Orgo Lab Midterm

Cooling (Precipitation)

- The solution is cooled and precipitation is observed. Slower cooling yields crystals that are larger and higher purity. Solutions can be cooled below room temperature (e.g., in an ice bath at 0 °C) to further decrease the solubility of the desired solid (thereby increasing the precipitate).

Gas chromatography is an analytical technique that can efficiently separate mixtures based on

- answer: polarity -density -melting point -viscosity -"Polarity was discussed in the lab manuscript as well as the video introduction. None of the other variables was mentioned"

During extractions, it is common to add a dessicant/drying agent (such as magnesium sulfate) to absorb trace amounts of water from the organic layer (e.g., dichloromethane). If you were adding magnesium sulfate to 50 mL of dichloromethane in a 100 mL flask, how much MgSO4 should you add?

-1.0 g -0.5 g -the smallest amount possible (just enough to be visible) enough to fill the flask halfway -A: The correct amount is determined by observation. MgSO4 is added until the drying agent no longer clumps and there is no visible water floating on the surface

Atoms increase in size going down the periodic table; therefore, it is somewhat odd that iodine has a much lower energy cost than chlorine. Using your data above, propose a structural feature of the molecule that explains this result. (Limit your answer to 10 words or less)

-2 cyclohexanes drawn above: one with axial up Cl (kcal/mol) and other with axial up I (.1655 kcal/mol) -Answer: C-I bond length eliminates most steric strain in iodocyclohexane.

Relationship between carboxyl groups, N.E, and Molecular Weight (MW)

-In the case of carboxylic acids that contain one carboxyl group (R-CO2H), the neutralization equivalent and the molecular weight are identical -For an acid containing more than one carboxyl group per molecule, the molecular weight is the N.E. multiplied by the number of carboxyl groups in the molecule

A homogeneous mixture of liquids A (MM = 146 g/mol) and B (MM = 168 g/mol), containing 50 mol % of each, was heated to its boiling point of 120 ºC. At this temperature, the vapor pressure of pure A is 1000 Torr and the vapor pressure of pure B is 500 Torr. What is the mole % of A in the vapor?

-33 mole % -50 mol % - answer: 67 mol % -100 mol % -let PsubA = vapor pressure of A in this mixture; XsubA = mol fraction of A in the mixture; PsubA° = vapor press of pure A -PsubA = XsubA PA° = (0.5)(1000 T) = 500 Torr -PsubB = XsubB PsubB° = (0.5)(500 T) = 250 Torr -So total pressure PT = PsubA + PsubB = 500 + 250 T = 750 T -XsubA in the vapor = PsubA/PsubT = 500/750 = 0.67 or 67 mol %

Distillation safety notes

-A distillation must always be stopped before the flask becomes completely dry. Without the absorption of heat due to vaporization, the flask temperature can rise very rapidly -There is a risk of burning yourself today as the heating block and beads, along with part of your apparatus, will be very hot. -Also ensure that you lower the heating block after the distillation is complete so that the boiling flask does not go dry. -Discard the mixture and the distillate in the provided labeled container, *not the sink*. -there are certain cmpnds/liquids that very slowly decompose/ form peroxides (single sigma sigma bond) a) "explosive/ not stable- pretty high boiling" b) "liquids will get boiled off and peroxides wont get concentrated explosive peroxide & very high +" (?, see notes video?)

1. According to the label, the commercial glass cleaner Windex contains 8 ingredients; however, upon GC analysis only 7 compounds could be identified. Sodium dodecylbenzene sulfonate could not be located in the chromatogram. Why might this be the case?

-A) The sodium dodecylbenzene sulfonate evaporated before analysis could take place - "Not at all likely for a salt." -B) The sodium dodecylbenzene sulfonate has a very high boiling point -C) The sodium dodecylbenzene sulfonate elutes at the same exact time as another component of the mixture -Answers A & B -Answers A & C - Answer: Answers B & C -Answers A, B, & C -"Answers B & C are both possible, but since sodium dodecylbenzene is a salt, it may well not vaporize and go through the column with another component."

Suppose you have a mixture of copper sulfate (CuSO4) and azulene (C10H8). Both copper sulfate and azulene are beautiful deep blue crystalline solids. If you transferred the mixture to a separatory funnel containing both an aqueous and and organic solvents (1M HCl and dichloromethane), into which layer would the copper sulfate partition, aqueous or organic?

-A: Aqueous layer (1M HCl) -Organic layer (dichloromethane) -Copper sulfate would partition nearly equally into both the aqueous and organic layers

An unknown sample of nail polish remover contains a mixture of acetone and ethyl acetate. If the mixture is subjected to gas chromatography, which compound would have a longer retention time?

-Acetone - answer: Ethyl acetate (Acetone has a lower boiling point than ethyl acetate. Boiling point is a significant factor as mentioned in the video and manuscript. -Acetone and ethyl acetate would have the same retention time -Cannot be determined

Structural data: cyclohexane, benzene

-C-C Bond Length (nearest hundredth, angstroms) 1.536 1.342 -C-H Bond Length (nearest hundredth, angstroms) 1.116 1.103 -C-C-C Angle (nearest tenth) 110.9 120.0 -H-C-C Angle (nearest tenth) 109.9 120.0 109.4 (second cyclohexane value. first is first. first benzene is second) -H-C-H Angle (nearest tenth) 107.1 (n/a for benzene) -C-C-C-C Dihedral Angle (nearest tenth) 56.3 0.0 H-C-C-H -Dihedral Angles (nearest tenth) 174.6 0.0 57.2 60.2 (0.0 is the only benzene values; rest are cyclohexane) -Hybridization of carbon sp3 sp2

Structural data values of substituent CH3 (X) on cyclohexane in equatorial and axial positions

-C-X Bond Length (nearest hundredth) 1.54 1.54 -X-C-C Bond Angle (nearest tenth) 111.0 112.3 -X-C-H Bond Angle (nearest tenth) 108.0 106.2 -X-C-C-C Dihedral Angle (nearest tenth) 179.4 72.6 -Number of 1,3-Diaxial Interactions (Gauche interactions) Between X and Axial Hydrogens 0 2

Carboxylic acid lab safety review

-Common hazards: hot glassware, open flames, hot water bath, the surface of the hot plate and Mel-Temp apparatus. Be aware and use caution to avoid burns (thermal gloves available, if necessary). -Broken glassware. Handle with care and dispose of all broken glassware in glass waste receptacles. Wash hands if you touch or are exposed to your unknown carboxylic acid or other chemicals used during the chemical tests.

Distillation apparatus use important note

-Distillation is a potentially dangerous operation filled with a variety of hazards. DO NOT TURN ON YOUR APPARATUS until it has been checked by your instructor or teaching assistant. -Make sure to leave room for the heating block, hot plate, and lab jack. Also make sure to assemble your apparatus close to one of the sinks in the hood. (bolded in procedure). (implications?)

Etraction and acid/base chemistry

-Extractions can also be based on acid-base chemistry. the acidic and basic functional groups within a molecule can undergo acid/base chemistry and vastly alter which phase, organic or aqueous, into which a molecule or ion will partition. Being able to determine which layer a compound will partition into (e.g., organic or aqueous solution) is a key skill in organic chemistry. -benzoic acid and sodium benzoate (carboxylate anion) example: a)benzoic acid (1) is preferentially soluble in organic solvents and would favorably partition into the organic solvent (as compared to water). Benzoic acid also possesses an acidic carboxylic acid functional group (pKa 4) that can be deprotonated with base (e.g., NaOH, pKa(H2O) = 16). The proton transfer results in a charged (anionic) carboxylate salt, which would depart the organic phase and preferentially partition or locate into the basic aqueous layer -look up pic of rxn (manuscript #3 or google images)

Key aspects of extraction experiment

-Extractions rely on the differential solubility of particular compounds into two immiscible solvents. -In the idealized figure below, a mixture of molecules X and Y are dissolved in one solvent (A). After addition and mixing of a second immiscible solvent B, Y partitions preferentially into the upper (less dense) solvent A. Compound X partitions into the lower (more dense) solvent B.

Separatory funnel

-In practice, the separatory funnel (see picture) is used for extractions. One solvent is aqueous and the other is an organic solvent (most commonly diethyl ether, ethyl acetate, or dichloromethane). The shape of the separatory funnel is designed to permit draining of the lower layer through the bottom stopcock valve. -look up image

Recrystallization tools

-Mel temp: 3 slots for capillaries (and thermometer): determine MP -Hot plate: Heating

Which layer was the ether layer in the simulator?

-NB: ether is shorthand for diethyl ether (not sure what this means) -A: Top layer (ether has a density of 0.7 g/mL) -Bottom layer (water d=1.0 g/mL)

. A 2M NaOH aqueous solution and dichloromethane are combined and mixed in a separatory funnel. After allowing the layers to separate, which layer would be on top?

-Organic Layer -A: Aqueous Layer -No layers would form (miscible solvents) -No one could possibly predict such things

How would the resolution (separation into discrete peaks) be affected if you used a column that was half as long?

-Resolution would be better - Answer: Resolution would be worse -Resolution would not change -Manuscript justification: "Raising the oven temperature, increasing the flow rate of the mobile phase, and decreasing the column length will all reduce the retention time for each component as well as decrease the separation between peaks (resolution)."

Energy values of strain of substituent CH3 on cyclohexane in equatorial and axial positions

-Stretching Strain 0.45 0.48 -Bending Strain 0.47 0.96 -Stretch-Bend Strain 0.11 0.14 -Torsional Strain 2.14 3.10 -Non-1,4 VDW Strain -1.47 -1.35 -1,4-VDW Strain 5.20 5.33 -Total Energy 6.89 8.66 *VDW Strain?? (look up)

Cyclohexane, Benzene Strain Values (nearest hundredth: kcal/mol)

-Stretching Strain: 0.3330 0.1381 -Bending Strain: 0.3598 0.0000 -Stretch-Bend Strain: 0.0873 0.0000 -Torsional Strain: 2.1557 -5.5800 -Non-1,4 VDW Strain: -1.0636 -0.4023 -1,4-VDW Strain: 4.6841 5.2701 -Total Energy: 6.5564 -0.5741

Obtain following data: 1)Melting point range: 180-192 o C 2) The two trials for neutralization equivalent: 135 and 154 3) All three chemical tests (for S, N, and X): No precipitate Given this data, what should you do ?

-Take the melting point again because it is too broad AND repeat the titration as there is a large deviation in neutralization equivalent values -Explanation: it is completely fine for all the chemical tests to be negative. Many of the carboxylic acids on the list do not contain any Halogens, Nitrogen or Sulfur.

Gas Chromatography: safety review

-The biggest hazard today is from the sharp syringe needle. Take care that you do not stab yourself or a neighbor. Never carry or hold a syringe so that the needle could accidentally stab you or someone else. -The injection port of the GC is very hot so take care not to burn yourself.

1. What would happen to the retention time of a given compound if the carrier gas flow rate of the gas chromatograph is increased?

-The retention time would increase. - Answer: The retention time would decrease. -The retention time would not change. -manuscript justification: "Raising the oven temperature, increasing the flow rate of the mobile phase, and decreasing the column length will all reduce the retention time for each component as well as decrease the separation between peaks (resolution)."

You are subjecting a sample to gas chromatography and the resulting chromatogram shows no peaks. What has likely happened and what course of action would you take?

-The syringe is clogged. Check the syringe. -The LabQuest2 is not properly connected. Verify its connection. -The sample was injected into the wrong port. Review which port is specified for injection. -Sample was incorrectly injected. Review injection procedure, ensuring complete insertion through septum. -Answer: These are all likely scenarios that would result in no data acquisition. Review all potential issues and repeat injection and data collection and/or consult TA or professor.

Characteristics of Trans-1,2-dimethylcyclohexane (both methyls equitorial, both methyls axial)

-Total Energy (nearest hundredth, kcal/mol) 8.4577 10.8799 -Number of axial methyls 0 2 -Number of equatorial methyls 2 0 -CH3-C-C-CH3 dihedral angle 59.1 159.5 -Difference in strain energy between chairs A & B 2.42 -Number of 1,3-Diaxial Interactions (ring - substituent gauche interactions) 0 4 -Number of Gauche Interactions Between Methyls on Adjacent Carbons (substituent - substituent gauche interactions) 1 0 -Total Number Gauche Interactions 1 4 -Predicted Difference in Total Energy Based on 0.9 kcal/mol (per gauche interaction) Increment 2.7 -Difference in Total Energy Between Chairs A & B (from bottom of last page) 2.42 -Calculate Keq at 25 °C based on the difference in strain energy. Assume that strain energy is 𝐾eq = 𝑒 ^(-∆H/RT) where R = 1.987 x 10-3 kcal / K*mol 0.017 or 60 a) use 2.42 for delta H; T must be in K

Neutralization equivalent (N.E) in Carboxylic lab

-an important property that can be used to help identify carboxylic acids -Because the carboxylic acid functional group is acidic, a titration can be performed to neutralize this acidic functional group def:is the weight in grams of pure acid neutralized by one mole (40.0 g) of sodium hydroxide -in practice, (bc N.E. is identical), we determine how many millimoles of NaOH are required to neutralize a known milligram amount of acid -sample is weight and titrated with standard base solution. (known conc is usually about 0.1M)

Types of strain covered in orgo

-angle strain: discrepancy between ideal vsepr angle and actual angle -torsional (eclipsed) strain -steric strain: (aka nonbonded interaction):when atoms separated by 4 or more bonds are foced into contact closer than atomic radii allow (gauche is an ex) A) types of gauche interactions: 1,3 diaxial interactions (ring-substituent gauche interactions); substituents on Adjacent Carbons (substituent - substituent gauche interactions)

gc notes: factors that may affect recording of values

-different instruments might have slightly different columns a) "retention time is function of a molecule as well as the particular instrument you're using" -temp might affect it -"length" (?)

Extration notes

-experimental based lab -very common in orgo 2 -keytone has 2 C's and aldehyde has 1 -layer between upper and lower layers in separatory funnel: "interface" -put nothing down the sink (org cmpnds) -" if given any 2 or 3 cmpnds, u should know whether it's possible to separate them using extraction and should be able to articulate the process" -non halogenated solvents are less dense than water (?) -extraction- get 2 like things to separate by putting in aqueous soln and another substance that 1 of things is insoluable in and put in separatory funnell a) if no solubility diff, u can do some A/B rxns

Identification of carboxylic acid steps

-get pure substance. -Physical properties are used to help identify an unknown compound include (to name a few) melting and boiling points, solubility, color, odor, refractive index, and density -3 classical analytic techniques to identify unknown acid provided a table of possible selections: melting point, neutralization equivalent (a titration), and sodium fusion and three subsequent chemical tests (elemental analysis). -also spectroscopy but not really discussed right now

If you spill any acid or base on your skin, you should ________

-simply wipe it off with a paper towel -A: rinse your skin in the sink with copious amounts of water -not worry about it because we wouldn't give you dangerous chemicals to work with -neutralize the acid with concentrated sodium hydroxide

Melting point

-temperature at which the solid and liquid phases of that substance are in equilibrium at standard pressure (1 atm). -The melting point is a physical property of a substance that can be used to identify a compound (for example, the mp of water is 0 °C) and qualitatively assess the purity of a compound relative to a known sample of high purity -In a more general sense, an impurity in a given sample will have two effects on the melting point: (1) it will lower the melting point and (2) it can broaden the temperature range in which the substance melts.

Distillation: relationship between composition of a boiling liquid and composition of vapor of boiling water

-the composition of a boiling liquid is generally *not equal* to the composition of the vapor above the boiling liquid -view figure 1 in the manuscript or google boiling point diagram to familiarize with how to determine percent composition of distillate components at each stage of heating (or see notes)

gas chromatography: mobile phase

-usually an inert gas such as helium. Samples are injected into an injection block where they are immediately vaporized and carried into the column by the carrier gas. After passing through the length of the column, the now separated compounds are observed by a detector and recorded as peaks on a chromatogram. Individual peaks are described by their retention times (the time interval between sample injection and the maximum of the peak in question). -Raising the oven temperature, increasing the flow rate of the mobile phase, and decreasing the column length will all reduce the retention time for each component as well as decrease the separation between peaks (resolution).

Recrystallization cooling

-whatever around it can get trapped inside crystals -cooling slower and doing on the first time is better for purity

gas chromatography: finding approximate percentages of relative presence of compounds in a tested mixture

-𝑎𝑝𝑝𝑟𝑜𝑥𝑖𝑚𝑎𝑡𝑒 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 = (𝑎𝑟𝑒𝑎 𝑜𝑓 𝑝𝑒𝑎𝑘 𝑖𝑛 𝑞𝑢𝑒𝑠𝑡𝑖𝑜𝑛) / (𝑠𝑢𝑚 𝑜𝑓 𝑎𝑟𝑒𝑎𝑠 𝑜𝑓 𝑎𝑙𝑙 𝑝𝑒𝑎𝑘s) -area of peaks: w sub (1/2 h) * h -"area is proportional to amount"

The molecular weight of acetanilide is 135.17 grams/mole. The solubility of acetanilide in water is 5.5 grams/100 mL at 100°C and 0.53 grams/100 mL at 0°C. You are given a 30.0 gram sample of acetanilide that has been contaminated with insoluble sawdust. For every 10.0 grams of sample, 1.5 grams of that sample is sawdust. Theoretically, if you use just enough water to dissolve the entire sample of acetanilide, how much acetanilide will crystallize upon cooling to 0°C?

23.0 grams 1. If 1.5 g out of every 10 g is sawdust, then 4.5 g of the 30 g sample is sawdust and 25.5 g (30 - 4.5 g) is acetanilide. 2. Given that the solubility of acetanilide is 5.5 g/100 mL at high temperature, set up a proportion to determine how much solvent you'll need to dissolve all 25.5 g of sample (25.5 g/X mL = 5.5 g/100 mL). Answer = 464 mL 3. Now determine how much acetanilide remains dissolved upon cooling, again using a proportion. Recall that the solubility of acetanilide is 0.53 g/100 mL at 0°C. Working through this proportion (0.53 g/100 mL = X g/464 mL) reveals that 2.5 g of acetanilide will remain dissolved when the sample is cooled. 4. If 2.5 g of acetanilide remains dissolved, then the amount that will crystalize out is 25.5 g (our original amount from step 1) - 2.5 g = 23.0 g.

Select the most appropriate value that best corresponds to the neutralization equivalent of tartaric acid. (MW 150.09. Chem formula: C4H6O6) look up image*

75. Tartaric acid is a di-carboxylic acid, meaning it has two carboxylic acid functions. (The two -OH groups on a wedge at the center of the molecule are alcohol functional groups and not carboxylic acids!) For a di-carboxylic acid the NE is half the MW, so 150 / 2 = 75.

Given the following types of funnels (A-D), select the answer that correctly describes the set.

A separatory funnel B liquid funnel (narrow stem) C Buchner funnel D (for vacuum filtration) powder funnel (wide stem) -look up images

Filtration (Vacuum Filtration / Collection of Crystals)

A vacuum filtration setup will be used in your filtration for lab (Figure 3). A Büchner funnel, a filter flask, and a trap are used to collect the solid. After the solid is filtered and collected, the crystals can be washed/rinsed. The use of a vacuum allows a chemist to increase the rate of filtration. Filter paper of the correct size is fit into the Büchner funnel, which is then placed on top of a side-armed flask using a small grey neoprene rubber adapter to ensure a tight seal. The side-arm flask is then connected to a trap, which protects the vacuum line from solvent. Finally, the trap is connected to the house vacuum line in the hood. While the crystals are still in the Büchner funnel, they can be washed with ice-cold solvent to remove any soluble impurities that might remain. Cold solvent will help avoid dissolving the desired solid and lowering your yield. Once the crystals have been washed, the vacuum should be left on for a few minutes to pull air through the sample and help it dry.

Refer to P.6 in carboxylic acid manuscript -Sulfide ion test: negative -Cyanide ion test: negative -Halogen test: positive, white precipitate -MP range: 151 - 155 °C -Titration of 0.200 g acid (two titrations, volume of 0.1000 M NaOH necessary to reach endpoint): 12.5 mL, 13.2 mL

A: 3-chlorobenzoic acid Rationale: - contains X ion (a halide) and the precipitate is white which indicates presence of Chlorine. Other halogens should not be eliminated just yet as the color can be a bit tricky with this halogen test. - There are several halogen containing acid in the ballpark of the given melting range. No firm decision can be made yet. - Let's look at the neutralization equivalent: NE = 0.200g /( 0.01285L x 0.1M) = 155.6 g/mol (Note that for mL of base used I used the average between the two titration results) - This MW matches the one for 3-chlorobenzoic acid quite well (156.57 g/mol).

Refer to P.6 in carboxylic acid manuscript -Sulfide ion test: negative -Cyanide ion test: positive -Halogen test: negative -MP range: 137 - 139 °C -Titration of 0.200 g acid (two titrations, volume of 0.1000 M NaOH necessary to reach endpoint): 12.2 mL, 12.5 mL

A: 3-nitrobenzoic acid Rationale: - contains CN ion (cyanide) which indicates presence of Nitrogen - The only Nitrogen containing acid in the ballpark of the given melting range is 3-Nitrobenzoic acid. - Let's confirm with the neutralization equivalent: NE = 0.200g /( 0.01235L x 0.1M) = 161.9 g/mol (Note that for mL of base used I used the average between the two titration results) - This MW also matches the one for 3-nitrobenzoic acid the best (167.12 g/mol). Note that it is difficult to get the perfect MW as the titration is very sensitive. That's why the identification can't be made on the basis of a single test.

Suppose that you have a 1:1 mixture of compounds that is comprised of compound X and compound Y. You desire pure compound X and are planning a recrystallization to enhance the purity. Which solvent below is optimal for your recrystallization?

A: Ethyl Acetate (boiling point = 77 °C) Solubility At 0 °C 77 °C Cmpd X 0.10 g/mL 0.60 g/mL Cmpd Y 0.30 g/mL 0.60 g/mL In ethyl acetate, compound X has a wide solubility range between 0 and 77 °C. Also, compound Y is more soluble than compound X at 0 °C. These characteristics mean that you will be able to dissolve both X and Y at high temperature and then are likely to obtain crystals of pure X when the solution is cooled to °C.

Refer to P.6 in carboxylic acid manuscript -Sulfide ion test: negative -Cyanide ion test: negative -Halogen test: negative -MP range: 94 - 96 °C -Titration of 0.200 g acid (two titrations, volume of 0.1000 M NaOH necessary to reach endpoint): 13.2 mL, 13.3 mL

A: o-anisic acid (also known as 2-methoxybenzoic acid) Rationale: - contains none of the ions, which means this acid only contains C, H and O. - The are several acids that contain C, H and O only in the given melting range (remember impurities lower the melting range). So at this point o-anisic (2-methoxybenzoic) (98-100 °C), 3,3-dimethylglutaric (100- 102 °C) and o-toluic (2-methylbenzoic) (103-105 °C) should be considered. - Let's look at the neutralization equivalent: NE = 0.200g /( 0.01325L x 0.1M) = 150.9 g/mol (Note that for mL of base used I used the average between the two titration results) - From the three probable candidates this MW matches the one for o-anisic acid the best (152.15 g/mol).

Refer to P.6 in carboxylic acid manuscript -Sulfide ion test: negative -Cyanide ion test: negative -Halogen test: negative -MP range: 179 - 182 °C -Titration of 0.200 g acid (two titrations, volume of 0.1000 M NaOH necessary to reach endpoint): 33.7 mL, 33.7 mL

A: succinic acid (also known as butanedioic acid) Rationale: - contains none of the ions, which means this acid only contains C, H and O. - The are several acids that contain C, H and O only in the given melting range (remember impurities lower the melting range). So at this point p-toluic (4-methylbenzoic) (182-185°C), p-anisic (4- methoxybenzoic)(182-185 °C) and succinic (butanedioic) (187-190 °C) should be considered. - NE = 0.200g /( 0.0337L x 0.1M) = 59.3 g/mol but this MW is far too low and does not match any of the potential candidates. One of the options, succinic acid, is a dicarboxylic acid. Therefore the MW is double the NE so 118.6 g/mol (Note that for mL of base used I used the average between the two titration results) - This MW matches the one for succinic acid the best (118.09 g/mol)

Solvent selection in recrystallization

An ideal solvent for recrystallization would see the desired solid highly soluble at high temperature but sparingly soluble at low temperature. The boiling point of the solvent must be high enough to give ample range for heating. Volatile solvents such as ether (b.p. = 35 °C), pentane (b.p. = 35 °C), and methylene chloride (aka dichloromethane, b.p. = 40 °C) do not work well. Alternatively, the boiling point of the solvent should not be too high, which slows the necessary evaporation of any remaining solvent to give the pure solid. Overall, a temperature range between 50 and 80 °C is generally desirable.

gas chromatography: qualitatively confirming identity of peaks

Any new peak that appears (in sample in graph chromatograph) in relation to your unknown sample indicates that compound is not present in your unknown; furthermore, an increase in the relative size of a peak present in your unknown identifies that compound as a component in the original unknown mixture.

Extraction lab safety review

Both the 6M HCl and 3M NaOH used in this lab are caustic compounds! If you spill some on your skin, rinse the exposed area with copious amounts of water. Additionally, if you are uncertain of your ability to pour and transfer these aqueous solutions without exposure to your skin, you can wear disposable gloves which are located on the shelf above the dispensing bench. As always, be aware and wear goggles at all times.

Impurities affect BP by:

Broadening and lowering MP range

A Buchner funnel resting on top of a filtration flask is very top heavy and easily knocked over. What is the one guaranteed way to avoid knocking the apparatus over?

Clamp the filtration flask. ALWAYS!

Recrystallization lab safety review

Common hazards - Burns (hot glassware and hot plates) and cuts (from broken glassware) Manipulate hot glassware with caution (thermal gloves available if necessary). Don't touch hotplates or the metal parts of Mel-temp® apparatus. Wash hands if you touch or are exposed to acetanilide.

Compound A has a melting point range of 78-80 °C and compound B has a melting point range of 80-82 °C. An unknown compound X is found to have a melting point range of 79-81 °C. Compound X and compound A are mixed together and mixed melting point analysis gives a range of 65-74 °C . Which of the following statements is definitely true?

Compound X is not compound A. The melting range of the X-A mixture was lower and broader than the melting range of pure A. This result tells us that X and A are different compounds.

Cost of each 1,3-diaxial interaction due to axial CH3 (X) on cyclohexane

Conformational energy of X / # Gauche interactions = 0.88 (1.77/2)

1. Using the attached chromatograms, please determine the identity of compounds in Unknown #3 and determine the percentage that each compound makes up of the unknown mixture. GC unknown #3 - All Chromatographs.pdf

Cyclohexane: Absent THF: Absent Toluene: Present 66% o-Xylene: Present 34%

1. Using the attached chromatograms, please determine the identity of compounds in Unknown #4 and determine the percentage that each compound makes up of the unknown mixture. GC unknown #4 - All Chromatographs.pdf

Cyclohexane: Present 13% THF: Present 49% Toluene: Present 38% o-Xylene: Absent

1. Using the attached chromatograms, please determine the identity of compounds in Unknown #1 and determine the percentage that each compound makes up of the unknown mixture. GC unknown #1 - All Chromatographs.pdf

Cyclohexane: Present 31% THF: Present 27% Toluene: Present 42% o-Xylene: Absent

Some organic solvents do not work well in liquid-liquid aqueous extractions. Ethanol (HOCH2CH3) is a common inexpensive solvent, but is a poor solvent for extractions. In ten or fewer words, provide an explanation for why ethanol is a poor solvent selection for extraction. Hint: you may want to look up various properties of the molecule

Ethanol is miscible with both water and organic solvents (such as ether or dichloromethane). Extraction requires immiscible solvents.

Chem lab food policy

False: -Drinking water is allowed in the lab as long as it is in a sealable container -Bananas are allowed in the lab since they are safely cradled within a peel. -You can probably get away with eating or drinking in the lab as long as you are careful. After all, how bad could organic waste be for you? True: -No food or drink of any kind is ever allowed in the lab

Extraction acid/base chemistry examp pseudoephendrine (an amine) and pseudoephendrine*HCl (ammonium salt)

For a complementary case, see the example with an amine (pseudoephedrine 3, eq 2). Pseudoephedrine (3), which possesses a basic amine functionality, would partition into an organic layer in preference to water. If, however, the pH is low (acidic environment), the amine would protonate to give the derived ammonium salt. This salt, being charged, would partition into the aqueous layer. -look up pic of rxn (manuscript #3 or google images)

Extraction acid/base chemistry example: fluorenone and Na+ w/ OH- or H+ and Cl-

In equation 3, fluorenone (2) has neither acidic nor basic functional groups, and thus it does not respond to treatment with either aqueous acid or base. Accordingly, 2 would partition into an organic solvent in preference to HCl in water (aqueous acid). Likewise, 2 would partition into the organic layer in preference to NaOH in water (aqueous base) -look up pic of rxn (manuscript #3 or google images)

Why would a solvent with a very high boiling point be inappropriate for a recrystallization

It would be difficult to remove residual solvent from the purified crystals The higher the solvent's boiling point, the harder it is to remove from the purified crystals. Use of such solvents necessitates long drying times and/or high heat in an oven to obtain dry crystals.

Next, complete a similar analysis for cis-1,2-dimethylcyclohexane. What is Keq for the two possible chair conformations? If necessary, use Chem 3D Pro to model the two structures. Concisely explain how you arrived at your answer.

Keq = 1; The two chairs are energetically identical

What if many different cmpnds have similar BPs and you want to find out what an unknown substance it

Mix them with a known substance that has a bp around that range. If it lowers and broadens (BP), its not it. If its really close/ doesn't change: same.

Instructions for washing your crystallized product in the vacuum filter funnel call for using the icecold wash solvent. Why is this important? How would the success of the experiment be affected if the wash solvent were warm?

More of the product will dissolve if the wash step is carried out with warm solvent. You can literally dissolve away your crystals by washing with hot solvent! Using ice cold solvent helps remove impurities without dissolving the crystals.

Hazards associated with sodium fusion operation

Open flame, Hot glassware, Highly reactive sodium metal, Potentially sharp broken glassware

Sodium Fusion and 3 Chemical Tests (Elemental analysis) in Carboxylic Acid Lab

Organic compounds frequently contain atoms other than C, H, and O. Some of these other atoms, specifically halogen (X), nitrogen (N), and sulfur (S) atoms, can be identified through classic chemical tests, however these atoms need to first be reduced to their inorganic salts. Fusion with a small amount of molten sodium metal, a very strong reducing agent, destroys the molecule (C, H, O are combusted) and converts sulfur to sulfide ion (S2- ), nitrogen to cyanide ion (CN − ) and halogen to halide ion (X − ). These ions are dissolved in water and qualitatively tested by three separate techniques. -presence of: a) S2^-: black b) CN^-: blue (prussian blue aka stary night blue) c) X^- (Halogen): Cl: White, Br (off white/pale yellow), I (bright yellow)

How to load the capillary tube for melting point analysis

Place a few milligrams of dry solid on a watch glass or on a filter paper. If needed, crush the sample with a spatula. Introduce the solid into the capillary tube by tapping the open end of the tube into the fine crystals. A small amount of solid will stick inside the top, open end tube. Invert the tube and tap the closed end against the bench. Usually, the solid falls to the bottom, closed end of the tube. If tapping fails to move the sample to the bottom of the tube, drop the capillary down a glass tube (5 to 8 mm diameter) resting on a hard surface bench (and/or see your TA or Professor for help). Wet solids are difficult to get to the bottom of the tube. Just as well, for the observed melting point of a wet solid is worthless

Melting point analysis

Purpose is to determine the identity of an unknown substance. -Melting point analysis is also considered part of the characterization of a new substance and can also be used in the organic lab to get an indication that the substance is both pure and dry

Extraction lab purpose

To separate a mixture of benzoic acid and fluorenone using extraction. Vacuum filtration and use of a rotovap are necessary components of the lab. Melting point analysis will be used to assess the purity (and identity) of the recovered materials.

Identical amounts of compound and solvent are used to perform two recrystallizations in the lab. After heating, Sample A is cooled slowly to room temperature and then placed in an ice bath for additional cooling. Sample B is placed in the freezer immediately after heating. Which sample will produce higher purity crystals?

Sample A: The faster the crystallization occurs, the less pure the crystals will be. Slow and steady is best!

In order to perform a vacuum filtration, three individual items are assembled by stacking them on top of each other and the overall apparatus is connected to a vacuum source. A clamp is attached to secure the entire setup.

TOP ITEM - MIDDLE ITEM - LOWER ITEM - ITEM ATTACHED TO CLAMP Buchner funnel-adapter-filter flask-clamp

How would you best describe the C-C bonds in benzene? Are they single bonds or double bonds?

The C-C bonds in benzene are between a single and double bond.

Rotovap

The Rotovap® (see diagram) is an essential and time-saving fixture in the organic lab that permits rapid removal of organic solvents. The main components are labelled in Figure 2. There are 2 Rotovaps® in each lab, in the corners near the windows. Prior to using, please consult the appendix for full details on operation, review the video tutorial on Blackboard, and/or ask your TA or Professor for assistance. If you are waiting to use the rotovap, observe the group before you and how they use the rotovap. Overall, a round bottom flask (rbf) containing your compound dissolved in dried organic solvent is fitted to the ground glass joint and secured using a clip. The Rotovap® contains a heat source (hot water bath) for faster evaporation, a vacuum attachment (to decrease the pressure and lower the boiling point), and a motor to spin the flask. The spinning operation both increases the surface area (which speeds up evaporation) and ensures even evaporation of solvent rather than 'bumping' and splattering. -look up image/diagram in Manuscript #3 or on google images

Dissolution of solid

To the organic solid is added the chosen solvent and the mixture is heated to its boiling point on a hot plate. Only enough solvent as necessary to fully dissolve the solid should be used to ensure efficient recovery (yield).

BP note in carboxylic acid lab

The melting point values listed in the table of acid unknowns are for pure samples of the acids. The commercially available acids distributed as unknowns may be slightly less pure (possibly 98% or even 95% pure). These impurities may result in a measured melting point slightly below the value listed in the table. -melting point of a pure substance is a constant physical property -You will determine the melting point of the unknown sample using the procedures outlined in the previous lab

1. You are monitoring the reaction A --> B via periodic GC analysis. Initially, you only see one peak in your chromatogram; however, over time you find that a new peak is growing while the original peak is shrinking. What is happening?

The reaction is proceeding

Why would a solvent with a very low boiling point be inappropriate for a recrystallization?

The solvent could not be heated to a high enough temperature for the target compound's solubility to change significantly -Figure 2 (EXPT 1) in the manuscript shows us that compound should have low solubility in the recrystallization solvent at low temperature and high solubility at high temperature. This transition from low to high solubility typically occurs gradually. A low-boiling solvent restricts the range of temperatures you can access during a recrystallization, limiting the efficacy of the technique

gas chromatography purpose

Today's experiment will use gas chromatography to identify the compounds present in an unknown mixture as well as calculate the percentage present for each compound. You will "spike" samples of your unknown to confirm the identity of each peak.

Carboxylic acid lab purpose

To determine the identity of an unknown carboxylic acid. The ability to synthesize several pieces of data and select the carboxylic acid from the table that best fits your data is a key component of the lab. This lab exercise also reinforces several experimental techniques (melting point, titration, classic chemical tests).

Recrystallization lab purpose

Today's experiment will use recrystallization to obtain pure acetanilide from a mixture of impure of acetanilide and an unknown impurity. Melting point range will be used to identify recrystallized material and qualitatively determine its purity as compared to a standard sample of high purity

Conformational Energy for Substituent CH3 (X) on cyclohexane

Total Energy (Axial) minus Total Energy (Equatorial) = 1.77

Drying

Trace/residual solvent in the crystals must be removed by evaporation. Today, we will accomplish this both by pulling air over the crystals (during vacuum filtration for a few minutes) and by drying the sample in an oven for more complete evaporation of the solvent.

Lab Safety

True: -Broken glass should never be put into a trash can -Students must clean the bench top and hood with paper towels and water after each experiment. -All organic chemicals should be treated as if they are flammable and toxic False: -Students can safely assume that any organic waste they have produced can be put down the sink

Chem lab attire

True: -Shoes must be worn that cover the entire foot. -Lower body clothing must cover the entire leg. -Sweatpants are an appropriate form of legwear. False: -Upper body clothing must cover the entire arm.

Goggle safety

True: -Virginia State Law mandates that students in an academic laboratory must wear chemical splash goggles at all times. -If a student does not bring goggles, he or she may borrow a pair from the department. -Goggles should create a tight seal so that no splashed liquids can touch the eye. False: -Contact lenses are just as safe as glasses when they are worn within the organic chemistry laboratory.

The carefully worded instructions on using the sink handles in the experimental procedure should be followed closely. (T or F)

True: Otherwise we sometimes get water leaks in the wall of the hood, and that's no fun for anyone.

It's best to use as little hot solvent as necessary to fully dissolve the solute during a recrystallization. Why?

When too much solvent is used, the solute will remain dissolved, even when the solvent is cooled down (remember the analogy with the swimming pool: when the volume is too high, the solute will remain dissolved). When as little hot solvent as necessary is used, the solute will crystallize when the temperature is lowered

Extraction: how to isolate pure cmpnd after cmpnd of interest has been partitioned into the desired layer

While the particulars of this step can vary for each individual extraction, in general if the organic compound of interest is in an organic solvent, then the solvent is dried to remove trace water and the solvent is removed by evaporation (leaving only the desired compound). Since the organic layer was exposed to water, all solvents will saturate with a small amount of water. Ethyl acetate and ether (which absorb 4% and 8% water by weight) are most notorious in this regard. Chlorinated solvents like dicholormethane saturate with <1% water, but even this small amount, if not removed, complicates obtaining pure, dry product. Drying the organic layer is accomplished by adding an inorganic desiccant (which can subsequently be removed by gravity filtration, or in some cases decanted). Evaporation is performed using a rotary evaporator, which is more frequently called a Rotovap®

Following sodium fusion and fracture of the test tube into 15 mL of deionized water (in a 50 mL beaker), the next step is to ________.

Yes: Filter the solution to remove insoluble material and glass fragments No: Add phenolphthalein indicator and perform a titration, Perform the chemical test for formation of lead sulfide (PbS), Perform any of the three chemical tests for sulfur, nitrogen, or a halogen, Discard the solution into the sink and clean the beaker

Which hazards are associated with the sodium fusion operation

Yes: Open flame, Hot glassware, Highly reactive sodium metal, Potentially sharp broken glassware No: Strongly acidic solution (6 M H2SO4)

gas chromatography waste and cleanup

Your five samples should be poured into the container labeled "acetone rinsings" on the dispensing bench. Use the acetone to rinse the test tubes several times and return them to the test tube racks where you originally got them. Please put the rinsed unknown test tube in the rack for the unknowns.

gas chromatography: the stationary phase

a high boiling liquid or polymer suspended inside metal tubing (the column) in an oven.

Recrystallization

a method of purification (to increase the purity of a substance)

dihedral angle

angle connected by 2 intersecting 3-atom planes. more strain, more E, less stable (eclipsed strain>staggered)

determine whether the compound in question will partition into the organic or aqueous phase. (look at image in google images or manuscript 3) -quinine: (antimalarial compound and component of tonic water) -aqueous phase: 3M HCl -organic phase: dichloromethane

ans: aqueous phase: b/c protonation to ammonium salt in 3M HCl

determine whether the compound in question will partition into the organic or aqueous phase. (look at image in google images or manuscript 3) -naphthalene: (the classic constituent and characteristic odor of moth balls) -aqueous phase: 3M HCl -organic phase: ethyl acetate

ans: organic phase. naphthalene is an organic substrate, a hydrocarbon, and can not protonate (or deprotonate) in response to aqueous acid (or base)

determine whether the compound in question will partition into the organic or aqueous phase. (look at image in google images or manuscript 3) -nootkatone: (the primary characteristic odor of grapefruit) -aqueous phase: 3M NaOH -organic phase: dichloromethane

ans: organic phase. nootaktone is an organic substrate, a hydrocarbon, and can not protonate (or deprotonate) in response to aqueous acid (or base)

-determine whether the compound in question will partition into the organic or aqueous phase. (look at image in google images or manuscript 3) -phenylalanine (an essential amino acid * this is a tricky one) -aqueous phase: water -organic phase: diethyl ether

aqueous phase: water b/c amino acid exist as zwitterionic form. Internal acid/base equilibrium operational

If 80% of a desired compound is extracted into the organic phase in each step (leaving 20% in the aqueous layer), how many extractions are necessary to ensure that at least 99% of the compound has been recovered in the organic phase?

assuming equal volume of extraction solvents, 20% remains. After 3 extractions (answer), 0.8% remains in organic phase and 99.2% has been recovered: (0.2)(0.2)(0.2)=0.008x100=0.8% remaining. 100- 0.8=99.2%

distillation: thermometer placement

bulb must be below condenser to make sure to have accurate temp reading foe the gas

Distillation lab purpose

distill a mixture of cyclohexane and toluene and see how the composition of the distillate varies over time. We will use gas chromatography to determine the mole fraction of each component in the distillate.

Extraction lab techniques required

extraction; use of the separatory funnel and rotovap. Previously introduced techniques reinforced in this lab: vacuum filtration (with Büchner funnel); melting point analysis

Gas Chromatography Experimental Techniques Required

gas chromatography

In recrystallization and reaching close to MP

heat substance by around 2 deg C/ min. Takes a while to cool: get it right the first time. Start this at around 20 C below MP. before that do around 10-15 C/ minute

Recrystallization process

heat; dissolve. cool; precipitate product (1/2 cmpnds selectively crystalize). pour out of beaker into another with filter (vaccum is also there to suck moisture). collect crystals. most of one cmpnd remains in solvent while most of other remains in crystals. make second crop if necessary

fraction distillation

helps overcome the difficulties that come across a fairly simple distillation when BP is close

gas chromatography: relationship between a polar stationary phase and time spent in column by substances

in given lab: -"the column we are using has a polar stationary phase and we generally expect less polar (lower boiling) compounds to spend the least time in the column. However, addition of a polar functional group or heteroatom can affect this trend"

Chromatography

laboratory technique used to separate mixtures of compounds. All forms of chromatography depend on the separation of substances between a mobile phase such as a solvent, or in this case a gas, and a stationary phase. Compounds are separated due to a difference in affinities between the two phases. Compounds with a greater affinity for the stationary phase move more slowly through the apparatus while compounds with less affinity move more quickly. -look at figure 1 in manuscript or google block diagram of a chromatograph

distillation: "bombing"

little rocks go at bottom of round flask that contains the mixture. "bombing" (used in rotovap) -provides nucleation point for gas to form a) "instead of liquid randomly bumping and popping you get its if little bubbles- keeps system in check

Examples of daily extraction

making coffee or tea

Identification of an Unknown Carboxylic Acid Experimental techniques required:

melting point analysis, neutralization equivalent (titration), sodium fusion and subsequent chemical tests for sulfur, nitrogen, and halogen

reality of distillation

mixtures evaporated and not won't be 100% pure. however progressive trials can continue to increase degree of purity.

Summary of recrystallization process

purify substance, dry crystals, analyze using MP analysis: a) how much stuff is left in solution b) how much stuff is removed from the solution c) Crop 1 v crop 2, etc.

Recrystalization Experimental techniques required

recrystallization, vacuum filtration, melting point analysis (and qualitative analysis of purity and mixed melting point), yield calculation

A lower and/or broader melting point range for a compound after recrystallization most likely results from ________

the material still being wet with the recrystallization solvent

Homogeneous Distillation

the process of vaporizing a liquid into the gas phase and then condensing the vapor back to the liquid phase, collecting the distillate. If carried out properly, distillation separates substances with different boiling points (difference in BPs is required**). -"Just as recrystallization is routinely used for the purification of solids, distillation is usually the first choice for purification of liquid" -process used in real life: many hydrocarbons obtained by crude oil

Refer to P.6 in carboxylic acid manuscript -Sulfide ion test: positive -Cyanide ion test: negative -Halogen test: negative -MP range: 125 - 129 °C -Titration of 0.200 g acid (two titrations, volume of 0.1000 M NaOH necessary to reach endpoint): 26.2 mL, 25.9 mL

thiodiglycolic acid Rationale: - contains sulfur ("thio"). - impurities lower melting range so thiodiglycolic acid (128-131 °C) and 3,3'-thiodipropionic (131-134 °C) should be considered at this point. - NE = 0.200g /( 0.02605L x 0.1M) = 76.8 g/mol but since both options are di-carboxylic acids the MW is double the NE so 153.6 g/mol (Note that for mL of base used I used the average between the two titration results) - This MW matches the one for thiodiglycolic acid the best (150.15 g/mol)

distillation: condenser

vapor of mixtures are condensed after evaporation. done in part connected that has tubes of cool water running around it to condense all the gas back into liquid

Melting point range

when substance begins and ends melting

According to the Distillation Theory Video, a 50/50 mixture of toluene/benzene would have what vapor mol % of benzene when it is heated to boiling?

• 0 mol% • 20 mol % • 50 mol % • answer: 80 mol % • 100 mol % The answer is worked out on the screen at the 3:23 mark of the video

. Which of the following statements is false?

• Azeotropes are mixtures of liquids that have a vapor that is proportional to the constituents of the liquids. • Answer: Azeotropes can be distilled using a fractional distillation. • Azeotropes have a lower boiling point than either constitutent of the mixture. • Ethanol and water are an example of an azeotrope. - explanation: Azeotropes cannot be separated using traditional simple and fractional distillation techniques.

Which piece of distillation glassware has a hollow section surrounded by a separated sleeve?

• Boiling flask • Distillation column • Three-way adapter • Answer: Distillation Condenser -explanation: The condenser is where vapor re-condenses to form liquid. It stays cool due to the water the flows through its sleeve.

Which of the following statements about the distillation of a cyclohexane/toluene mixture is false?

• Distillation separates liquids based on their boiling points. • Answer: If a 50 mL equal mixture of cyclohexane and toluene are distilled, the first 25 mL collected will be pure cyclohexane and the second 25 mL collected will be pure toluene. • The composition of distillate changes as the composition of the liquid mixture changes. • The first 25 mL collected will contain more cyclohexane than toluene. -Explanation: In practice, distillation is not as "clean" as the false choice above suggests. In reality, there will be more cyclohexane than toluene in the first 25 mL, but the distillate will not be 100% cyclohexane.

Where should the thermometer bulb be placed in a distillation apparatus?

• In the boiling flask • In the graduated cylinder receiving the distillate • Above the side arm connecting the column to the condenser • Below the side arm connecting the column to the condenser - Explanation: Incorrect thermometer placement is one of the most common errors in setting up a distillation apparatus. You will obtain incorrect information about the boiling points of your solvents if the thermometer is not correctly placed.

Which of the following statements are false? (This question is in reference to the specific distillation setup that William & Mary uses)

• Plenty of room should be left under your distillation apparatus for your lab jack, hot plate, and heating block. • Your distillation apparatus should be set up fairly close to the sink in your hood. • Your round-bottom flask should contain 3-5 boiling stones. • Answer: Your round-bottom flask should be only slightly submerged into the beads. • The cord of your temperature sensor and your hoses should be carefully draped on the monkey bars so that they do not touch the hot plate. • Make sure to use only a gentle flow of water in your condenser. • None of the answers above are false. - Explanation: The round-bottom flask should be roughly halfway submerged in the beads

There is an error in the apparatus setup for the "Distillation Setup Video (real life)". What is the error?

• The water-in and water-out tubes are connected backwards to the condenser. • The boiling flask is overfilled with the mixture to be separated. • The collection flash is not adequately clamped. • Answer: The thermometer bulb is not correctly placed below the side-arm of the three-way adapter. - Explanation: The very beginning of the video shows a closeup of the apparatus. The thermometer bulb is clearly NOT visible below the side arm connecting the column to the condenser. It is placed far too high in this setup. Remember, incorrect thermometer placement is one of the most common errors in the distillation setup - even in YouTube videos!

Once you have collected 40 mL of distillate, you should:

• turn off your hot plate • lower your lab jack carelessly • use your hand to remove the heating block • answer: turn off the hot plate and carefully lower the lab jack, making sure that no cords or hoses get caught in it

neutralization equivalent equation

𝑁. 𝐸. = (𝑚𝑔 𝑜𝑓 𝑎𝑐𝑖𝑑)/ (𝑉𝑏𝑎𝑠𝑒,𝑚𝐿 × 𝑀𝑏𝑎𝑠𝑒) = (𝑚𝑔 𝑜𝑓 𝑎𝑐𝑖𝑑)/ (𝑚𝑚𝑜𝑙 𝑜𝑓 𝑏𝑎𝑠e)