purpose: To compare SN1 and SN2 reactions of various alkyl halides Chemical Hazards and Precautions: 1-chlorobutane - cause eye, skin, and digestive refractive irritation 1-bromobutane - cause eye, skin, and digestive refractive irritation 2-chlorobutane - cause eye, skin, and digestive refractive irritation 2-bromobutane - cause eye, skin irritation 2-chloro-2-methylpropane - cause eye, skin, and digestive refractive irritation Bromobenzene - cause eye, skin irritation Acetone - cause eye, skin irritation Sodium Iodide - cause eye, skin irritation Ethanol - cause eye, skin irritation Silver Nitrate - cause eye, skin burning

TLC Title with reference: Statement of Purpose: Chemical Hazards and Precautions:

Title with reference: Thin-Layer Chromatography, Chemistry 311 handout Statement of Purpose: 1). Learn technique of TLC 2). To determine the identify of the unknown compound Chemical Hazards and Precautions: Acetaminophen - overdose can lead to liver injury/failure Aspirin - causes eye, skin, and respiratory tract irritation Caffeine - may cause eye and skin irritation Ethanol - causes respiratory tract and eye irritation Methylene Chloride - may cause eye and skin irritation Ethyl Acetate - may cause eye and skin irritation Personal precautions when experimenting with these chemicals is to use wear goggles, gloves, and stay under the fume hood.

Recrystallization Title with reference: Statement of Purpose: Chemical Hazards and Precautions:

Title: Crystallization of a solid from water and from a solvent pair (ethanol/water), Organic Chemistry Laboratory 311 pg 81 Statement of Purpose: 1). Learn techniques of recrystallization and to compare the two methods of crystallizing whicheer solid you are assigned. 2). Calculate % recovery for the postlab Chemical Hazards and Precautions: Acetanilide - may cause eye, skin, and respiratory tract irritation Salicylic Acid - may cause eye, skin, and respiratory tract irritation Ethanol - may cause eye, skin, and respiratory tract irritation

Melting Point Title with reference: Statement of Purpose: Chemical Hazards and Precautions:

Title: Melting Point, Organic chemistry laboratory 311 pg. 54 Statement of Purpose: 1). Learning the techniques for identifying melting points. 2). Determining the eutectic range of a mixture of cinnamic acid and urea. 3). Identifying unknown substances based on its melting points. Chemical Hazards and Precautions: 1). Cinnamic Acid - causes eye, skin, and respiratory tract irritation 2). Urea - causes eye, skin, and respiratory tract irritation 3). Acetanilide - causes eye, skin, and respiratory tract irritation 4). Benzoic Acid - causes eye, skin, and respiratory tract irritation 5). Benzophenone - causes eye, skin, and respiratory tract irritation 6). 4-Nitrotoulene - Toxic if inhaled and/or swallowed. 7). M-Toluic Acid - causes eye damage/irritation 8). R,S-Mandelic Acid - causes eye and skin irritation 9). Salicylic Acid - causes eye, skin, and respiratory tract irritation 10). 1,2-benzanthracene - Is a carcinogen. May cause cancer if exposed for long period of time

Where should you work when transferring irritating or poisonous substances?

Under a good exhaust hood.

What is the character of the vapor after each condensation-vaporization cycle in a fractional distillation of a mixture?

Vapor is richer in the more volatile fraction

What specifically causes the vaporization of the lower boiling liquid on the packing in a fractional distillation?

Vaporization is caused by the heat released during condensing of the higher boiling vapor. The large surface area of the packing allows for vapors coming up the column and liquid coming down the column to interact.

Other than solubility of sample in the solvent, what is the criteria for the solvent (other than cheap and nontoxic) used for preparing the sample that impacts the experiment and why would this criteria be important in the spotting phase if you have to make repeated applications of the sample?

Volatile because it has to be able to evaporate from the sample which leaves only the sample on the TLC plate.

What should you do if a chemical gets in your eyes?

Wash eyes at the eyewash station until medical assistance arrives.

What should you do if concentrated acid or base spills on your hands and arms?

Wash the applicable areas with lots of water, using the safety shower until medical assistance arrives.

Why would water not be used to elute a column (besides it polarity) in column chromatography?

Water can dissolve some of the silica gel which would harm the stationary phase.

In what case would column chromatography be used to purify a desired compound because techniques like recrystallization, extraction and distillation are not adequate to do so?

When the impurities all have similar properties and are closely related in structure.

Explain the adiabatic process as it specifically pertains to a fractional distillation.

When the vapor coming up the column interacts with the liquid coming down the column in the packed bed, the energy released from the vapor is absorbed by the liquid with no gain or loss of heat to the environment.

You come across a white solid and take its melting point and find it to be 82-85°C. You decide to identify it. If the thermometer is calibrated, compounds of what general melting point range can you automatically eliminate and why? (For the general melting point range, indicate above or below a certain melting point or in between melting ranges. Don't provide specific compounds as examples)

You can automatically eliminated compounds whose melting points are lower than 85 deg C because if you're mixing a quantity of the unknown with a known compound (melting point < 85) and the combined melting point stays the same, then your unknown compound is your known compound. If the combined melting point goes down, then your unknown isn't the same as your known compound. Impurities in mixtures lower the combined melting points.

What device should you use immediately if a fire (except a very tiny one) starts near you?

You should use a carbon dioxide or dry chemical fire extinguisher to put out the fire. Report the incident so the extinguisher can be refilled.

In the synthesis of isobutyl propionate (shown on pg. 521), excess propanoic acid is used in the reaction. a) What purpose does the excess acid serve? b) What does this indicate with regards to the relative costs of the two starting materials in this synthesis?

a). Serves to drive the equilibrium reaction toward formation of the product b). This indicates that the acid is cheaper than the isobutyl propionate

When running a spectrum of a neat liquid, what are problems that may arise when: a) using a low-viscosity liquid? b) using a viscous liquid?

a). The spectrum will appear thin, allowing the short path lengths to produce peaks that are hard to interpret. b). The spectrum will appear thick, allowing the short path lengths to produce peaks that are too intense.

a) Why would the presence of the side product benzalacetone be minimized? b) Why would the presence of the side product 4-hydroxy-4-methyl-2-pentanone be minimized?

a). Using a reactant with no alpha-H which is benzaldehyde allows for only one carbonyl to form an enolate which is acetone. We use an excess amount of benzaldehyde because benzalacetone now has an alpha-H and it reacts with another benzaldehyde to form dibenzalacetone thus minimizing benzalacetone. b). Benzaldehyde is more reactive than acetone. Acetone is a ketone and ketones are less susceptible to nucleophilic attack at carbonyl carbons than aldehydes.

You have a 1:1 mixture of 2,2,4-trimethylpentane (boiling point: 99∘C) and methoxybenzene (boiling point: 154∘C) that you wish to separate. a) What common criteria would this mixture have to satisfy in order to be separated by either simple or fractional distillation? homogeneous b) What kind of distillation (between simple and fractional) would be efficient for this mixture? c) Why would the distillation type chosen in question b) be ideal for this mixture?

homogeneous fractional boiling point difference and composition

You are given a unknown white solid to recrystallize in lab. The white solid could be Compound A (melting point 110-112°C), Compound B (melting point 165-166°C) or Compound C (melting point 156-157°C). Compound A, B and C are significantly soluble in butyl acetate (bp: 126°C), even at room temperature and not very soluble in water (bp: 100°C) or n-butanol (bp: 125°C) (difference in solubility of solid in water and ethanol is not significant) . Butyl acetate is miscible with n-butanol but not with water. a) If you decide to use butyl acetate (must use this solvent) and choose between n-butanol and water as the solvent pair for the unknown white solid, describe which solvent you would heat up and dissolve the solid in initially and which solvent you would add second and at what point would you stop adding the second solvent b) f you could use butyl acetate as the single recrystallization solvent for the solid, which compound might have a problem of oiling out?

hot butyl acetate n-butanol first signs of cloudiness A

The washing step of recrystallization removes which category of impurities?

on the surface of the solid

The crystallization step of recrystallization removes which category of impurities?

within the crystal lattice