Exam I LM and Pre-Lab

You are asked to determine the thermometer correction for your assigned melting point apparatus. You obtain a pure sample of benzoic acid and determine its melting point range carefully. After several trials, you obtain a very sharp melting point of 127.9 degrees celsius. What is the thermometer correction at this temperature? For purposes of these questions, the melting point of very pure benzoic acid is 122.4 degrees Celsius. (The thermometer correction is the value that must be added to the observed thermometer reading. You have to type in your answer with a + or - sign. )

-5.5

The following boiling temperature/composition data were obtained for a mixture of octane (O) and methylbenzene (M) at 760 torr, where x is the mole fraction in the liquid and y the mole fraction in the vapour at equilibrium. The boiling points for M and O are 110.6 °C and 125.6 °C, respectively. Plot the boiling temperature/composition diagram for the mixture using Excel. What is the composition of the vapour in equilibrium with the liquid of composition xM = 0.25?

0.36

n a thin layer chromatography experiment, a plate of length 9.7 cm was used and a horizontal line was made at 1.3 cm above the bottom of the plate. After running the experiment (developing and drying), a spot was observed at 5.1 cm from the bottom of the plate, and the solvent front was 8.1 cm from the bottom of the plate. What is the Rf value

0.559

Visualization of spots/compounds on the TLC plate under UV light is only applicable to compounds that absorb light in the same wavelength region as UV light in use

True

If lights enters a material and is found to have a speed of 2.03×108, what is the index of refraction for that material?

1.48

Light travels fastest when traveling through a vacuum. The speed of light in a vacuum is 3.00×108 m/s. When light enters a material, such as water or glass, it slows down. The new speed is related to a quantity called the index of refraction of a material. Refer to Section 1.1 of "Physics in the Arts" to answer the following problem.If light enters a material which has an index of refraction of 1.67, what is its speed in that material?

179640718.5629 m/s

2-Methoxy-4-(prop-2-en-1-yl) phenol commonly known as eugenol is a colorless to pale yellow, fragrant oil extracted from cloves, basil, cinnamon and nutmeg. A student working in a natural products research lab isolated 1.3 grams of eugenol by steam distilling 5.00 grams of cloves. Calculate the student's % recovery of eugenol. (Answer format - e.g., 33.3% should be entered as 33.3 without the percent -%)

26

The temperatures at which the vapor pressures of the following liquids are all 100 torr are given. Predict the order of increasing boiling points of the liquids.

3: 1-propanol, (C3H8O), 52.8°C 2: ethyl methyl ether, (C3H8O), -34.8°C 1: propane (C3H8), -79.6°C

In a recrystallization from boiling water of benzoic acid contaminated with acetanilide, you begin with an impure sample of 3.00 grams. If the % composition of the acetanilide impurity in the sample is 5.0 what is the minimum amount in mL of solvent (water) required for the recrystallization? (Answer format - e.g., 33.2 mL should be rounded off to nearest whole number and entered as 33 without any units)

51

A student was tasked with recrystallization of 4.0 grams benzoic acid contaminated with 9.6% acetanilide. After several recrystallizations, a dry sample 2.88 grams of pure benzoic acid, as determined by melting point measurement, was obtained. Calculate the percent recovery of benzoic acid?

72

If a mixture of A and B has this melting point diagram, at what temperature would all of the sample melt if the mole fraction B is 0.20?

86ºC

When using a separatory funnel containing two immiscible solvents [i.e., organic and aqueous solvent] it is important to identify which solvent is the top layer and which solvent is the bottom layer. Which factor determines which layer rest on top and which rest on the bottom?

Density

Identify the intensive property from the following:

color

A Chem 335 student is setting up an acid-base extraction experiment in the lab that requires one to start with a sample mixture of approximately 1.30 grams. Order the procedural sequence involved in weighing, on an electronic balance, a solid sample that is to be transferred to another container.

A. Read and record the mass on the digital display. B. Transfer solid in the reaction container.> C. Use a spatula to transfer solid from reagent bottle to weighing container.> D. Wait until the reading on the display remains constant. E. Place the weighing container on the weighing pan. F.Press the appropriate button to set the digital readout to zero.

Outlined below are statements describing the general procedure followed during purification of a solid by recrystallization process. Order the process from start to finish. A. Dissolve the impure solid in hot recrystallization solvent. B. Calculate the approximate volume of solvent required for recrystallization and measure out the amount plus 10-30% extra.> C. Obtain the melting point of solid and calculate % recovery.> D. Remove undissolved material by gravity filtration of hot solution. E. Add decolorizing charcoal to the hot solution to remove the colored impurity. F. Isolate the crystallized solid by vacuum (suction) filtration on a Buchner funnel.

BAEDFC

A student conducted a thin layer chromatography experiment to determine the Rf values of the following compounds. List the compounds in order of increasing Rf values from shortest to longest.

BCAD

Suppose that a mixture of benzoic acid and p-nitroaniline is dissolved in ether. If the ether solution is extracted with aqueous 6M hydrochloric acid, which compound(s) would remain largely in the ether layer?

Benzoic acid would remain in the ether solution.

A Chem 335 student goes into the lab to complete a recrystallization experiment. Part of the procedure involves heating an aqueous solution in an Erlenmeyer flask and bringing it to a boil. Which of the below listed heating sources would be appropriate for this step of the procedure

Correct: Hot plateIncorrect Steam bathIncorrect Oil bathIncorrect Bunsen burnerIncorrect Heating mantleIncorrect Microwave oven

How is Rf (ratio of fronts) defined?

Correct: Rf = (distance travelled by substance) / (distance travelled by solvent front)Incorrect Rf = (distance travelled by substance A) / (distance travelled by substance B)Incorrect Rf = (distance travelled by substance) / (length of the TLC plate)Incorrect Rf = (distance travelled by solvent front) / (distance travelled by substance)

Match each compound with it's solubilty. (Hint: Remember that organic acids are soluble in aqueous bases, and organic bases are soluble in aqueous acids ) ASoluble only in aqueous basesBSoluble only in aqueous acidsCSoluble in ether and weak aqueous bases (eg NaHCO3)DSoluble in ether and aqueous acids (eg HCl)ESoluble in ether, largely insoluble in aqueous solvents

E: NapthaleneC: Benzoic AcidD: Ethyl-4-aminobenzoate

For TLC analysis of cinnamic acid and 2-Methyl-1-phenyl-1-propene using ethyl acetate solvent, it is expected, after development, that the cinnamic acid spot will be approximately ~ 1.6 cm above the 2-Methyl-1-phenyl-1-propene spot.

False

In TLC plate development, the eluting solvent level in the chamber should be above the index mark (the line of initial spot) on the TLC plate.

False

T/F If the mobile phase in a TLC analysis is less polar than the stationary phase the solutes/compounds will migrate faster up the plate.

False

An organic chemist wants to analyze an unknown compound (or mixture) using TLC.S/he uses hexane to develop the TLC plate and finds only one spot with an Rf value of 0.05.S/he can draw the following conclusions:

False: Because the Rf value is small, a polar impurity has to be present.True: The wrong solvent was used, because the Rf value is small.False: There is only one spot, so the compound is pure.False: Based on the Rf value, the compound can be identified from tables.True: Nothing can be deduced regarding the purity.

The thin-layer chromatography (TLC) technique is used for both qualitative and quantitative analysis in organic chemistry laboratories. Which of the functions (applications) listed below apply to TLC technique?

False: Determination of percent composition of components in a crude reaction mixture.True: Monitoring the course of reaction progress by comparing the amount of product formed to the amount of corresponding reagents.False: Determination of optical rotation properties of compounds in a mixture.True: For qualitative identification of unknown substances (unknown components) in a mixture.

Which types of properties may be exploited using gas chromatography?

False: Electronic PropertiesFalse: Basic PropertiesTrue: Physical PropertiesTrue: Chemical Properties

Which of the statements below are TRUE / FALSE concerning the appropriate use of a Digi-Melt SRS?

False: One rapid melting point run is sufficient to make a conclusion about the melting point of a sample.False: The melting point of a sample is recorded at the appearance of the first visible drop of liquid.True: Packing the sample in the melting point capillary tube higher than 3mm results in artificial broadening of melting point range.True: The heating temperature should ideally rise at a rate of 1-2°C/min at the expected melting point of the sample.True: After melting point determination, the melting point capillary tubes should be disposed in the GLASS-WASTE container.False: Melting point correction is conducted to account for errors arising from experimental procedure used to prepare the sample.False: The START and STOP temperature should ideally be set at 20°C below and 20°C above respectively of the expected melting point.

After purifying your sample from the previous question, you determine its melting point to be 122.4 degrees Celsius. Now what conclusion(s) can you reach?

False: The melting point determination may need improvement -- it may not have been done properly, and make sure it was repeated at least once.False: The sample is benzoic acid.False: The sample is not benzoic acid.True: The sample may be benzoic acid.False: The sample is probably impure.

When it comes to visualization of spots on the TLC plate, which of the method(s) listed below are/is considered nondestructive. - Check all that apply.

False: Using 2,4 dinitrophenyl hydrazine reagents to visualize.True: Visualization under ultraviolet light (254 nm)False: Using potassium permanganate ink.True: Direct visualization of colored compounds."False: Using phosphomolybdic Acid (PMA) /ethanol solution.False: Staining with iodine vapors.

Presume you went into the lab and completed a TLC analysis of an unknown analgesic tablet. The analysis yielded the following results. TLC Plate 1: Suppose you spotted 3 reference compounds, acetaminophen, acetysalicylic acid, and caffeine left to right on a plate that was 10 cm long. The index mark was 0.5 cm from the bottom of the plate. After developing and visualizing under UV, you see spots left to right that traveled 2.66, 3.44 (this spot had a long tail), and 0.79 cm from the index mark, while the solvent traveled 8.50 cm from the mark. TLC Plate 2: On a second plate, you spotted an unknown analgesic tablet extract. The unknown was labeled as unknown number 4. This plate that was 10 cm long. The index mark was 0.4 cm from the bottom of the plate. After developing and visualizing under UV, you see spot(s) that traveled from the index mark a distance of 2.54 cm. The solvent traveled 8.10 cm from the mark. In the space provided below calculate and record the Rf values of the reference compounds spotted on plate #1.

I. Acetaminophen: Solute distance = 2.66 cm , Solvent distance = 8.50 cm Rf = Solute Distance / Solvent Distance = 2.66 cm / 8.50 cm = 0.313 II. Acetysalicylic Acid: Solute distance = 3.44 cm , Solvent distance = 8.50 cm Rf = Solute Distance / Solvent Distance = 3.44 cm / 8.50 cm = 0.405 III. Caffeine: Solute Distance = 0.79 cm , Solvent distance = 8.50 cm Rf = Solute Distance / Solvent Distance = 0.79 cm / 8.50 cm = 0.093

Based on the experimental data provided and calculated Rfs results determine (i)the combination of active ingredients contained in your unknown tablet and (ii) identify the unknown tablet

I.Acetaminophen II. Tylenol

You have 3 unlabeled samples. Two are known to be 4-aminobenzamide and one 3,5-dinitrobenzamide. The first melting point tube is a mixed melting point of sample 1 and 2. The second tube is the mmp of samples 1 and 3 while the third tube is the mmp of samples 2 and 3.The tubes have been heated to 180°C. Which sample, 1, 2, or 3 is 3,5 dinitrobenzamide?

Sample 1

Boiling solutions always have the potential to "bump" i.e., vigorous eruption of bubbles of superheated vapors from the solution. Bumping is a serious safety hazard as material can splash hot material out of a flask: onto your skin or onto a hot surface where it might ignite. Which of the following devices is used to control bumping when heating material in the laboratory.

T: Boiling stones F: Micro Spatula T: Spin vane T: Boiling chips

Heating mantles are heating devices used in the lab to safely heat flammable organic materials in a round bottom flask. Which of the following statements about heating mantles are TRUE?

T: Heating mantles are used in conjunction with a voltage regulating time (time cycling) control T: For efficient heat distribution, heating mantles are mostly designed for specific flask size T: The heating element of a heating mantle has appropriate insulation from the flask which helps to prevent extreme temperature gradients F: Heating mantles responds quickly to changes in the control setting therefore allows for drastic inclines and declines of operating temperatures during the experiment.

A reflux setup allows for heating a chemical reaction for a given amount of time, while continually condensing the vapors produced back into the original flask using a condenser. Which of the following statements are TRUE/FALSE about reflux technique as applied in an organic chemistry laboratory

T: In a reflux setup, solvent vapors are trapped by the condenser, and the concentration of reactants remains constant throughout the process. F: When the reflux is done, the heat source and water flowing are immediately turned off and the contents in the round bottom flask are quickly poured into a second flask for air cooling T: allows for facile heating of a solution without the loss of solvent that would otherwise result from heating in an open vessel. T: Since refluxing involves heating material - mostly to solvent's boiling temperature - one should add appropriate smooth boiling devices to control bumping. False: If you are to reflux a reaction for a certain time period (e.g., "reflux for 45 minutes"), the time period should begin from when the heat source is turned on.

Hotplates are among the most versatile heat sources in the laboratory and are used to heat material contained in beakers, Erlenmeyer flasks, as well as heating various hot baths - water, sand, and oil baths. Which of the following considerations are TRUE/FALSE as it pertains to use of a hotplate in the laboratory

T: Volatile organic solvents should never be heated in an open vessel with a hotplate as the hot surface can reach very high temperatures and get hot enough to ignite the low boiling solvents T: You should never place an empty flask on the hot surface or heat a flask to dryness on a hotplate as this would result in glass shattering and potential injury in the lab F: If a hotplate surface becomes too hot one should return the heat control dial to the lowest heat setting and spray some chilled water on the surface for quick cooling T: Reactions that involve heating using a hotplate should be set up in the fume hood and the sash of the hood closed to isolate the reaction F: When removing a hot flask, such as an Erlenmeyer flask, off the hot surface one can quickly grab it by its neck using the tips of the fingers and place it on the bench top.

In chromatographic separations, components are partitioned between a mobile phase and a stationary phase based on differences in their partition (distribution) coefficients. Which of the following statement best define what a partition (distribution) coefficient is

The equilibrium ratio of the concentrations of a given component in two phases at a particular temperature.

Pure benzoic acid melts at 121-122 °C. These melting point tubes contain samples of benzoic acid at a temperature of 119°C. Which tube, A, B, or C is the purest sample of benzoic acid?

The one w/ the most produce in it

Suppose you have a 1:1:1 by weight mixture of three solid compounds, salicylic acid + 4-nitroaniline + naphthalene. You dissolve 1 gram of this mixture in diethyl ether, and spot the solution on a TLC plate. After the plate is developed, you see three spots. You then extract the ether solution with aqueous base and once again place a tiny drop of the ether solution on a TLC plate. Which spot(s) would disappear?

The spot with the second largest Rf value would disappear

Which of the following statements below describes how vacuum/suction filtration will be applied in the acid/base extraction experiment?

To separate solid precipitate from liquid part of the cold solution.

A filter paper is placed in the developing jar to ensure that solvent equilibration within the chamber is maintained.

True

Chromatography techniques are based on the differential partitioning of components between a stationary phase and mobile phase.

True

In thin-layer chromatography (TLC) the mobile phase travels up the TLC plate - adsorbent layer coated onto an appropriate support- by capillary action carrying with it the solute spot

True

TLC analysis requires microgram quantities of sample for an effective analysis. Spotting too much sample or having too broad a sample spot on the plate causes streaking which compromises the accuracy of your analysis

True

What statements are true of colligative properties?

True: Examples are freezing point depression, boiling point elevation, and osmotic pressure.False: Solution properties depend on identity not on the concentration of solute particles.True: Solution properties that depend on concentration not on the identity of solute particles.False: Examples are colour, taste and odour.

In thin-layer chromatography (TLC) the choice of visualization technique is dependent on the compound being analyzed. Which of the below-listed visualization techniques would be appropriate for visualizing benzaldehyde on a TLC plate?

True: Phosphomolybdic Acid (PMA)True: UV LightTrue: 2,4 dinitro phenylhydrazineFalse: Bromocresol GreenFalse: Iron (III) ChlorideFalse: NinhydrinTrue: Potassium permanganate ink/stain

Which of the following consideration are applied when choosing a suitable recrystallization solvent?

True: Should be unreactive toward the compound of interest.True: Does not dissolve impurity at all or complete/high solubility of impurity at all temperatures.True: Should have a boiling point that is ~ 30-40 ℃ above room temperature.False: Offers moderate solubility of the compound to be purified at room and lower temperatures.True: Dissolve the compound in a reasonable amount of solvent.

Clean glassware is essential for good and reliable results in the organic chemistry laboratories. Which of the following statements about cleaning and drying laboratory glassware are TRUE/FALSE.

True: Standard practice as far as cleaning glassware in the lab involves a preliminary wash using warm water, detergent and brush followed by final rinse with a few mL of distilled water before drying.True: Cleaned [wet] glassware should be dried thoroughly by open-air draining, towel or oven before using it to set up a reaction as residual water might be unfavorable to the reaction of interest.True: Organic residues that cannot be removed by detergent and water can be cleaned by rinsing with an organic solvent - i.e., technical grade acetone - that easily dissolves most organic compounds.True: Dirty glassware should always be cleaned at the end of each lab period or as soon as one is done using the glassware.

In a synthesis experiment you obtain a sample of product on which you do a melting point determination and find a melting point range of 108.0 to 114.3 degrees Celsius. The sample is supposed to be benzoic acid. What preliminary conclusion(s) can you reach from this one determination?

True: The melting point determination may need improvement -- it may not have been done properly, and make sure it was repeated at least once.True: The sample is probably impure.True: The sample may be benzoic acid.True: The sample probably needs recrystallization.False: The sample is not benzoic acid.

Which of the following are TRUE / FALSE concerning the appropriate use of a separatory funnel?

True: The stopcock of the separatory funnel should be effectively fastened before using the separatory funnel to prevent leaks.True: When venting you should point the tip of the separatory funnel away from yourself and others.True: You should vent the separatory funnel frequently while routinely shaking.True: While waiting for the layers to separate the stopper should be removed to prevent pressure build in the separatory funnel.True: The top layer (the liquid that remains in the separatory when the bottom layer is drained out] is collected by pouring it out of the top of the separatory funnel into a labelled container.False: You should shake the separatory funnel as hard as possible.False: The liquid contents can be filled to the brim as long as the separatory funnel can contain it.

Which of the below statements IS TRUE/FALSE concerning hot gravity filtration as applied in recrystallization experiment?

True: To prevent premature recrystallization, you should use at least 10-30% more recrystallization solvent than the minimum needed to dissolve the crude solid.True: Hot gravity filtration is applied to separate(remove) undissolved impurities from the hot solution.False: To minimize premature recrystallization during filtration the solution is poured rapidly into the funnel to rise above the top of the filter paper.True: If a few crystals form on the filter paper during filtration they can be dissolved by pouring a small amount of hot recrystallization solvent over them.

In a recrystallization experiment, colored impurity in the hot solution of crude sample is removed by adding activated charcoal (Norit). Which of the following are TRUE/FASLE about the process?

True: You should avoid adding too much Norit as excess can adsorb your product resulting in low recovery.True: The recrystallization solution should be kept hot enough throughout the process to prevent your product from crystallizing.False: Norit is separated from the hot solution using vaccum(suction) filtration on a Buchner funnel.True: Ideally, for standard scale experiments, Norit should be added in increments of 100 mg per cycle.True: You should let the boiling recrystallization solution cool down for approximately 1 minute before adding Norit.

In the space provided below calculate and record the Rf values of the observed spots of the unknown analgesic extract on plate #2.

Unknown #4: Solute Distance = 2.54 cm , Solvent Distance = 8.10 cm Rf= Solute Distance / Solvent Distance = 2.54 cm / 8.10 cm = 0.314

Chromatography is a term describing a collection of laboratory techniques used to separate the components in a mixture PRIOR to the measuring their individual responses for quantitative analysis. What chromatographic technique will be used to separate the volatile impurities in the unknown whiskey products.

gas chromatography

Suppose that a mixture of benzoic acid and p-nitroaniline is dissolved in ether. If the ether solution is extracted with aqueous 10% sodium hydroxide, which compound(s) would remain largely in the ether layer?

p-Nitroaniline would remain in the ether solution.

Which of the following does not represent a physical property?

reaction with oxygen