chem final lab
Near the end of a distillation of hexane/nonane mixture, which compound will predominately remain in the boiling flask?
nonane
Which of the following is halogenated?
o-chlorobenzoic acid
Which of the following will be most soluble in hot water?
o-chlorobenzoic acid
Which of the following is in correct order of decreasing IR stretching frequency?
Alkynes > alkenes > alkanes
which have a higher vapor pressure? Hexane or nonane?
Hexane
Why are some fundamental vibrations not observed?
They exist outside of the mid-IR (observed) region. They are too weak or overlap with other vibrations. They are degenerate with other vibrational modes.
A mixture of two components is evaluated by GC. Given a peak area of 14.7 for compound 1 and a peak area of 4.3 for compound 2, what is the % composition of compound 1 in the mixture?
(area1 / area1 + area2) * 100 = % compound1. (77.3684210526)
What is the volume of 2.5 mmol of butan-2-ol (shown)? Your answer should be in mL, just give the number. Your answer should have 2 significant digits at least (2nd decimal place).
.23
What is the theoretical yield of butan-2-one (shown) if 0.30 mL of butan-2-ol is treated with TEMPO and an excess of of TCCA and is completely oxidized? Your answer should be in grams and give only the number. Your answer should have at least 2 significant digits (2nd decimal place).
.24
If a spot on a TLC plate travels 4.5 cm from the starting spot when the solvent moves 6.0 cm, what is the Rf value of the spot? Answer the question to 2 decimal places.
.75
What is the density of a liquid whose mass of 120 μL is 98 mg in g/mL? Enter number only without units to at least 2 decimal places.
.82
What should the reading be on a balance displaying mass in grams be for a sample weighing 50mg?
0.050 g
What is the expected yield of this reaction assuming 0.230 g of acetaminophen is used along with all of the other starting amounts of reagents listed in this experiment? Your answer should be in grams and answer to the 3rd decimal place.
0.273
What is the density of water at room temperature in g/mL? Give just the number and not the unit.
1 g/ml
What is a good temperature to set the hot plate to for safely and effectively warming a shell vial with 1 mL of ethanol for recrystallization?
100 degrees C
What size filter paper should be used with a Hirsch funnel?
10 mm
H2O is a bent, non-linear molecule consisting of three atoms. Count the number of functional vibrations and type the number in the box below (can you name them all?).
3
How many μL are in 0.040 mL? Type number only without units.
40
What is a good choice of solvent system to separate the follow molecules shown below?
50:1 ethyl acetate: acetic acid
Assuming 8 mL of cyclohexanol is used in this reaction, what is the theoretical yield in grams? Answer to two decimal places and do not include the unit.
6.27
What is a good choice of solvent system to separate the follow molecules shown below?
A and C
Which of the following statements about IR spectroscopy is FALSE?
Absorptions due to C=O bond stretching are generally weak.
A solution is considered dry (i.e., devoid of water) when which of the following cases is true?
After treatment with an anhydrous salt, the salt clumps together significantly but also has several crystals that do not clump with any other crystal.
Keeping all other variables the same, which of the following bonds would have the lowest IR stretching frequency?
C-CL
The stretching frequency of which functional group would be most useful in the detection of metal ligand complexes?
C-O
Which of the following is NOT a factor that affects retention time?
Concentration of the sample
What is the primary mechanism involved in this experiment? Experiment 11: Dehydration of Cyclohexanol
E1
How much anhydrous magnesium sulfate is required to dry a diethyl ether solution after preforming extractions involving water?
Enough such that some powder remains free flowing in solution with swirling without clumping.
When evaporating solvent from a solution by gently blowing compressed air on it, why is it helpful to warm the solution?
Evaporating solvent removes heat energy from the solution and container, cooling it in the process and decreasing the vapor pressure of the liquid. Warming the solution counters this.
What type of detector is most commonly used in GC?
Flame ionization detector (FID)
Which of the following lists the electromagnetic radiation in correct order by increasing wavelengths?
Gamma rays, ultraviolet radiation, microwaves, radio waves
What are some of the possible sources of IR absorbance that a background scan may collect?
H2O and CO2
Name one of the two gases typically used in GC analysis.
He, helium, nitrogen, N2, helium gas, nitrogen gas
Why should you vent the separatory funnel periodically when preforming an extraction involving organic solvents?
Mixing increases the evaporation of volatile organic solvents creating pressure in the closed space of a separatory funnel.
Sort the following molecules in order of increasing Rf value assuming a silica TLC plate was used with a 10:1 hexanes: ethyl acetate solvent system.
NH2, NH, Cl, none
Which should have a higher boiling point? Hexane or nonane?
Nonane
simple vs fractional distillation ?
Simple distillation is more effective when there is a large difference between the boiling points of the two compounds (at least a 50°C difference is ideal in simple distillation). If there is a smaller difference between the boiling points (e.g., hexane and nonane), a simple distillation can be represented
Which of the following affect the amount of signal from the FID? Choose all that apply.
The amount of compound in the sample being analyzed and the number of carbon atoms in the compound being analyzed.
Why is it important not to heat the solid caffeine left after the solvent has been evaporated in the final evaporation to long once the solvent is completely evaporated?
The caffeine can sublime decreasing your yield.
How does a the increased surface area of a fractionation column help in fractional distillations?
The increased surface area provides surfaces for the distillate gasses to condense and then a portion of that condensed liquid to re-vaporize.
The shift in the C=O stretching frequency in a metal-ligand complex is influenced by all of the following, except what?
The intensity of the infrared source used.
purpose of simple distillation ?
The purpose of a simple distillation is to remove one volatile liquid from another less volatile liquid or nonvolatile substance. This is required when a liquid compound needs to be removed from a solvent (e.g., after an extraction) or as a purification process when the impurities and the product have significantly different volatilities.
What is retention time?
The time lapsed between when a sample is injected into the GC instrument a compound hits the detector.
Which layer will be the ether layer in a separatory funnel containing diethyl ether and a saturated aqueous solution of NaCl?
The top layer.
In order for an IR vibration to be allowed, what condition must be met?
There must be a change in dipole moment of the molecule.
Why is it important to have water slowly running through the condenser?:
Water absorbs heat from the distillate gases allowing it them to condense back into a liquid for collection.
Keeping all other variables the same, as bond strength decreases which of the following changes occur?
Wavenumber of the IR stretch decreases
What is the limiting reagent in William Ether Synthesis?
acetaminophen
Imagine you just ran a silica TLC plate for a reaction in which you expect two products. You obtained a Rf value of 0.95 using 1:1 hexanes: ethyl acetate developing solvent system, what should you do?
add more hexanes to the solvent system
During the reaction work up, pentane is used as an organic solvent and there are aqueous extractions. Which layer is most dense? organic or aqueous? in Dehydrohalogenation of 2-Bromoheptane
aqueous layer
What is the role of potassium carbonate in WES?
base
Which layer will be the organic layer during the aqueous tea dichloromethane extraction process?
bottom layer
What is the leaving group in the reaction for Experiment 10: Dehydrohalogenation of 2-Bromoheptane?
bromide anion
What role does the phosphoric and sulfuric acids play in this reaction? Experiment 11: Dehydration of Cyclohexanol
catalyst
Before developing a TLC plate you should _______.
check to see if the correct amount of material is spotted with a UV lamp if possible
From your plots of temperature vs volume of distillate for the simple and fractional distillations of the mixture, which method do you conclude is more effective at separation? Explain your reasoning.
depends on the properties of the total mixture and the individual components. For both techniques, the components of the mixture MUST be miscible (soluble) in one another. For a simple distillation, the components of the mixture should have boiling points separated by at least 30 °C. If the components of the mixture have boiling points that are separated by less, fractional distillation is a better choice.
What term best describes the cis and trans isomers of an alkene like 1,2-dibenzoylethylene?
diastereomers
What mobile phase should you use to develop your TLC plages?
dichloromethane
During the extraction procedures, which layer has the higher density? dichloromethane or aqueous layer? in WES
dichloromethane layer
Which distillation method will give a purer sample of whatever distills first from a hexane/nonane mixture?
fractional distillation
Where should the solid from the initial reaction mixture that should have ended up in the bottom of your centrifuge tube be disposed?
halogenated waste
what not to do in a distillation?
heat in a closed system and distill to dryness
In a distillation of a hexane/nonane mixture, which compound will predominate in the first drops of distillate?
hexane
What characteristic is required for gases used in GC? Gases must be .
inert
Simple distillation is more effective when there is a __ difference between the boiling points of the two compounds.
large
In normal-phase TLC, a compound with a Rf value of 0.7 is _______ polar than a compound with a Rf value of 0.4
less
Sort the molecules below in order in increasing Rf value if a reverse-phase TLC plate was used with a water: acetontrile developing solvent.
less complicated, intermediate complicated, most complicated
What is the rate limiting step in this reaction?
lose of water to generate a carbocation
During the washing/extraction portions of product isolation, which layer has a higher density? aqueous or organic
organic
Electrons in what kind of bond are excited by photons in this experiment?
pi bond
What is the stationary phase in the column used for this course?
polymethylphenylsiloxane
Which of the following reagents can cause serious eye damage?
potassium tert-butoxide, sodium methoxide, 10% potassium hydroxide solution
Which of the following reactions will promote an E2 reaction with an alkyl halide?
sodium ethoxide
What is the role of 2-butanone in WES?
solvent
What role does dichloromethane play in this experiment? (OXIDATION OF ALCOHOL and IR spec)
solvent
What role does methanol and tert-butanol play in the reaction for Experiment 10?
solvent
Which layer will the caffeine preferentially dissolve in during the aqueous tea dichloromethane extraction process?
the dichloromethane layer
What is a cause of spots streaking across a TLC plate?
too much sample
During the extraction of the distillate, which layer will be the organic phase in the separatory funnel?
top layer
Which isomer of 1,2-dibenzoylethylene is most stable? Ex. 12
trans
