Chemistry 237 Lab Exams
To separate two compounds by liquid-liquid extraction, the compounds must
be distributed unevenly between two immiscible liquids
Volatile organic compounds should
be transferred in the hood
A mixture of benzoic acid, benzyl chloride, and cyclohexyl amine is dissolved in dichloromethane. The solution is extracted with dilute aqueous HCL and the layers separated. The dichloromethane layer contains
benzoic acid and benzyl chloride
When determining the melting point of a sample, rapid heating causes the observed melting point range to be
broad and high
When you do a recrystallization experiment, the impurities should either be very insoluble or highly soluble in the recrystallization solvent. If they are insoluble they may be removed by ________________ at ______________________ temperatures
filtration; high
Assuming you had a mixture of the following compounds, which one would elute first on a GC that contains a polar poly-alcohol column
hexane-the thing that comes out first is non-polar which is hexane
In simple distillation, the temperature frequently drops after the main fractions have distilled because:
impurities begin to distill
Of the three mono-substituted cyclohexanes shown, the trimethytin substituent in A has the smallest steric hindrance because
it has a longer axial bond length
What effect on the rate of an SN1 type reaction would there by if you doubled the concentration on the nucleophile?
it would have no effect on the rate.
If you take the melting point of an impure substance, the observed melting point range will be _________________________________ relative to the melting point range observed for the pure substance
lower and broader
In normal phase thin layer chromatography, the stationary phase is
polar
Absorption of infrared radiation by a molecule
produces changes in the amplitude of molecular vibrations.
In the recrystallization of acetanilide, you were asked to allow the hot solution to cool slowly to form crystals. What happens if the solution is cooled rapidly?
small crystals form and adsorb impurities
You have carried a synthesis and the pot contains your product (a liquid which you plan to distill) and one impurity. You will have to carry out a fractional distillation in order to recover the product in good purity if the impurity is
soluble in the product and volatile
What is the hybridization of the oxygen atom and the approximate bond angles around oxygen in methanol, CH3OH?
sp3 and 109.5 degrees
Which of the following would not be a role of the phase transfer catalyst?
Aids in the separation of the products of the reaction
Which of the following functional groups has sp hybridization?
Alkyne
Which of the following items is not true of the mini-column used in the phase transfer catalysis?
Any leftover starting material eluted off the column before the product.
When hexane was used as the solvent for your Analgesics TlC lab, why didn't the spots move?
Hexane is not able to disrupt the polar-polar interactions between the analgesics and the silica gel
What observation would be most conclusive in determining that the following compound was successfully oxidized to a carbonyl product?
IR band at 1710 cm(-1)
Which of the following statements is false for recrystallization as a method of purification of organic compounds?
If the impurities are soluble, they may be removed by filtration at high temperature.
Which of the following statements about gas chromatography is false?
If the stationary phase is polymeric alcohol, a nonpolar compound would move more slowly than a polar compound
What is the chemical formula of the precipitate formed in the Bayer's test?
MnO2
Which chemical was used to destroy excess oxidant in the oxidation of a 2 degree alcohol
NaHSO3
Which of the following statements about gas chromatography is true?
Polar compounds are more retained by polar columns
Infrared spectroscopy may be used to distinguish a primary amine from a secondary amine because?
Primary amines show two absorptions at 3400-3100 cm(^-1) and secondary amines show only one absorption at 3400-3100 cm(^-1)
In the kinetics experiment, two different solvent mixtures were used. One mixture was 50% water-50% ethanol, the other was 60% water-40% ethanol. What would you predict about the rates in the two solvent mixtures
The rate in the 60% water-40% ethanol mixture would be faster because the solvent better stabilizes the cation
The rate constants for an SN1 solvolysis of 1-phenyl-1-chloroethane are 3.0E-5 sec-1 for a 40:60 H20/EtOH solvent mixture and 4.0E-4 sec(^-1) for a 50:50 H2O/EtOH solvent mixture. The rate constant, k, is larger for the 50:50 H20/EtOH mixture because
the 50:50 mixture is more polar
Which statement is true about thin layer chromatography?
the solvent moves through the stationary phase by capillary action.
In a distillation, one vaporization and condensation step is usually called a(n):
theoretical plate
In the phase transfer catalysis experiment, the role of benzyltri-n-butylammonium chloride is
to carry the naphtolate anion to the organic phase.
In the solvolysis reaction of 1-chloro-1-phenylethane, what is the nucleophile
water
Which of the following is the most polar compound?
water
A phenol (ArOH) that is deprotonated by NaOH will become
(ArO-); Na+
VSPER theory
1)sp-2 regions of electron density-180 degrees 2)sp2-3 regions of electron denisty-120 degrees 3)sp3-4 regions of electron denisty-109.5 degrees Lone pair, single bond, double bond, and triple bond all count as one region of electron density.
How many hydrogen atoms are removed during the oxidation of 3-heptanol to 3-heptanone?
2 hydrogen atoms
The computer calculated that the local minimum for the gauche butane conformation had a dihedral angle of:
65 degrees Celsius
The distillate collected whilst dehydrating cyclohexanol is an azeotropic mixture of cyclohexane and water. What is the composition ratio of cyclohexene to water?
90:10
In the Who Has My Compound experiment, which technique did you not use to determine your compound?
Boiling point determination
The product of the dehydration of cyclohexanol gives a positive result to which of the following tests?
Bromine and Baeyer's Test
The global minimum energy for conformations of butane occurs when?
C1 and C4 are in an ANTI position. If the question asked for Local minimum energy, it would be gauche.
In infrared spectroscopy, which of the following statements is true?
C=O has strong absorption in the range of 1600-1800 cm^-1
A positive bromine test indicates the presence of what?
Carbon-Carbon double bonds
In the oxidation reaction with sodium hypochlorite, the oxidant (oxidizing agent) is reduced into
Cl-
When performing the bromine test, what does a positive result look like/indicate
Color disappears, double bonds are present
Which of these statements about the column with a typical GC is false?
Column contains an inert, powdered solid
If you have a sample that is known to be either adipic acid or acetanilide, what is a quick way to distinguish the two
Determine the solubility of each in sodium bicarbonate
Which of the following statements about gas chromatography is false?
GC is preferred when a great amount of mixture is available for separation.
Which reagent is not an oxidizing agent?
H20
To form a salt of an amine, R-NH2, you must add which reagent
HCl
Which statement is true for the following reaction
RX and R-OAr are soluble in the organic phase. (Allyl bromide is soluble in organic solvent, but insoluble in water) (Naphtholate ions are water soluble, but practically insoluble in organic solvents)
In the thin layer chromatogram of a mixture of two compounds A and B, as the solvent moves up the plate
Rf(A) and Rf(B) remain constant and the separation of A and B increases
When you want to remove the water dissolved in an organic phase, the easiest way to wash this solution is with brine. What is brine?
Saturated NaCl solution
Which one of the following statements would not be desired in a good recrystallization solvent?
The recrystallization solvent is nonvolatile.
Which of the following does not influence the separation of a mixture of compounds in gas chromatography?
the densities of the compounds in the sample
which of the following statements about extraction is false
the extraction solvent should form an emulsion with the other liquid
The boiling point of a liquid is not affected by
the rate of heating
In TLC, a Rf value is:
the ratio of the distance the compound moved by divided by the distance the solvent moved.
Why is it important not to distill a flask/vial to dryness
the residue in the flask could explode
