Orgo Lab final
In a micro scale distillation, the rate of distillation should be about one drop per ___ to ___ seconds
20 to 30
An unknown alcohol, aldehyde, or ketone produced a reddish-orange precipitate upon reaction with 2,4-dinitrophenylhydrazine, a negative Schiff test, and a positive iodoform test. Which of the following compounds is the unknown most likely to be? A. 4-methyliso-butyrophenone B. 1-(2-chlorophenyl)propanone C. 4-methoxybenzaldehyde D. 3-fluoroacetophenone
3-fluoroacetophenone
An unknown alcohol, aldehyde, or ketone produced a reddish-orange precipitate upon reaction with 2,4-dinitrophenylhydrazine, a negative Schiff test, and a negative iodoform test. Which of the following compounds is the unknown most likely to be? A. 3-bromobenzaldehyde B. 4-methyliso-butyrophenone C. (4-methoxyphenyl)ethanal D. 1-(4-methoxyphenyl)propanone
4-methyliso-butyrophenone
A sterically unhindered alcohol and a sterically unhindered carboxylic acid are allowed to react in the presence of sulfuric acid. If a 1:1 mole ratio of carboxylic acid to alcohol is used, what is the maximum % yield of ester that may be isolated?
70%
The catalyst used in the dehydration of cyclohexanol is A. 15% phosphoric acid B. 85% phosphoric acid C. concentrated sulfuric acid D. phosphorus tribromide
85% phosphoric acid
A solid sample melted at 81.0-85.5°C. The compound was one of four possibilities, having the mp's shown below. Which was it most likely to be? A. 85.5 B. 81.0 C. 83.0 D. 87.0
87.0
The melting point of a sample of compound X was found to be 173 - 177 ° C. Compound X was one of four possible compounds having melting points of 173, 175, 177, and 179 °C. Which was it most likely to be?
179
In this lab a melting range of ____ ° C indicates that a compound is relatively pure.
2
In a TLC analysis, if the Rf of a compound was found to be too large, a ________(spotting or development?) solvent having a ______(lower or higher?) polarity should be chosen.
Development, lower
A sample of naphthalene was mixed with water and tert-butyl methyl ether. The naphthalene dissolved mostly in the ____(water or ether?) layer. The ether layer was the ____(upper or lower?) layer.
Ether, upper
In gc, if five peaks are observed it can be assumed that there are five components in the sample. A. True B. False
False
The solubility of substance A in four different solvents at low temperature and high temperature are given below. Which solvent is the best for recrystallizing substance A ? Solubility Low T High T toluene 51 g/ml 86 g/ml water 3 g/ml 11 g/ml hexane 7 g/ml 145 g/ml acetone 120 g/ml 146 g/ml
Hexane
Which of the following organic solvents would be suitable for use in the extraction of an aqueous solution? A. acetone B. hexane C. methanol D. ethanol
Hexane
In this experiment a comparison of simple vs fractional distillation is done by comparing plots of ____ vs ___ .
temperature vs volume
Name the alcohol and carboxylic acid (in that order) used to make the ester, n-propyl acetate
-1-propanol -acetic acid
The following questions are for the dehydration of cyclohexanol. Cyclohexanol MW: 100.2 g/mol Cycohexene MW: 82.1 g/mol Starting with 1.60 g of cyclohexanol, what is the theoretical yield of cyclohexene in mol (do not add the units to these answers)?_____ mol What is the theoretical yield in g?___ The amount of product obtained after the final distillation is 0.983. Assuming that the distillate is pure cyclohexene, what is the % yield of product?____ If gas chromatography of the distillate showed that the purity of product was 0.780, what is the % yield of pure cyclohexene?____
-1.60E-2 -1.31 -77% -58.5%
Note that carboxylic acid is used in slight excess (mol alcohol + 0.001 mol). To synthesize 0.022 mol of 3-methylbutyl butanoate, _____ grams, or ____ mL of 3-methyl-1-butanol and _____ grams, or _____ mL of butanoic acid are needed. MW of 3-methyl-1-butanol = 88.2 g/mol density of 3-methyl-1-butanol = 0.809 g/mL MW of butanoic acid = 88.1 g/mol density of butanoic acid = 0.958 g/mL
-1.94 g or 2.4 mL -2.03 g or 2.12 mL grams = MW x mol mL = grams/density
Hydrolysis of 0.018 mol of the fat, tristearin, yields how many grams of stearic acid (MW = 228)?
-15.4 grams -One mole of fat yields three moles of carboxylic acid, so grams of carboxylic acid = MW(acid)*mol(fat)*3, or specifically for this case grams of acid = 228*3*0.018 = 15.4
A sterically unhindered alcohol and a sterically unhindered carboxylic acid are allowed to react in the presence of sulfuric acid. If a 3:1 or 1:3 mole ratio of carboxylic acid to alcohol is used, what is the maximum % yield of ester that may be isolated?
-90%
Which of the following would be considered to be physical properties? (check all correct answers) A. Acidity of 2-chlorobenzoic acid. B. Melting point of cholesterol. C. Boiling point of 2-methylnonane. D. Solubility of caffeine in dichloromethane. E. Rate of the SN2 reaction of 1-bromobutane and potassium tert-butoxide.
-Boiling point of 2-methylnonane -Melting point of cholesterol -Solubility of caffeine in dichloromethane
Which of the following would be considered to be chemical properties? (check all correct answers) A. Acidity of 2-chlorobenzoic acid. B. Solubility of caffeine in dichloromethane. C. Boiling point of 2-methylnonane. D. Melting point of cholesterol. E. Rate of the SN2 reaction of 1-bromobutane and potassium tert-butoxide.
-Rate of the SN2 reaction of 1-bromobutane and potassium tert-butoxide. -Acidity of 2-chlorobenzoic acid.
In a distillation what two pieces of information can be obtained? A. The melting point of each component. B. The ratio of the amounts of the components in the original mixture. C. The density of each component. D. The heat of vaporization of each component. E. The boiling point of each component.
-The ratio of the amounts of the components in the original mixture -The boiling point of each component.
For the following molecule, the hydrogens having the largest chemical shift are labelled (a, b, c, or d?) Cl-CH2-CH2-CH2-CH3 a b c d
-a The hydrogens closest to the chlorine will have the largest chemical shift (furthest to the left in the spectrum).
Select the four characteristics of a proton NMR spectrum that are used to help interpret the spectrum. A. height of signals B. multiplicity of signals C. number of signals D. positions of absorption E. area of signals F. width of signals
-area of signals -positions of absorption -number of signals -multiplicity of signals
In gc, retention times and thus peak separation is determined by A. column length. B. carrier gas flow rate. C. column packing material. D. column temperature. E. All of the Above
-column length. -column temperature. -column packing material. -carrier gas flow rate.
In the permanganate test, the presence of an alkene group is indicated by A. a color change from reddish-orange to colorless. B. a color change from colorless to purple. C. a color change from purple to colorless. D. dibromide formation. E. formation of a brown precipitate.
-formation of a brown precipitate. -a color change from purple to colorless.
In the following molecule, the hydrogens labelled "d" will be split into how many peaks? Cl-CH2-CH2-CH2-CH3 a b c d A. seven B. three C. four D. five
-three -The hydrogens labelled "d" have two close neighbors (those labelled "c"). These two neighbors will split the "d" hydrogens into n + 1 peaks, where n = the number of neighbors (n + 1 = 2 + 1 = 3 peaks, or a triplet). The other hydrogens labelled "a" and "b" are too far away from the "d" hydrogens to affect them noticeably.
Another name for a fat is A. cholesterol. B. triglyceride. C. glycerol D. the sodium salt of a carboxylic acid
-triglyceride
In your experimental set-up, to maximize the yield of ester A. water is allowed to evaporate. B. water is removed with sulfuric acid. C. water is trapped in a side-arm. D. ester is trapped in a side-arm.
-water is trapped in a side-arm.
The fat, tripalmitin, when hydrolyzed with aqueous NaOH followed by acidification with HCl yields glycerol and palmitic acid. If 0.009 mol of tripalmitin is hydrolyzed, what is the theoretical yield of palmitic acid in moles?
.027 mol
If 0.029 mol of cyclohexanol reacts with 0.014 mol of 85% phosphoric acid, the theoretical yield of cyclohexene is ____ mol.
0.029 In this reaction, the phosphoric acid is a catalyst, and its amount affects only the rate at which the reaction occurs. It does not enter into the overall stoichiometry of the reaction. The theoretical yield of cyclohexene is determined solely by the amount of cyclohexanol used. By looking at the balanced reaction it is seen that 1 molecule (or 1 mole) of cyclohexanol produces 1 molecule (or 1 mole) of cyclohexene. The number of moles of starting alcohol therefore determines the theoretical amount of alkene that can be produced.
In a TLC analysis, if the solvent was observed to travel 10.0 cm and the spot was observed to travel 2.00 cm, what is the Rf for that spot?
0.200
In a melting point determination, the heating rate as the solid is melting should be ___ ° C per minute.
1
Give the three basic steps in TLC in the order in which they are done.
1. Spotting 2. Development 3. Visualization
A mixture of benzoic acid and naphthalene was dissolved in tert-butyl methyl ether and the resulting solution was extracted with aqueous sodium bicarbonate. The major organic species (excluding solvent) that is present in the lower layer is
Benzoic acid reacts with sodium bicarbonate to produce the sodium salt of benzoic acid (sodium benzoate). Although benzoic acid is more soluble in ether than in water, the salt of benzoic acid, being ionic and very polar, is more soluble in water than in ether. The denser lower water layer will thus contain the sodium benzoate. The upper ether layer will contain the naphthalene.
A mixture of benzoic acid and naphthalene was dissolved in tert-butyl methyl ether and the resulting solution was extracted with aqueous sodium bicarbonate. The major organic species (excluding solvent) that is present in the upper layer is
Benzoic acid reacts with sodium bicarbonate to produce the sodium salt of benzoic acid (sodium benzoate). Although benzoic acid is more soluble in ether than in water, the salt of benzoic acid, being ionic and very polar, is more soluble in water than in ether. The denser lower water layer will thus contain the sodium benzoate. The upper ether layer will contain the naphthalene.
A mixture of benzoic acid and naphthalene was dissolved in tert-butyl methyl ether and the resulting solution was extracted with aqueous sodium bicarbonate. The lower layer was separated and to it was added concentrated hydrochloric acid, upon which a white precipitate formed. What was the structure of the precipitate?
Benzoic acid reacts with sodium bicarbonate to produce the sodium salt of benzoic acid (sodium benzoate). Although benzoic acid is more soluble in ether than in water, the salt of benzoic acid, being ionic and very polar, is more soluble in water than in ether. The denser lower water layer will thus contain the sodium benzoate. Upon separating the lower layer and acidifying it with HCl, benzoic acid is regenerated, and because it has a low solubility in water, it precipitates out.
In a distillation the correct position of the thermometer is
In a distillation, to accurately measure the boiling point (bp) of the liquid being distilled, correct thermometer position is essential. The exiting vapors must immerse the mercury bulb completely. This is accomplished by placing the top of the mercury bulb at the same height as the bottom of the exit tube on the distilling head. Placing the thermometer too low will result in a temperature reading that is too high - the mercury bulb is immersed in boiling vapors that contain not only the material distilling but also higher-boiling material. If the thermometer is placed too high, the reading will be low because insufficient vapor is passing over the mercury bulb.
Two obvious structural features that may affect the solubility of a compound are A. its refractive index. B. its polarity. C. its ability to react with hydrogen. D. its inner electron configuration. E. its ability to form hydrogen bonds.
Its polarity Its ability to form hydrogen bonds
The three general types of impurities that may contaminate a solid sample are A. colored impurities. B. semi-soluble impurities. C. phenolic impurities. D. insoluble impurities. E. soluble impurities.
Soluble impurities Colored Impurities Insoluble impurities
Decaffeinating coffee or tea represents the following type of extraction: A. solid into a solvent B. solvent into a solid C. solid into a solid D. solution into another solvent
Solution into another solvent
After removing the crystallization solvent from the crystals, the crystals are rinsed with fresh solvent to remove impurities clinging to the surface of the crystals. Which statement is most correct? A. The amount of rinse solvent does not matter as long as it is ice-cold. B. The crystals should be rinsed with a minimum amount of warm solvent. C. The temperature of the rinse solvent does not matter as long as a minimal amount is used. D. The crystals should be rinsed with a minimum amount of ice-cold solvent.
The crystals should be rinsed with a minimum amount of ice-cold solvent.
Melting points can provide the following information about a sample. (Select all correct answers) A. The heat of formation of the substance. B. The functional groups present in the compound. C. The crystal structure. D. The identity. E. The purity.
The identity and the purity
Thin layer chromatography can be used to help determine (select all correct answers) A. the identity of a compound. B. the number of components in a mixture. C. the melting point of a compound. D. the density of a compound. E. the purity of a compound. F. the boiling point of a compound.
The identity of a compound. The number of components in a mixture. The purity of a compound.
If a second melting point determination must be taken for a sample, it is necessary to use a fresh sample and not the one that has already been used. Why? A. The crystal structure may have changed. B. A less pure sample may have been used the first time. C. The sample may have decomposed slightly. D. The sample will be drier after it has been left for a longer time.
The sample may have decomposed slightly.
After development and visualization of a TLC plate, four spots were observed. What can be concluded about the number of components in the original mixture? A. There are at least four components in the mixture. B. No conclusion can be made. C. There are more than four components in the mixture. D. There are four components in the mixture.
There are at least four components in the mixture.
A TLC analysis was run on an unknown mixture. After visualization by two methods, three spots were observed. What can be concluded? A. Six components are present in the mixture. B. There are three components in the mixture. C. No conclusion may be drawn. D. There are at least three components in the mixture.
There are at least three components in the mixture.
Solubility tests were carried out on an unknown solid and the following results were obtained: solvent cold hot water high high ethanol high high hexane low low toluene low high Which solvent would be the most suitable crystallization solvent A. either ethanol or water B. toluene C. ethanol D. hexane E. water
Toluene A suitable crystallization solvent is one in which the solid has a low solubility in cold solvent and a high solubility in hot solvent.
For a 2,4-dinitrophenylhydrazone, a reddish-orange color indicates the presence of A. an unconjugated carbonyl group. B. a methyl group one bond from the carbonyl. C. a double bond anywhere in the molecule. D. a conjugated aldehyde or ketone.
a conjugated aldehyde or ketone.
An unknown which was either an alcohol, an aldehyde, or a ketone produced a reddish-orange precipitate upon reaction with 2,4-dinitrophenylhydrazine, gave a positive Schiff test, and a negative iodoform test. It can be concluded that the unknown is A. an alcohol. B. a conjugated methyl ketone. C. a conjugated methyl aldehyde. D. a conjugated aldehyde. E. an unconjugated aldehyde.
a conjugated aldehyde.
In a TLC analysis if the Rf's of the spots are too small, A. a spotting solvent of higher polarity should be used. B. a development solvent of lower polarity should be used. C. a different method of visualization should be used. D. a spotting solvent of lower polarity should be used. E. a development solvent of higher polarity should be used.
a development solvent of higher polarity should be used.
In the iodoform test, formation of a yellow precipitate indicates the presence of A. an aldehyde group one bond away from another multiple bond. B. a nonconjugated aldehyde or ketone. C. a methyl group anywhere in the molecule. D. a methyl group directly attached to the carbonyl of an aldehyde or ketone.
a methyl group directly attached to the carbonyl of an aldehyde or ketone.
An unknown which is an alcohol, an aldehyde, or a ketone produces no precipitate upon reaction with 2,4-dinitrophenylhydrazine and causes ceric nitrate reagent to turn a reddish color. The unknown is most likely A. a conjugated aldehyde. B. a conjugated methyl ketone. C. an unconjugated methyl ketone. D. an alcohol. E. an aromatic ketone.
an alcohol
In the Schiff test, a color change from colorless to magenta indicates the presence of A. a methyl ketone. B. an aldehyde. C. a conjugatged ketone. D. a ketone.
an aldehyde.
For a 2,4-dinitrophenylhydrazone a yellow color indicates the presence of A. a conjugated carbonyl group. B. an aldehyde. C. an unconjugated carbonyl group. D. a methyl ketone.
an unconjugated carbonyl group.
An unknown which was either an alcohol, an aldehyde, or a ketone produced a yellow solid upon reaction with 2,4-dinitrophenylhydrazine, gave a negative Schiff test (no color formed), and a negative iodoform test. It can be concluded that the unknown is A. an unconjugated aldehyde. B. an unconjugated ketone in which neither of the groups attached to the carbonyl is a methyl group. C. a conjugated ketone in which neither of the groups attached to the carbonyl is a methyl group. D. an unconjugated methyl ketone. E. an alcohol.
an unconjugated ketone in which neither of the groups attached to the carbonyl is a methyl group.
If the carrier gas flow rate in a gc experiment were decreased, the retention time of a peak would ("become longer", "become shorter", or "not change"?)
become longer
if the gc column temperature were decreased, the retention time of a peak would ("become longer", "become shorter", or "not change"?)
become longer
If the carrier gas flow rate in a gc experiment were increased, the retention time of a peak would ("become longer", "become shorter", or "not change"?)
become shorter
if the gc column temperature were increased, the retention time of a peak would ("become longer", "become shorter", or "not change"?)
become shorter
What structural characteristic of thalidomide accounts for the fact that in one form it acts as a sedative and in another it acts as a teratogen? A. solubility in lipophilic solvents B. polarity C. heat of formation D. chirality E. steric properties
chirality
A mixture of which two compounds is distilled in the first part of the experiment? A. toluene B. cyclopentane C. xylene D. octane E. cyclohexane
cyclohexane and toluene
After considering the results of the classification tests, the possibilities can be narrowed down further by determining the melting point of the A. Schiff addition product. B. triiodo compound. C. derivative. D. iodoform.
derivative.
The purity of the distilled cyclohexene is determined by A. thin layer chromatography. B. nuclear magnetic resonance spectroscopy. C. infrared spectroscopy. D. measuring the amount of dibromide formed in its reaction with bromine in dichloromethane. E. gas chromatography.
gas chromatography.
In the gc used in your laboratory, the carrier gas is A. helium. B. argon. C. nitrogen. D. sulfur hexafluoride. E. oxygen.
helium
In the purification of cyclohexene, the purpose of adding calcium chloride to the solution is to A. promote smooth boiling. B. help remove water. C. remove excess organic solvent. D. react with excess permanganate. E. destroy excess bromine
help remove water
In the purification of cyclohexene, the purpose of extracting with saturated aqueous sodium chloride solution is to A. help remove water from the solution. B. prevent hold-up in the distillation apparatus. C. react with calcium chloride. D. decompose excess bromine. E. decompose excess potassium permanganate.
help remove water from the solution.
The following compound, nonanol, would be expected to be most soluble in which of the following solvents (choose one): A. hexane B. acetic acid C. water
hexane
If you receive a minor burn from a hot object, the first thing to do is to A. immediately place the burned tissue under warm water. B. ask the Teaching Assistant for medication. C. immediately place the burned tissue under cold water. D. go to the infirmary.
immediately place the burned tissue under cold water
Soap molecules dissolved in water form an aggregate called a A. micelle. B. globular cluster. C. detergent. D. carbonaceous chondrite E. scrubbing bubble.
micelle.
Information about the number of neighboring hydrogens each hydrogen has can be obtained from the A. number of signals. B. positions of the signals. C. multiplicity of the signals. D. relative areas of the signals
multiplicity of the signals.
Information about functional groups may be obtained from examining the A. relative areas of the signals. B. multiplicity of the signals. C. positions of absorption or chemical shifts. D. number of signals.
positions of absorption or chemical shifts.
In a distillation the purpose of using a chaser is to
prevent loss of product due to hold-up in the apparatus.
In the bromine test, the presence of an alkene is indicated by a color change of A. reddish-orange to purple. B. colorless solution to a brown precipitate. C. purple to colorless. D. colorless to reddish-orange. E. reddish-orange to colorless.
reddish-orange to colorless
When two liquids that are mostly insoluble in one another are mixed together, they separate out into two layers. Whether one liquid is the upper or lower layer depends upon the A. relative densities of the two liquids. B. functional groups present. C. molecular weights of the two liquids. D. the solubilities of the two liquids.
relative densities of the two liquids.
Reaction of an alcohol and a carboxylic acid to form an ester is an equilibrium reaction. In your experiment the method used to drive the equilibrium towards product and thus to obtain the maximum yield of ester is to A. use an excess of carboxylic acid. B. use an excess of alcohol. C. remove ester as it is formed. D. remove water as it it is formed. E. use an excess of both alcohol and carboxylic acid.
remove water as it it is formed
Reaction of an alcohol and a carboxylic acid to form an ester is an equilibrium reaction. In your experiment the method used to drive the equilibrium towards product and thus to obtain the maximum yield of ester is to A. use an excess of alcohol. B. use an excess of both alcohol and carboxylic acid. C. remove ester as it is formed. D. use an excess of carboxylic acid. E. remove water as it it is formed.
remove water as it it is formed.
Which test distinguishes between aldehydes and ketones? A. Conjugation test B. Schiff test C. Iodoform test D. 2,4-Dinitrophenylhydrazine test
schiff test
The correct amount of solvent to use in a crystallization is A. the minimum needed to dissolve the solid near the boiling point of the solution. B. five mL per gram of solid. C. twice the minimum needed to dissolve the solid near the boiling point of the solution. D. the minimum needed to dissolve the solid at room temperature.
the minimum needed to dissolve the solid near the boiling point of the solution.
The number of different hydrogen environments in a molecule can be inferred from A. the number of signals in the spectrum. B. the areas of the signals. C. the positions of the signals. D. the multiplicity of the signals.
the number of signals in the spectrum
The relative number of hydrogens in each different environment can be determined from A. the positions of the signals. B. the multiplicity of the signals. C. the number of signals. D. the relative areas of the signals
the relative areas of the signals.
The following molecule, a sugar with five carbons and five OH groups, would be most soluble in which of the following solvents? A. Hexane B. Water C. Any nonpolar solvent D. toluene
water
A sample of glucose is added to a mixture of water and tert-butyl methyl ether. The glucose will dissolve mostly in the _____(ether or water?) layer. The water layer will be the ____ (upper or lower?) layer?
water, lower
