Final Organic Chemistry Lab Exam
In the permanganate test, the presence of an alkene group is indicated by
formation of a brown precipitate. a color change from purple to colorless.
Which of the following organic solvents would be suitable for use in the extraction of an aqueous solution?
hexane. One requirement of an extraction solvent is that it be mostly insoluble in water
One triglyceride present in animal fats is tristearin (glycerol trioctadecanoate). What is the theoretical yield, in grams, of stearic acid upon hydrolysis of 1.8 g of tristearin?
(1.8g)(1mol/891.48g)=0.0020 moles tristearin (0.0020moles)(3)=0.0060moles (0.0060 moles)(284.5/mol)=1.7g
Hydrolysis of 0.016 mol of the fat, trimyristin, yields how many grams of myristic acid (MW = 228)?
-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 = 22830.016 = 11.0
If the carrier gas flow rate in a gc experiment were decreased, the retention time of a peak would...
-become longer. In gas chromatography, increasing the carrier gas flow rate through the column will cause all compounds to travel through the column more quickly. Decreasing the flow rate will cause all compounds to travel through more slowly. Flow rate is adjusted so that peaks will be sufficiently separated within a reasonable amount of time. Too high a flow rate will cause all compounds to travel through too rapidly with little or no separation.
If 0.021 mol of cyclohexanol reacts with 0.016 mol of 85% phosphoric acid, the theoretical yield of cyclohexene is _______ mol.
0.021 mol. 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.
If 0.029 mol of cyclohexanol reacts with 0.011 mol of 85% phosphoric acid, the theoretical yield of cyclohexene is ____ mol.
0.029
Name the alcohol and carboxylic acid (in that order) used to make the ester, n-propyl
1-propanol pentanoic acid
If the resulting solution in question 3 were cooled to 14° C, how many grams of phthalic acid would crystallize out? What would be the percent recovery?-first we should take the solubility data from text book
18 gram will dissolve in 100 mL of water so fro 4.2 gram how much boiled water =100 x 4.2/18 = 420/18 = 23.34 boiling water again from text book at 14 degree 0.54 gram will dissolve in 100 mL water 0.54 x 23.34 / 100 = 0.126 4.2 - 0.126 = 4.074 gram thalic acid will recrystalize
The catalyst used in the dehydration of cyclohexanol is
85% phosphoric acid
If the gc column temperature were decreased, the retention time of a peak would ..
Become longer
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.
During which step or steps is most of the excess carboxylic acid removed?
Carboxylic acid is soluble in water and reacts with sodium bicarbonate, so it is removed during the extraction phase of this experiment.
In a TLC analysis, if the Rf of a compound was found to be too small, a ________(spotting or development?) solvent having a ______(lower or higher?) polarity should be chosen.
Development, higher
With respect to GC, what effect would raising the column temperature have on the retention time?
Higher temperature in the GC analysis column would result in a shorter retention time. This is due to the liquid vaporizing faster, causing the vapor to reach the detector faster, and shortening the retention time
Starting with 1.20 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?_____ g The amount of product obtained after the final distillation is 0.836. 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 0.720, what is the % yield of pure cyclohexene? ______%
Hydrolysis of 0.016 mol of the fat, tripalmitin, yields how many grams of palmitic acid (MW = 256)? 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 = 25630.016 = 12.3
MP Two test tubes contain compounds having the same MP. Using MPs, how could you determine whether the two test tubes contain the same or different compounds?
If a mixture of A+B, A+C, or B+C is made, a depression of melting point will prove whether or not two compounds having the same melting points are identical. If the two substances in the mixture are identical, the mixture will have the same melting point. If the two substances in the mixture are different, the mixture will have a reduced melting point.
The Rf of ibuprofen was found to be 0.32 when neat t-butyl methyl ether was used as the development solvent. What effect would there be on the Rf of ibuprofen if acetone had been used to develop the TLC plate?
If the TLC plate is run with Acetone then RF value is more,because Acetone is more polar than t-butyl methyl ether ,so Acetone carriers the ibuprofen to more distance than t-butyl methyl ether.the distance travelled by the ibuprofen is more ,so RF increases.
What is the structural difference between saturated, monounsaturated, and polyunsaturated fats? Of which kind is trimyristin?
If the carboxylic acid portion of the fat contains no alkene groups, the fat is said to be saturated. If one alkene group is present the fat is monounsaturated. If more than one alkene is present the fat is polyunsaturated. In a monounsaturated fat, if the alkene is one carbon in from the far end of the long chain (away from the ester group), the fat is said to contain omega-1 (read as omega minus one - omega refers to the end of the chain so omega-1 refers to one carbon in from the end) fatty acids. Trimyristin is a saturated fat.
What does Ce+4 tell you ?
If the color changes from yellow to red it confirms that you have an alcohol. If there is no color change than you do not have an alcohol.
What does Schiffs test tell you?
If there is a magenta color change than you have an aldehyde. If there is no color change than you have a ketone.
Using the information given in this handout, how many mL of boiling water are required to dissolve 4.2 g of phthalic acid?
Phthalic acid soluble in hot water 18g/100ml, 14 degrees 0.54g/100ml 18-0.54=17.46 17.47/18x100=97.05 100ml/18g=55ml for 1g of ophthalmic acid 4.2gx55ml=23.31ml 4.2x 97.05/100=4.076 grams will be recovered.
The iodoform test indicates what?
The iodoform test indicates the presence of an aldehyde or ketone in which one of the groups directly attached to the carbonyl carbon is a methyl group
To isolate the benzoic acid from the bicarbonate solution, the bicarbonate solution is acidified with concentrated HCl. What volume of acid is required to neutralize the bicarbonate?
The molar amount of bicarbonate left over will depend on the amount of benzoic acid in the original mixture made for your lab experiment. Here we are assuming 0.10g benzoic acid was recovered acid was recovered from the original mixture. If 0.10g benzoic acid (8.2x10^-4 mol) was reacted with 1 mL of a 10% solution of NAHCO3 (1.2x10^-3mol) the amount of excess NaHCO3 can be calculated subtracting the amount of benzoic acid from the amount of NAHCO3. 1.2x10^-3-8.2x10^-4 mol=3.8x10^-4 mol. Concentrated HCL is 12M. HCL ad NAHCO3 react with a 1:1 stoichometry, so to determine the volume of concentrated HCL needed, divide the molar amount of excess NAHCO3 by the concentration of the HCL solution. (3.8x10^-4 mol)(1L/12mol)(10^3ml/1L)=0.032 mL
If the carrier gas flow rate in a gc experiment were decreased, the retention time of a peak would..
become longer
Briefly describe how soluble impurities are separated from the desired compound, at the molecular level.
To remove soluble impurities, first, by doing solubility tests, a suitable solvent is chosen (high solubility in hot solvent, low solubility in cold solvent). The soluble impurities are then removed as follows: the desired compound along with the soluble impurities are dissolved in a MINIMUM of near or at BOILING solvent. The solution is then allowed to cool slowly and without interruption. As the solution cools, the solubility of the compound (and of the soluble impurities) decreases, the solution becomes saturated with the desired compound, and the compound begins to crystallize. Because formation of crystals is a highly selective process that usually excludes foreign molecules, only crystals of the desired compound form. Because the soluble impurities are present in smaller amounts, the solution never becomes saturated with the impurities, so the impurities remain in solution even after the solution has cooled. Removing the solution from the crystals thus removes the solvent and the soluble impurities from the desired crystals. A final rinse with a MINIMUM of ICE- COLD solvent, followed by its removal, cleans off any residual soluble impurities clinging to the surface of the desired crystals.
What does I2/OH- tell you?
Yellow ppt means methyl aldehyde/ketone. No ppt means not methyl Aldehyde or Ketone.
In a TLC analysis if the Rf's of the spots are too small then..
a development solvent of higher polarity should be used.
Select the four characteristics of a proton NMR spectrum that are used to help interpret
area position multiplicity number of signal
If the gc column temperature were increased, the retention time of a peak would
become shorter. In gas chromatography, increasing the temperature of the column will cause all compounds to travel through the column more quickly. Decreasing the temperature will cause all compounds to travel through more slowly. Column temperature is adjusted so that peaks will be sufficiently separated within a reasonable amount of time. Too high a temperature will cause all compounds to travel through too rapidly with little or no separation.
The correct amount of solvent to use in a crystallization
the minimum needed to dissolve the solid near the boiling point of the solution.
In a TLC analysis of analgesics, what would be the result if a solvent of too low polarity is used to develop the plate?
if solvent s are too low polarity all compounds will get same rf value.
Arrange the following compounds in order of increasing Rf in a TLC analysis: benzoic acid, benzaldehyde, 3-heptanone, nonane, and cyclohexanol.
increasing order is :Benzoic acid( most polar), cyclohexanol, benzaldehyde, 3-heptanone, nonane(less polar)
Starting with 3.60 g of cyclohexanol, what is the theoretical yield of cyclohexene in mol (do not add the units to these answers)? What is the theoretical yield in g? The amount of product obtained after the final distillation is 2.06. 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 0.660, what is the % yield of pure cyclohexene?
mol cyclohexanol= 3.6g/100.2= 0.036 mol 1 mol cyclohexanol -------1 mol cyclohexene 0.036mol cyclohexanol ------ x=0.036 mol cyclohexene (this is the theoretical yield) mol cyclohexene= mass/82.1 =0.036mol ------> mass= 2.96g (theoretical yield in g) % yield= obtained amount/ theoretical yield x 100= 2.06/2.96 x 100= 70% I assume that the product is 0.660% pure, but in the exercise it`s not clear. from 2.06g only 0.66% is pure so, 2.06g ------100% x-------------0.66% x= 0.0136g pure %yield= 0.0136/2.96 x 100= 0.46%
The number of different hydrogen environments in a molecule can be inferred from
the number of signals in the spectrum
The relative number of hydrogens in each different environment can be determined from
the relative area of the signals
In this experiment, if the carboxylic acid is benzoic acid, how many moles of benzoic acid are present (assume an equal portion of each component)? How many moles of sodium bicarbonate are contained in 1 mL of a saturated aqueous sodium bicarbonate. Is the amount of sodium bicarbonate sufficient to react with all of the benzoic acid?
molar mass of Benzoic acid =122 gm, moles of benzoic acid in 0.1385 gm= mass/molar mass= 0.1385/122= 0.001135 at room temperature , solubility of NaHCO3 is 96 gm per 1000ml 1000ml of solution contains 96 gm of NaHCO3 1ml contains 96/1000 gm of NaHCO3= 0.096 gm , moles of NaHCO3= mass/molar mass= 0.096/84= 0.001143 the reaction between benzoic acid and NaHCO3 is C6H5COOH+ NaHCO3 ------>C6H5COONa+ H2O+CO2 theoretical molar ratio of acid to base = 1:1 actual molar ratio = 1:1 hence sufficient NaHCO3 is available.
A suitable crystallization solvent is ?
one in which the solid has a low solubility in cold solvent and a high solubility in hot solvent.
Information about functional groups may be obtained from examining the
positions of absorption or chemical shifts.
The fat, triolein, when hydrolyzed with aqueous NaOH followed by acidification with HCl yields glycerol and oleic acid. If 0.015 mol of triolein is hydrolyzed, what is the theoretical yield of oleic acid in moles?
triolein + ... → 3 oleic acid + ... (0.015 mol triolein) x (3/1) = 0.045 mol oleic acid
