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Experiments 4-7 (Lab)

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How many samples should you run in parallel?

3 - Positive, negative, and unknown

What is a good Rf value in order to ensure that a compound will elute over a reasonable timeframe?

Around 0.3 - Too low and the compound won't elute. Too high and it will run through the column too quickly.

Where should the thermometer bulb be during a distillation?

At the mouth of the condenser - The bulb should be at the mouth of the condenser to measure the temperature of the condensate

Look at #7 E7 Worksheet: Which structure best fits the above IR spectra?

Carbonyl: ketone, not benzaldehyde Alcohol: not carbonyl

Look at #13 E7 Practice Quiz:

Choose bonds and IR

State the objective of Part C for Experiment 4

Column chromatography: separation of the mixture using TLC: evaluation of the purity and components of the compounds

Which of the following is not a GHS hazard code for the Jones reagent (chromic acid solution)?

H303 - May be harmful if swallowed

Briefly state the objective of Experiment 5

Separate a mixture of hydrocarbon volatile liquids, through simple and fractional distillations - Evaluate their separation and identity with GC

If a student separated a mixture of 1-propanol, 1-butanol, and 1-pentanol by GC, what would be the expected order of retention times?

Shortest retention time: 1-propanol Middle retention time: 1-butanol Longest retention time: 1-pentanol

In silica gel chromatography, which compounds elute first?

The least polar - In silica gel chromatography, polar compounds are retained on the column, as they have a greater affinity for the silica than the more non-polar compounds that are eluted first.

What happens if the spots are added below the level of the solvent when preparing a TLC plate for development?

The spot material will dissolve off the plate. - If the spots are placed below the level of the solvent, they will dissolve off the plate and into the solvent.

SAFETY: When clamping the condenser in a distillation, avoid clamping it too tightly to prevent breaking the glass joints.

True - Only loosely clamp the condenser to avoid breaking any of the joints

Which of the following statements best describes the experimental objective of Part B in Experiment 4?

Determine the identity of an over-the-counter analgesic using TLC

Look at #3 E7 Worksheet

FLOWCHART

A student performed 3 boiling point determinations (using a fresh sample each time) and obtained the following bp for his unknown ester product in E6. Observed BP #1: 202C Observed BP #2: 183C Observed BP #3: 171C Using Table 1 in the Lab Manual Handout, select the best match for the unknown ester

Heptyl acetate

Rank the following solvents from most polar to least polar

Rank 1. Most polar -Isopropanol Rank 2: More polar - Ethyl acetate Rank 3: Less polar - Methylene chloride Rank 4: Least polar - Hexane/s

The stationary phase in TLC is the ________ which is ________. Therefore, the ________ component of a mixture will travel a longer distance up the plate, resulting in a ________ Rf value for the component.

Silica gel; polar; less polar; larger

Using a less polar solvent when running a TLC will result in nonpilar compounds migrating a greater distance up the plate because of ________ interactions between the nonpolar compounds and the stationary phase and ________ interactions between the nonpolar compound and the mobile phase

lesser; increase; decrease

Which of the following is a GHS hazard code for n-heptane?

H225 - Highly flammable liquid and vapor

Which of the following is a GHS hazard code for acetylsalicylic acid?

H302 - Harmful if swallowed

Which of the following is a GHS hazard code for 3,5-dinitrobenzoyl chloride?

H314 - Causes severe skin burns and eye damage

Which of the following is not a GHS hazard code for methanol?

H350 - May cause cancer

SAFETY: Which of the following statements about the procedure for column chromatography are true? More than one answer may be correct.

- Apply enough pressure to increase the flow rate to a reasonable degree. - Check for cracks in the glass before pressurising the system. - The column should not be over pressurised. Releasing the pressure suddenly can cause cracks in the column. The column should be securely clamped, but not too tightly so as to damage the column.

#16 - Look at E4 Worksheet: You want to purify two compounds using column chromatography. You first use TLC to test different solvents int he hopes of finding a solvent that responses the two compounds well. You test 3 solvents and obtain the following results. You have bottles of 1) diethyl ether 2) dichloromethane, and 3) toluene. Which did you use in each TLC? The best solvent that you should use to purify the 2 compounds by column chromatography is ________.

- Closest to top, close together: diethyl ether (H-bonding > polarity) - In the middle, far apart from each other: DCM - Closest to bottom, close together: toluene - Solvent B

Intermolecular interactions that occur as 3-methylbenzaldehyde proceeds up a Silica gel TLC plate with diethyl ether as the solvent

- Dipole-dipole interactions - Hydrogen bonds Stationary phase: silica gel (SiO2) Mobile phase: diethyl ether Compound: 3-methylbenzaldehyde

#22 - Look at E4 Worksheet: A student attempted to separate ferrocene, 9-fluorenone, and acetyl-ferrocene using column chromatography. After finishing the column, she obtained the following results by TLC analysis. Help her interpret the TLC results - determine the contents of each fraction and decide if the separation was successful.

- Fraction 1 contains: ferrocene & 9-fluorenone - Fraction 2 contains: 9-fluorenone & acetyl-ferrocene - The separation was not successful - no pure fractions were obtained (Different every case)

#10 - Look at E4 Worksheet: Using the TLC and ruler below, calculate the approximate Rf of the least polar compound

- Least polar compound traveled the most (11-1.5)/(13.4-1.5) = 0.8

SAFETY: Why is it important to handle silica powder in a fume cupboard?

- The powder is fine and easily inhaled. - The powder, if inhaled, can cause serious problems to the respiratory tract.

SAFETY: Why is it important to handle silica powder in a fume cupboard?

- The powder, if inhaled, can cause serious problems to the respiratory tract. - The powder is fine and easily inhaled.

Consider a sample that is a mixture of 3 components of different polarity. Predict the order of elution of the three components in this mixture. You are using a silica column and the solvent system is based on petroleum ether, with increasing MTBE added as a function of time.

- Toluene: Elutes first - Acetophenone: elutes second - Benzoic acid: elutes third

#8 - Look at E5 Worksheet: The thermometer bulb in set up A is _______. The temperature reading in set up A will be _______ The thermometer bulb in set up B is _______. The temperature reading in set up B will be _______ The thermometer bulb in set up C is _______. The temperature reading in set up C will be _______

- Too low; higher than the true condensation temperature - Too high; lower than the true condensation temperature - Just right; the true condensation temperature

Look at #13 on E4 Practice Quiz: What are the Rf values of the spots on this TLC plate?

0.19 and 0.42 - The Rf values of the spots on this TLC plate? value is calculated as the ratio of the distance travelled by the spot to the distance travelled by the solvent front.

Look at #18 on E5 Worksheet: Peak area of X: 4.99x10^4 a.u. Peak area of Y: 2.73x10^4 a.u. Density of X: 0.626 g/ml Density of Y: 0.703 g/ml Molar mass of compound X: 72.2 g/mol Molar mass of compound Y: 114. g/mol Relative response factor fr compound X: 1.00 Relative response factor fr compound Y: 1.21 Total volume of Fraction #2 - 8.0microliter Injection volume - 1.0milliliter Calculate the mole fraction of X.

0.76 irrelevant

#5 - Look at E5 Worksheet: Below is a phase diagram for a liquid mixture of A and B at 1.2 atm. What is the mole fraction of B in the vapors above a boiling solution containing 60%?

0.80

#21 - Look at E4 Worksheet: The student should combine fractions ________ containing purified cocaine and fractions ________ containing purified carfentanil. Fractions ________ will need to be purified again.

1 & 2; 5 & 6; 3 & 4

Look at #4 on E5 Practice Quiz: 1) What is the significance of the horizontal line between points X and Y? 2) Using the phase diagram, determine the molar composition of the vapor in equilibrium with a boiling liquid that has a composition of 80.% A and 20.% B. 3) Using the phase diagram, determine the molar composition of the vapor in equilibrium with a boiling liquid that has a composition of 40.% A and 60.% B.

1) A boiling liquid with composition X will produce vapor with composition Y - A boiling liquid with composition X will produce vapor with composition Y. 2) Percentage vapor composition A = 98% Percentage vapor composition B = 2% What is the boiling point of this liquid? 95C - The molar composition of the vapor in equilibrium with a boiling liquid that has a composition of 80.% A and 20.% B can be determined by drawing a vertical line from the x axis to the liquid curve at the point where the molar composition of A is 80. % (such as line WX on the diagram). A horizontal line is then drawn from the liquid curve to the vapor curve in the direction of the lower boiling point liquid (such as line XY on the diagram). This point corresponds to the molar composition of the vapor and by drawing a vertical line down to the x axis the values for A and B can be read. 3) Percentage vapor composition A = 80% Percentage vapor composition B = 20% What is the boiling point of this liquid? 120C

Correlate the microscale procedures needed to accomplish the given steps (1-5) to isolate pure isopentyl acetate (banana oil) from the reaction mixture.

1) Aqueous sodium bicarbonate is added to the reaction mixture. This deprotonates unreacted acetic acid, making a water soluble salt. 2) The mixture is stirred, capped and gently shaken, with frequent venting. This ensures that the evolution of carbon dioxide gas is complete. 3) The lower aqueous layer is removed using a Pasteur pipette and discarded. This removes byproducts. 4) The organic layer is dried over granular anhydrous sodium sulfate. This removes water from the product. 5) The dry ester is transferred using a Pasteur pipette to a clean conical vial. This separates the sodium sulfate from the ester.

1) If you separated a mixture of benzene, toluene, and m-xylene by gas chromatography, what would be the expected order of retention times? 2) Explain the order of elution Gas chromatography separates compounds depending on their _________ and volatility . Benzene, m-xylene, and toluene have similar _________, therefore, the main basis for separation is _________. The more volatile a component the _________, hence the more time it spends in the _________, giving it a ________ retention time. Therefore, components of a liquid mixture will elute in order of _________ boiling point.

1) Benzene (shortest retention time) -> toluene -> m-Xylene (longest retention time) 2) polarity and volatility; polarities; volatility Greater its vapor pressure; gaseous mobile phase; shorter Increased boiling point - Gas chromatography separates compounds depending on their polarity and volatility. Benzene, m-xylene, and toluene have similar polarities, therefore, the main basis for separation is volatility. The more volatile a component the greater its vapor pressure, hence the more time it spends in the gaseous mobile phase, giving it a shorter retention time. Therefore, components of a liquid mixture will elute in order of increasing boiling point

Predict the trend in boiling points for the following compounds (1 being the lowest boiling point).

1) Iso-Pentane 2) Pentane 3) Ethanol 4) Water 5) Sodium n-butoxide - The trend in strength of intermolecular interactions is: Ionic > Hydrogen bonding > Dipole-dipole > London dispersion For organic molecules which exhibit only London dispersion forces, the boiling point will increase with molecular weight and decrease with increasing branching. The greater the molecular weight, the greater the number of electrons there are to produce a temporary dipole, and the greater the distance over which the dipole can be formed. For a given molecular formula, increasing branching will decrease the boiling point, because the surface area available for London dispersion forces decreases.

Look at #9 on E5 Practice Quiz: Using the figure above, determine the boiling point of a liquid having a molar composition of 50% A and 50% B.

110C - According to the phase diagram above, a mixture of A and B of composition w will have the following behavior when heated. The temperature of the liquid mixture will increase until the boiling point of the mixture is reached. This corresponds to following line wx from w to x, the boiling point of the mixture t. Following the same steps described above, a liquid having a molar composition of 50% A and 50% B would boil at about 110 °C

A student was carrying out a Fischer Esterification reaction using toluene (b.p. 111C) as the solvent. He wrote in his lab notebook that the heating mantle surface temperature was 250C and that the reaction was boiling vigorously. What was the temperature of the reaction mixture?

111C

During the microscale boiling-point determination of an unknown liquid, heating was discontinued at 154 °C and the liquid immediately began to enter the inverted bell. Heating was begun again at once, and the liquid was forced out of the bell. Heating was again discontinued at 165 °C, at which time a very rapid stream of bubbles emerged from the bell. On cooling, the rate of bubbling gradually diminished until the liquid reached a temperature of 161 °C and entered and filled the bell. What was the boiling point of the liquid?

161 °C - The true boiling point of the liquid was 161 °C. If you stop heating at any point below the true boiling point when using this method, the liquid will be forced into the capillary tube. This is what happened at 154 °C. Heating to 165 °C carried the temperature above the boiling point as should be done for this method.

The IR spectrum shown is for the aldehyde, propanal, and the molecule is showing the stretching of the C=O bond. Which wavenumber range is the band for the C=O stretch?

1760-1665 - The characteristic carbonyl C=O stretch is in the range 1760-1665 cm -1 .

A student attempted to separate hexane and heptane by distillation. He used GC analysis to analyze the contents of each fraction and determine the separation efficacy. Unknown: RT - 1) 1.062 2) 2.272 Area - 1) 4240 2) 63289 Type - 1) PB 2) PB Width - 1) 0.078 2) 0.221 Area % - 1) 6.24632 2) 93.23662 1:1 hexane/heptane standard: RT - 1) 1.120 2) 2.279 Area - 1) 31447 2) 36917 Type - 1) PV 2) BB Width - 1) 0.086 2) 0.191 Area % - 1) 45.99936 2) 54.00064 The retention time of the second peak to elute in the student sample is ______ min. The integral of the second peak to elute in the student's sample is ______ a.u. The second peak in the students' sample corresponds to ______.

2.272; 63300; heptane

Look at #12 E6 Worksheet: A student needs to determine the % yield for her E6 Fischer Esterification reaction using the following data tables. Calculate the Reaction % Yield

Look at #17 on E5 Worksheet: Determine the volume response factor for a 1:1 mixture (by volume) of compound A and compound B. If the response factor of compound A is arbitrarily assigned to 1.00, determine the relative response factor for compound B. Peak area of compound A: 26,370 a.u. Peak area of compound B: 21,574 a.u.

26,379/26,379 = 1 21,574/26,379 = 0.82

Look at #21 E5 Practice Quiz:

3.9 g = 0.05 moles benzene; 4.6 g = 0.05 moles toluene Partial vapor pressure of benzene = (270 mmHg)(0.5) = 135 mmHg At 90 °C, Ptotal = (1010 mmHg)(0.5) + (405 mmHg)(0.5) = 707 mmHg At 100 °C , Ptotal = (1340 mmHg)(0.5) + (560 mmHg)(0.5) = 950 mmHg Therefore, boiling point at atmospheric pressure (752 mmHg) is greater than 90 °C, but less than 100 °C. Assuming a linear relationship between the vapor pressure of each substance in the temperature range of 90 °C to 100 °C, the change in vapour pressure for each 2 °C change in temperature can be calculated. The following approximate vapor pressures are obtained at certain temperatures: Temperature (°C)Partial pressure of benzene (mmHg)Partial pressure of toluene (mmHg)90505202.592 538 218 94571233.59660424998637264.5100670280 At 92 °C Ptotal = (1076 mmHg)(0.5) + (436 mmHg)(0.5) = 538 mmHg + 218 mmHg = 756 mmHg This value is the closest to atmospheric pressure (752 mmHg), thus the boiling point is approximately 92 °C Partial vapor pressure of benzene at 92 °C = (1076 mmHg)(0.5) = 538 mmHg Partial vapor pressure of toluene at 92 °C = (436 mmHg)(0.5) = 218 mmHg 0.71 moles = 55.4 g benzene; 0.29 moles = 26.7 g toluene Therefore, the percentage composition by weight of toluene is 32.5%.

The IR spectrum shown is for acetone, and the molecule is showing the stretching of the C-H bonds.Which wavenumber range is the band for the C-H stretch?

3100-3000 - C-H stretches are in the range 3100-3000 cm -1 .

Look at #15 E6 Worksheet: Shown below is the FT-IR spectrum of an unknown compound from E6. Rank the labelled peaks by their interpretive power in qualitative functional group identification.

3310 cm-1: Great 2872 cm-1: Medium/weak 1453 cm-1: Do not use 1009 cm-1: Do not use The unknown compound is most likely an alcohol

The IR spectrum shown is for propanol, and the molecule is showing the stretching of the O-H bond. Which wavenumber range is the band for the O-H stretch?

3500-3200 - O-H stretches are in the range 3500-3200 cm -1 .

Look at #10 E6 Worksheet: During E6, a student successfully identified benzyl acetate as her product ester. Enter the molar equivalents of acetic acid

4.5

#4 - Look at E5 Worksheet: Below is the phase diagram for a mixture of toluene and octane at 1.1 atm pressure. What is the BP of a liquid that has a composition of 70% toluene in degrees Celcius?

Look at #2 on E5 Practice Quiz: From the plot of vapor pressures vs temperature above, estimate the boiling point of heptane when the external pressure is 595 mm Hg.

90C - The boiling point is the temperature at which the vapor pressure is equal to the external pressure. From the graph, the vapor pressure of heptane is estimated to be 595 mm Hg at 90 °C.

Which is the best description of a fractional distillation?

A technique to separate liquid mixtures with boiling points close to each other. - In distillation, the usual objective is to separate one component from a mixture. A mixture of liquids with boiling points that differ by less than 30°C can be separated using fractional distillation.

Look at #3 on E5 Practice Quiz: SAFETY: If using plastic joint clips to stabilize your equipment, which clips in the diagram should NOT be used?

A, B - These clips are not heat proof and so can melt if they are too close to the heated part of the apparatus.

#10 - Look at E5 Worksheet: Which glass joint in the following distillation apparatus should NOT be secured by a plastic keck clip?

A, on the bottom

#11 - Look at E5 Worksheet: Identify the indicated glassware and equipment for the following experimental setup

A. Distillation head B. Thermometer adapter C. Thermometer D. Water out E. Water in F. Condenser G. Vacuum (bent) adapter This entire set-up is called: simple distillation

Look at #9 on E5 Practice Quiz: SAFETY: If using plastic joint clips to stabilize your equipment, which of the clips in the diagram should NOT be used?

A; closest too heat source

Which of the following solvents would be the best to separate a mixture containing benzoic acid, 2,4-dinitrobenzoic acid, and 2,4,6-trinitrobenzoic acid by TLC?

Acetone - Acetone should work well because the mixture is highly polar. An acetone-hexane mixture might work well, too.

Look at #2 on E6 Concept Quiz: Dimethylaminopyridine (DMAP) is often used as a catalyst in esterification reactions. A basic solvent such as triethylamine is used to react with the liberated proton from the alcohol group. Draw curved arrows to show the movement of electrons in this step of the mechanism.

Alcohol attacks carbonyl carbon, double bond transfers electrons to carbonyl O - The alcohol makes a nucleophilic attack on the carbonyl group, forming a tetrahedral intermediate.

Look at #6 E7 Worksheet: Which possible functional group best matches the above IR Spectrum?

Alcohol or ketone/aldehyde

A student is attempting to purify ferrocene, 9-fluorenone, and acetyl-ferrocene on a silica column using step-wise addition of petroleum ether, a petroleum ether/MTBE mixture, and then MTBE. What will most likely elute in fraction 1 (using TLC) if her partner swapped the labels on her petroleum ether bottle and the bottle containing the petroleum ether/MTBE mixture.

All of the least polar compound will elute along with some of the medium polar compound

#13 - Look at E4 Worksheet: Elinor Rabbit spotted her unknown analgesic and standards on a TLC plate. After allowing the TLC to develop in the chamber, she visualized the plate under the UV lamp. Using Table 1 in the Lab handout and the following TLC plate, select the best option below to help Elinor complete her scientific claim for Part B.

Anacin

Look at #18 E7 Practice Quiz: Which of the peaks in the infrared spectrum for ethyl acetate is for the carbonyl (C=O) functional group?

B - Carbonyl peaks are strong, sharp absorptions between 1760 - 1665 cm -1 .

Look at #16 E6 Worksheet: Shown below is the FT-IR spectrum of a potential ester product from E6. Match the unknown ester IR spectrum to an IR spectral database of known esters from Table 1 in the lab handout. The most likely identity for the unknown ester:

Benzyl acetate

Look at #18 E6 Worksheet: A student obtained the following GC data upon co-injecting her unknown ester from E6 with the 1:1:1:1 standard. What is the identity of the unknown ester?

Benzyl acetate

Consider a sample that is a mixture composed of biphenyl, benzoic acid, and benzyl alcohol. Predict the order of elution of the components in this mixture. Assume that the chromatography uses a silica column and the solvent system is based on cyclohexane, with an increasing proportion of methylene chloride added as a function of time.

Biphenyl (elutes first) > benzyl alcohol > benzoic acid (elutes last) - When using a nonpolar solvent, such as cyclohexane, you should expect the relatively nonpolar substance to elute first (biphenyl)

What can you do to elute a compound that is not coming off the column?

Change to a more polar solvent - A standard silica or alumina column with a polar stationary phase polar compound will elute slowly with non-polar solvents. A more polar solvent will compete with the compound to adsorb to the stationary phase, so it will start to elute.

Look at #18 E7 Worksheet: Using Appendix A in the lab handout, the identity of the unknown is ______ The data that best supports this claim is the ______ The data that is least reliable is the ______

Citronellal Derivative melting point Boiling point

A student suspected he might've mixed up his chemicals and decided to run some tests he learned in CHEM43A. He obtained the following data: Boiling point: 151C 2,4-DNP test: positive Tollens Test: negative First, consider potential matches in Appendix A and then indicate which chemical derivative he should prepare to best confirm the identity of the unknown compound?

DNP

Which of the following statements best describes the experimental objective of Part A in Experiment 4?

Determine the relative polarity of acetophenone isomers with TLC

What type(s) of intermolecular forces are expected between CH3CH2CH2CH2CH2CH2OH molecules?

Dipole forces, induced dipole forces, hydrogen bonding

What type(s) of intermolecular forces are expected between CH3CH2CH2CH2OH molecules?

Dipole forces, induced dipole forces, hydrogen bonding

SAFETY: While setting up a micro-boiling point determination you accidentally break a capillary tube. You should:

Dispose of it in the appropriate glass waste container. - Broken glass is sharp and could cause harm to you or others. Capillary tubes are small and could easily be lost so you should put them in the appropriate glass waste container immediately. If you are unsure of where to dispose of broken glass ask your instructor

SAFETY: While setting up a micro-boiling point determination you accidently break a capillary tube. You should:

Why are the techniques or results of Experiment 5 important?

Distillation and GC separate and determine the purity and identification of liquids with diff VPs. Distillation: alcohol GC: labs

What is the purpose of synthesizing a chemical derivative in E7?

Easier to purify to find unknown compound + accurate MP + IR + product yield + confirm identity

Look at #2 on E6 Concept Quiz retake: Dimethylaminopyridine (DMAP) is often used as a catalyst in esterification reactions. A basic solvent such as triethylamine is used to react with the liberated proton from the alcohol group. Draw curved arrows to show the movement of electrons in this step of the mechanism.

Electrons pushed to form double bond, bond breaks to separate DMAP (bond to benzyl), next double bond goes to next carbon, double bond restores electron for N+ - Collapse of the tetrahedral intermediate results in expulsion of the DMAP catalyst and yields the target ester.

Look at #5 E6 Worksheet: You successfully identified hexyl acetate in E6. Draw the net chemical reaction (not a mechanism) used to make your ester

Equilibrium arrows (H2SO4 + reflux) water in product

Look at #5 E6 Worksheet: Consider esters 1-3 that can be prepared from an alcohol and carboxylic acid under Fischer Esterification reaction conditions. Determine which alcohol (A-E) and which carboxylic acid (F=J) are needed to prepare each ester

Ester #1: Alcohol E, acid G Ester #2: Alcohol B, acid H Ester #3: Alcohol D, acid I

State why the techniques or results of Experiment 6

Fischer esterification: perfumes

What characteristic odor would you expect to observe if an alcohol reacted with acidified ethanoic acid?

Fruity smell

Look at #21 on E5 Worksheet:

GRAPHS!

Which of the following is a GHS hazard code for benzyl alcohol?

H302 - Harmful if swallowed

Which of the following is not a GHS hazard code for 1-propanol?

H350 - May cause cancer

Which of the following is true about the inverted capillary method for boiling point determination using a Thiele tube? More than one answer may be correct.

Heat should only be applied to the side arm of the Thiele tube. After the sample is boiling and the heat has been turned off, the boiling point should be recorded at the point when the liquid sample enters the capillary tube. It requires the smallest volume of sample. - It is best to heat the sample gently so that the two streams of bubbles are easily distinguishable. The first, slow stream of bubbles corresponds to air within the capillary tube expanding and the second, rapid stream of bubbles corresponds to the liquid boiling. The Thiele tube should be heated by passing the flame of a Bunsen burner along the side arm which creates a uniform distribution of heat in the oil by convection currents. The micro-boiling point determination only requires a small amount of sample (typically no more than 0.5 mL).

Which of the following solvents would be the best to separate a mixture containing bromobenzene and p-xylene by TLC?

Hexane should work well because both compounds are relatively non-polar.

What features make a sample suitable for analysis by gas chromatography? (More than one answer may be correct.)

High vapor pressure. Thermal stability. Appreciable volatility. - Gas chromatography involves a gaseous mobile phase and stationary phase, therefore, the sample must be volatile enough that it can be vaporized and carried into the column by the carrier gas. Samples that are too involatile to be analyzed by GC can be derivatized. The compounds in the samples must be thermally stable at the temperature required for analysis by GC. Certain functional groups are less thermally stable than others, therefore, samples can be derivatized to increase thermal stability.

Look at #17 E7 Practice Quiz: The infrared region between 3650 cm -1 and 2650 cm -1 is shown for a molecule. What functional group does the molecule contain?

Hydroxyl (-OH) - A broad peak between 3650 - 3050 wavenumbers is indicative of an -OH group. The peak is quite U-shaped, which would suggest an alcohol rather than a carboxylic acid (which have more V-shaped peaks).Lack of a C=O peak around 1700 cm -1 would provide further confirmation of this.

Briefly state the objective of Experiment 7

Identify unknown's identity by identifying its FG and preparing a chemical derivative and determine MP

What rate should the liquid come across in a fractional distillation?

In fractional distillation, it is extremely important to distill slowly, as it is more likely that you will get mixed fractions distilling over unless you take care.

SAFETY: How should the silica be disposed of at the end of the experiment?

In the appropriate waste solid container. - The silica is a solid and should be disposed of in the appropriate manner. Check with your instructor where to dispose of the silica before starting the procedure.

Why is it useful to be able to determine the boiling point of a compound? More than one answer may be correct.

It can be used to determine the purity of a product. It can be used to help identify unknown compounds. It can be used to help purify products - Chemists can compare measured boiling points of unknown compounds to a table of literature values to help identify a compound. The deviation of the boiling point of a liquid product from the literature value can indicate the presence of impurities. Liquid products can be distilled at the literature boiling point to separate them from higher boiling point liquid impurities.

SAFETY: Which of these are safety concerns related to the use of UV light to expose spots on a TLC plate?

It can damage your eyes if looked at directly. - If using UV light to visualize the spots on a TLC plate, do not look directly into the light. UV light can damage your eyes.

Which of the following is true about the inverted capillary method for boiling point determination using a Thiele tube? More than one answer may be correct.

It requires the smallest volume of sample. After the sample is boiling and the heat has been turned off, the boiling point should be recorded at the point when the liquid sample enters the capillary tube. Heat should only be applied to the side arm of the Thiele tube. - It is best to heat the sample gently so that the two streams of bubbles are easily distinguishable. The first, slow stream of bubbles corresponds to air within the capillary tube expanding and the second, rapid stream of bubbles corresponds to the liquid boiling. The Thiele tube should be heated by passing the flame of a Bunsen burner along the side arm which creates a uniform distribution of heat in the oil by convection currents. The micro-boiling point determination only requires a small amount of sample (typically no more than 0.5 mL).

Match the chemical test with the corresponding positive result.

Jones Test: blue-green color Lucas Test: cloudiness Tollens Test: silver mirror 2,4-DNP Test: red-orange precipitate

Which test would distinguish a 1° alcohol and 3° alcohol?

Jones test

Look at #13 E7 Worksheet: A student found a vial of liquid while cleaning out the Pokemon Center storage. Remembering what she once learned in carrying out E7 in CHEM43A, she decided to run some tests to narrow down the identity of the mysterious liquid.

Jones: negative 2,4-DNP: positive Scientific claim: She concludes that the compound contains a ketone

Jones: positive Lucas: positive Scientific claim: She concludes that the compound contains a secondary alcohol

SAFETY: How much should you fill your distillation pot?

Less than half full - Do not overfill your reaction flask. It should be less than half full. If you have too much sample, you should use a larger flask.

Based on the IR spectrum, a student determined her unknown contained a carbonyl functional group and decided to perform the Lucas test as her negative test. But she was surprised and confused when she observed two layers form.

Limited to 1 alc vs 2 and 3 alc +: cloudiness (false positive here) because water + unknown aren't miscible

When performing a fractional distillation, how can you tell when your liquid is beginning to distill over? More than one answer may be correct.

Liquid droplets start to condense on the thermometer bulb. The temperature remains constant after initially rising. - The temperature will begin to rise when you start heating your sample, but the liquid will only start to distill when it is boiling and vapor is rising up to the still head and thermometer bulb. A tell-tale sign is to see droplets forming on the thermometer bulb.

In Gas chromatography the stationary phase is ______ and the mobile phase is ______. Compounds will separate on a GC column depending on their ______. When compounds have similar polarities, the less volatile compounds will spend ______ time in the gas phase and will have ______ retention times. Generally, compound with the ______ boiling point will elute first.

Liquid; gas; volatility and polarity; less; longer; lowest

Kiryu and Majima are CHEM 43A lab neighbors and share the same chemical fume hood. Both are busy preparing their chemical derivatives for E7. Majima finishes and heads over to the instrument room to acquire the IR spectra of his derivative. He tries to be helpful and moves some of the recently used glassware out onto the bench to clear up space in the hood. However, everyone in lab soon notices a foul stench emanating from Kiryu and Majima's area. The TA quickly walks over and remarks that something smells strongly of pyridine. Identify the hazard and explain how Kiryu and Majima should fix the issue and explain how Majima could have prevented the issue (and minimize exposure) by following general prudent lab practices.

Majima should not have left his items unattended + should have cleaned + should have disposed pyridine into to liquid waste container + done RAMP assessment Flammable Irritation of skin, eyes, respiration Leave room Could've prevented by leaving it in the fume hood instead rather than bench since now everyone can smell it

Look at #12 E7 Worksheet: Which of the following compound(s) would you expect to give a positive result for both the Jones test and the 2,4-DNP test?

O, X, X, X

Look at #17 E6 Worksheet: Use E6 1:1:1:1 GC standard chromatogram in Figure 1 to answer next 2 questions

Order: Isopentyl acetate n-Hexyl acetate n-Heptyl acetate Benzyl acetate

State why the techniques or results in Part C of Experiment 4 are important.

Pharmaceutical benefits

Look at #17 E7 Worksheet: Beaker collected the following data when analyzing his unknown liquid during E7 Unknown BP: 198C Tollens Test: Inconclusive Jones Test: Positive DNP Derivative melting point: 121.4-122.7C *peak at carbonyl

Phenylacetaldehyde

The stationary phase in TLC is ________. Therefore, the _________ component of the mixture will travel a greater distance up the plate, resulting in a ________ value for the component. When separating a mixture containing bromobenzene and p-xylene, the ________ spot would be expected to travel the greatest distance up the plate as it is the _________ component. The ________ would travel the least distance as it is the _________ component.

Polar; less polar; higher Rf Benzoic acid; least polar; 2,4,6-trinitrobenzoic acidbenzoic acid; most polar - When separating a mixture containing benzoic acid, 2,4-dinitrobenzoic acid, and 2,4,6-trinitrobenzoic acid, the benzoic acid spot would be expected to travel the greatest distance up the plate as it is the least polar component, hence interacts with the stationary phase less. The 2,4,6-trinitrobenzoic acid would travel the least distance as it is the most polar component, hence interacts with the stationary phase more.

Polar; less polar; higher Rf P-xylene; least polar; bromobenzene; most polar - The stationary phase in TLC is polar. Therefore, the less polar component of the mixture will travel a greater distance up the plate, resulting in a higher Rf value for the component. When separating a mixture containing bromobenzene and p-xylene, the p-xylene spot would be expected to travel the greatest distance up the plate as it is the less polar component, hence interacts with the stationary phase less. The bromobenzene would travel the least distance as it is the more polar component, hence interacts with the stationary phase more.

A student suspected he might've mixed up his chemicals and decided to run some tests he learned in CHEM43A. He obtained the following data: Boiling point: 127C 2,4-DNP test: positive Tollens Test: negative First, consider potential matches in Appendix A and then indicate which chemical derivative he should prepare to best confirm the identity of the unknown compound?

Semicarbazone

Look at #19 on E5 Worksheet: Interpret the GC results - determine the contents of each fraction and decide if the separation was successful

Simple Distillation Fraction #1: Mostly pure (>= 4:1 ratio) hexane Fraction #2: A mixture of hexane/heptane Fraction #3: A mixture of hexane/heptane Fraction #4: A mixture of hexane/heptane Fraction #5: A mixture of hexane/heptane Fractional Distillation Fraction #1: Pure (>=9:1 ratio) hexane Fraction #2: Mostly pure (>= 4:1 ratio) hexane Fraction #3: A mixture of hexane/heptane Fraction #4: A mixture of hexane/heptane Fraction #5: Pure (>=9:1 ratio) heptane Scientific argumentation - Scientific Claim Fractional distillation provided the most effective separation

You are required to separate a mixture of two solvents. One has a boiling point of 45°C, and the other has a boiling point of 120°C. Which of the following is the most appropriate type of distillation to use?

Simple distillation - There is no need to use anything other than simple distillation to separate these components.

Which of the following statements best describes what you would observe on the final TLC if the solvent level was above the baseline and spots when running the TLC plate?

Spots will be absent from TLC plate

State why the techniques or results of E7 are important

Support info for known BP, MP of chemical derivatives, and IR in unknown compounds. Pharmaceutical benefits

Which of the following statements best describes the motivation for Parts A and B?

TLC can be used to identify compounds and determine purity. It's regularly used in chemistry labs to check reactions, identify compounds and determine optimal conditions for purification by column chromatography

The functional groups in an organic compound can frequently be deduced from its infrared absorption spectrum. A compound, C3H6O2, exhibits intense absorption at 1740 cm-1, accompanied by a band at 1050 cm-1. No absorption above 3000 cm-1 is present .Relative absorption intensity: (s)=strong, (m)=medium, (w)=weak.What functional class(es) does the compound belong to?List only classes for which evidence is given here. Attach no significance to evidence not cited explicitly.Do not over-interpret exact absorption band positions. None of your inferences should depend on small differences like 10 to 20 cm-1.

The C=O stretch at 1740 cm-1 confirms a carbonyl and 1050 cm-1 is C-O stretch. Since there is no O-H stretch above 3000 cm-1, this must be an ester.

The functional groups in an organic compound can frequently be deduced from its infrared absorption spectrum. A C6 hydrocarbon exhibits bands between 3000-3100 (w), 2850-2960 (m), and at 1650 cm-1 (w).Relative absorption intensity: (s)=strong, (m)=medium, (w)=weak.What functional class(es) does the compound belong to?List only classes for which evidence is given here. Attach no significance to evidence not cited explicitly.Do not over-interpret exact absorption band positions. None of your inferences should depend on small differences like 10 to 20 cm-1.

The absorption above 3000 is sp2 =C-H stretch, and 1650 cm-1 is C=C stretch.

In a vacuum distillation, what is the effect of using reduced pressure?

The boiling point of the fractions are decreased - Reducing the pressure reduces the boiling point.

The functional groups in an organic compound can frequently be deduced from its infrared absorption spectrum. A compound, C5H10O2, exhibits strong, broad absorption across the 2500-3200 cm-1 region and an intense absorption at 1715 cm-1.Relative absorption intensity: (s)=strong, (m)=medium, (w)=weak.What functional class(es) does the compound belong to?List only classes for which evidence is given here. Attach no significance to evidence not cited explicitly.Do not over-interpret exact absorption band positions. None of your inferences should depend on small differences like 10 to 20 cm-1.

The broad, strong 2500-3200 absorption is the signature O-H stretch of a carboxylic acid. The presence of C=O stretch at 1715 cm-1 confirms this conclusion.

Why should the solvent level in the elution tank be below the level of the baseline of the TLC plate?

The compound in the spots would dissolve into the solvent if it were higher. - If the spots dissolve into the solvent, they will not move up the plate and be resolved.

Select the statement that best explains which compound in the previous question above will elute last

The compound that elutes last is relatively polar and strongly interacts with the stationary phase through dipole-dipole and hydrogen bonding interactions

A student obtained boiling point data from 3 separate measurements (using a fresh sample each time) and isolating his unknown ester product from the Esterification reaction in E6. Observed BP #1: 94C Observed BP #2: 105C Observed BP #3: 82C Unfortunately, the observed boiling points don't match any of the potential ester products in Table 1 in the Lab Manual Handout. Which of the statements is the most plausible explanation?

The ester product contains a significant fraction of MTBE

Why shouldn't the start line, where the solution mixtures are initially placed, be drawn in ink?

The ink is likely to dissolve in the solvent and will add extra spots to the chromatogram. - Pen inks tend to be soluble in organic solvents of most polarities and would contaminate the chromatogram.

Which of the following statements concerning the principle of separation in gas chromatography is true when using a liquid stationary phase? (More than one answer may be correct.)

The lower the vapor pressure of a compound, the lower the amount that will be in the mobile phase at equilibrium, hence the slower the compound will travel through the column. The higher the vapor pressure of a compound, the greater the amount that will be in the mobile phase at equilibrium, hence the faster the compound will travel through the column. - Compounds are separated in the column based on the level of interaction with the stationary phase. The greater the interaction with the stationary phase the slower the compound will travel through the column. When the gaseous sample enters the column, it condenses and dissolves in the liquid stationary phase until its equilibrium vapor pressure has been reached. The lower the vapor pressure of a compound, the greater its interaction with the stationary phase. Therefore, factors that affect vapor pressure, such as size, affect the level of interaction with the stationary phase.

The functional groups in an organic compound can frequently be deduced from its infrared absorption spectrum. The only absorption bands this compound exhibits are 2850-3000 (m) and 1450 cm-1 (w).Relative absorption intensity: (s)=strong, (m)=medium, (w)=weak.What functional class(es) does the compound belong to?List only classes for which evidence is given here. Attach no significance to evidence not cited explicitly.Do not over-interpret exact absorption band positions. None of your inferences should depend on small differences like 10 to 20 cm-1.

The only bands are C-H stretch and C-H bend.

What observation would you expect to make if a primary or secondary alcohol reacted with acidified potassium dichromate(VI) solution?

The orange solution turns green. - The orange dichromate(VI) ions are reduced to green chromium(III) ions.

#12 - Look at E4 Worksheet: An ortho and para hydroxy acetophenone isomers have different Rf values under the same conditions; the ortho isomer had a much higher Rf value. Think about why the two hydroxy acetophenone isomers have such different Rf values. Then consider the following two methoxy acetophenone isomers (ortho vs. para) and select the statement that a) correctly predicts the relative Rf values of the following two compounds and b) provides the correct reasoning

The para isomer has a larger dipole = smaller Rf

IR spectroscopy can be used to determine which of the following? More than one answer may be correct.

The presence of impurities in a product The absence of certain groups from a molecule. The presence of certain bonds within a molecule - We cannot determine the molecular mass of a sample by IR spectroscopy, but we can determine absence and presence of certain groups or of impurities in a sample.

What is the consequence of the gas flow rate being too high?

The sample won't have a chance to equilibrate with the stationary phase, leading to poor separation. - The flow rate must be slow enough for the compounds to equilibrate with the stationary phase so that they can be separated based on their equilibrium vapor pressures. However, if the flow rate is too slow, the peaks become broad (poor resolution) due to the diffusion of the compounds in the gas phase.

What is the effect of using a longer column?

The separation will be more effective, as the sample undergoes more partitioning between the mobile and stationary phases. - In a longer column, the compounds undergo greater partitioning between the mobile and stationary phases, hence the difference in the interaction of the compounds with the stationary phase is accentuated and separation is more effective.

What happens if the spots are made too large when preparing a TLC plate for development?

The spots will saturate the plate, show tailing, and/or diffuse into one another - If the spots are made too large they may saturate the slide, show tailing, diffuse radially outward, or run into one another.

The DHr (enthalpy of reaction) for Fischer Esterification reaction is usually ~0, indicating that neither products nor reactants are strongly favored (Keq ~1). Thus the reaction is reversible and under equilibrium. According to the manual, the reaction is finished after heating for 1hr at reflux. What would be the likely effect on the reaction yield if the reaction was carried out at a temperature 10 degrees lower while keeping the reaction time constant and why?

The yield will be lower since the reaction will go slower

SAFETY: TLC spotters are sharp. The MAJOR safety concern when using spotters is that:

They can cause stab injuries - Spotters are sharp and can cause stab injuries.

Why is it necessary to recrystallize the derivative?

To ensure purity

Why might you want to heat a reaction? More than one answer may be correct.

To increase the rate of the reaction. To overcome the activation energy for the reaction. - In order for some reactions to proceed they require extra energy, which can be supplied in the form of heat, to overcome the activation energy for the reaction. Applying heat also increases the rate of the reaction since the reactive species will have greater kinetic energy, resulting in more successful collisions with the required energy to react.

Which of the following is an appropriate use for distillation apparatus? More than one answer may be correct.

To measure a boiling point of a liquid To remove a liquid product from a reaction mixture - If the objective is to collect a solid from a liquid, use filtration, not distillation. Distillation can be used to remove a liquid from a reaction mixture, and can be used to measure the boiling point of a liquid. Fractional distillation is often used to separate a mixture of solvents.

When setting up a column, what is the reason for adding a layer of sand on top of the adsorbent column?

To prevent disruption of the surface when solvent is added - It is important that the surface of the silica is level and not disturbed. If the surface is disturbed, the compounds will not travel through the column as cylindrical bands; instead, these bands will be uneven. This may give a poorer separation, especially if the compounds elute from the column close together.

Why should the cold end of the apparatus be open to the atmosphere in a distillation set-up?

To prevent pressure build up, which could cause an explosion. - The collection end is either fitted with an adaptor to connect to a round bottom flask clipped to it or the liquid drips into a collection vessel below the adaptor. The adaptor should have a side arm on it to prevent pressure build up.

What is the reason for the layer of sand at the bottom of the column?

To prevent the adsorbent from passing through to the tap - The sand provides a base on which the adsorbent column can sit and prevents it from running through to the tap.

Tollens: positive Lucas: negative Scientific claim: She concludes that the compound contains an aldehyde

Which of the two of the following compounds would be at least difficult to separate by distillation? Boiling points; Cyclohexane: 81C Toluene 111C Diethyl ether 35C

Toluene and diethyl ether

A mountaineer is boiling water to cook pasta at the top of a mountain. The boiling point of water is lower on the mountain than at sea level.

True - The mountaineer is at higher altitude on the mountain than at sea level. As altitude increases, the air pressure decreases. Therefore, the vapor pressure of the water needs to be raised to a lesser pressure to make the liquid boil, thus the boiling point is lower.

SAFETY: When performing a distillation, the collection end should be in some way open to the atmosphere.

True - There should always be an outlet to prevent pressure build-up. Do not create a closed system, which could explode when heated.

How long should you run a TLC plate for?

Until the solvent front is just below the top of the plate.

How long should you run a TLC plate for?

Until the solvent front is just below the top of the plate. - You should maximize the length of the run in order to get good separation; however, be aware that the longer the plate is run, the more diffuse the spots will become.

Briefly state the objective of Experiment 6

Use Fischer Esterification to transform the starting unknown alcohol and determine the presence/absence of FG (and identity of starting alcohol) through IR, BP, and GC

Two liquids have boiling points which are less than 20 °C apart. How can a simple distillation be modified to improve the separation?

Use a fractioning column - Two closely boiling liquids can be separated by adding a fractionating column between the flask and the still head.

#9 - Look at E5 Worksheet: Which is the first, and most important, position in the following distillation apparatus that should be secured by a clamp

VII, on the bottom

Look at #11 E6 Worksheet: During E6, a student successfully identified n-Hexyl acetate acetate as her product ester. Enter the molar equivalents of sulfuric acid.

WRONG

Which of the following statements concerning the principle of separation in gas chromatography is true when using a liquid stationary phase? More than one answer may be correct.

When the sample enters the column, the compounds dissolve to varying extents in the stationary phase. The extent to which a molecule interacts with the stationary phase depends on its size. - Compounds are separated in the column based on the level of interaction with the stationary phase. The greater the interaction with the stationary phase the slower the compound will travel through the column. When the gaseous sample enters the column, it condenses and dissolves in the liquid stationary phase until its equilibrium vapor pressure has been reached. The lower the vapor pressure of a compound, the greater its interaction with the stationary phase. Therefore, factors that affect vapor pressure, such as size, affect the level of interaction with the stationary phase. The higher the vapor pressure of a compound, the greater the proportion that remains in the mobile gas phase, hence the faster the compound gets carried through the column by the carrier gas.

Which of the following factors affect boiling point? More than one answer may be correct.

Whether a compound is polar or not. The pressure. - The boiling point depends on the pressure, molecular weight, structure, and purity of the liquid. The vapor pressure of the liquid must equal the external pressure in order for boiling to occur, therefore, the boiling point decreases with decreasing pressure and less energy is required to make the liquid boil. The structure of a compound determines the strength of intermolecular interactions that hold the molecules in the liquid phase: polar compounds have dipole-dipole and, potentially, hydrogen bonding, whereas, nonpolar compounds have van der Waals interactions.

Which of the following factors affect boiling point? More than one answer may be correct.

Look at #12 E7 Worksheet: Which of the following compound(s) would you expect to give a positive result for the Jones test but negative for the 2,4-DNP test?

X, O, O, X

When setting up a fractional distillation, the main difference from a simple distillation is:

You need to add a column between the flask and the distillation head. - The addition of a fractionating column allows a more controlled separation of components.

A student was running a column to separate her desired compound, a potential small-molecule anti-cancer drug (Rf=0.32) from an impurity with deadly side effects (Rf=0.42). She decided to run a slow gradient starting with 100% hexane and slowly increasing to 15% Ethyl acetate mixture to ensure perfect separation. As she slowly increases the solvent polarity to ~10% Ethyl acetate:hexane she noticed a crack in the silica gel had formed in her column. She finishes her column and prepares to analyze her fractions by TLC using a 5% Ethyl Acetate mixture as the mobile phase. What will she see in her TLC analysis and briefly explain how cracks in the silica gel can affect column chromatography results.

a) cracks in a column causes poor separation due to uneven silica density/flow (channeling) rate AND b) correctly explains TLC analysis (b) will show impure fractions (multiple spots) or compound/s coming off column early

A student was carrying out his fractional distillation and had properly set up all his distillation apparatus. He slowly ramped up the temperature on his distillation until he achieved a steady drop rate of 1 drop/sec. After a few minutes of collecting his sample, he increased the heat on the hotplate until it was ~5 drop/sec. His partner ran his GC samples for him. But when the student later analyzed his GC data, it wasn't what he expected.

a) heating/drip rate was too fast which causes vapors to quickly pass through fractionating column with poor separation AND b) GC data will show impure fractions with multiple peaks.

A student was having some issues and decided to practice his simple distillation technique using a mixture of octane and hexane. He had his partner confirm that he was doing everything correctly. But no matter how many times he set up and ran the simple distillation, he couldn't understand why the thermometer always read above the BP of hexane when the first drops were being collected in the receiving flask.

a) vapors in a simple distillation are not pure (i.e. a mix of octane and hexane) (b) and thus the condensation temp (i.e. bp) of the mixture is higher - due to the presence of the less volatile octane

Look at #16 E7 Worksheet: A student was assigned an unknown liquid to identify in Experiment 7. He collected the following IR spectrum of the unknown: Based on the above IR, Jimmy determined the compound to contain an ______ He then synthesized ______ After recrystallization, Jimmy obtained the following spectrum of the unknown derivative and developed his argument. Scientific Claim: The formation of the derivative was ______. Supporting Data: The data that best supports his claim is ______ and ______.

alcohol; 3,5-dinitrobenzoate ester derivative Successful Disappearance of the peak at 3300 Appearance of the peak at 1720

aldehyde or ketone; 2,4-dinitrophenyl hydrazone derivative Successful Disappearance of the peak at 1712 Appearance of the peak at 1620

Observing the formation of a silver mirror on the surface of a test tube when using Tollen's reagent indicates the presence of:

an aldehyde. - The test for an aldehyde uses Tollen's reagent, which is essentially a solution of silver ions in ammonia solution. If an aldehyde is present, a precipitate of silver, which looks like a mirror, forms on the inside surface of the test tube.

SAFETY: When derivatizing an alcohol with trimethylsilyl chloride, you should:

carry out the reaction in a fume cupboard - Reacting trimethylsilyl chloride (TMSCl) with alcohols is a common example of derivatization. Trimethylsilyl chloride is highly flammable, reacts violently with water, and causes severe burns. Therefore, TMSCl should not be used in the presence of ignition sources, in the presence of water, or without the appropriate protective clothing. The reaction produces HCl, and should be carried out in a fume cupboard.

A gas chromatograph can be used to (more than one answer may be correct)

determine the purity of a product; separate vaporizable compounds - A gas chromatograph can be used to separate vaporizable compounds. They can determine the purity of products by accurately detecting the presence of any impurities. Furthermore, the percentage composition of a mixture can be determined. Products can be identified by their retention times if there is a known or literature value for comparison. A gas chromatograph needs to be connected to another detector such as a mass spectrometer in order to determine the mass on the individual peaks. This technique is known as gas chromatography-mass spectrometry or GC-MS. While some GC instruments can be used to purify large quantities of compounds, this is not common practice and they are almost exclusively used as an analytical technique as they are not suitable for large injection volumes.

SAFETY: When injecting a sample solution it is important to

hold the syringe with two hands; one hand holding the barrel and the other positioned behind the plunger. - When manually injecting your sample it is important to remember to clean the syringe with an appropriate solvent, and rinse it with a portion of your sample before using it. The sample should be drawn up into the barrel so that no solution remains in the needle; any solution left in the needle would boil upon contact with the hot metal needle guide. The syringe should be held with two hands; one hand holding the barrel and the other positioned behind the plunger. When injecting samples, be careful not to touch the metal needle guide and not to press the plunger until the needle has pierced the septum.

A gas chromatograph can be used to (more than one answer may be correct)

identify compounds based on their retention times. separate vaporizable compounds. - A gas chromatograph can be used to separate vaporizable compounds. They can determine the purity of products by accurately detecting the presence of any impurities. Furthermore, the percentage composition of a mixture can be determined. Products can be identified by their retention times if there is a known or literature value for comparison. A gas chromatograph needs to be connected to another detector such as a mass spectrometer in order to determine the mass on the individual peaks. This technique is known as gas chromatography-mass spectrometry or GC-MS. While some GC instruments can be used to purify large quantities of compounds, this is not common practice and they are almost exclusively used as an analytical technique as they are not suitable for large injection volumes.

A student is working in the lab and needs some help understanding the IR spectra of his unknown ester in E6. He claims that he carried out all the necessary steps for the workup of his Fischer Esterification, and yet the spectra does not look how he anticipated. Looking through his notebook, you notice some last-minute changes to the procedure. He mistakenly used half the volume of acetic acid and refluxed the reaction for 30 minutes. He neutralized the remaining acid with Na2CO3 and extracted with MTBE. After washing his organic layer with aq. 10% Na2CO3 twice and brine once, he dried the organic phase with anhydrous magnesium sulfate. Next, he removed the MTBE solvent by careful evaporation until the mass was constant. Consider the purpose of each step in the workup, and identify the key mistake, explain what happened as a result, and how this would affect the IR spectra.

issue (a) column chromatography/plug was skipped AND (b) explains results - excess alcohol present (column removes alcohol) AND (c) correctly explains IR data (b) will show extra OH peak at ~3500cm-1

Partners were working on carrying out the separation of hexane and heptane in E5. They didn't pay close attention to the proper set up for their fractional distillation. During distillation, the condenser fell out of the distillation head and knocked over the collection flask, spilling their sample onto their neighbor's hotplate

issue (a) distillation apparatus was not correctly clamped in place, (b) RAMP assessment recognizing risks of experimental setup and flammable solvents (b) There is glassware that can become heated too quickly/break, and the chemicals can escape, posing a hazard to the student because they can inhale/get into contact with chemicals. Doo the experiment in a fume hood/wear PPE, should know where the wash stations and exits are, notify the TA, and have a spill kit for emergencies.

Mario and Luigi are nearing the end of lab during which they have carried out a Fischer esterification. Luigi was quickly cleaning up the fume hood when he grabbed several of what he thought to be clean Pasteur pipettes with his bare hands. However, some liquid in one pipette caused an immediate burning sensation when it contacted his hand. After properly attending to his injury, he asked Mario what could have been on those pipettes. Mario explained how he set the pipette used to transfer concentrated sulfuric acid in the back of the hood. Thinking back, he remarked that there was a lot of acid in the pipette. Identify the safety issues with Mario's waste/lab cleanliness decision and explain how RAMP could have prevented the incident.

issue (a) mario did not immediately clean up/dispose pipettes with H2SO4; Recognizes (b) sulfuric acid is an acute chemical hazard and discusses (c) risk Assessment of exposure probability and/or importance of Minimizing by disposal/lab cleanliness

A student is trying to use Fischer Esterification to prepare some fragrant esters for her aroma diffuser. However, she's having trouble because her reactions is 50% or less and she always has to separate unreacted alcohol and carboxylic acid starting materials present at the end of the reaction. This is problematic because the starting alcohols are expensive. Inspecting her notebook you decide her technique is fine but notice she has been using equal amounts (1:1 stoichiometric ratio) of the starting alcohol and carboxylic acid in her reaction.

issue with yields - Fischer Esterification is thermodynamically neutral (e.g. ∆G~0) with Keq~1 AND (b) using excess carboxylic acid will increase yield and easier purification

Look at #19 E6 Worksheet: A student obtained the following data for his unknown ester product in E6. Observed BP #1: 170C Observed BP #2: 184C Observed BP #3: 190C Use the provided data along the 1:1:1:1 standard to determine the most likely starting alcohol and identify which data best supports her claim I successfully synthesized ______ via Fischer Esterification and thereby identified the unknown starting alcohol as ______. Supporting Data - which data best supports this scientific claim? Consider potential issues with the obtained data that may affect the strength of the claim. What should this data look like to conclusively support the claim? What would make the data inconclusive? The data that best supports the Scientific Claim was ______.

n-Heptyl acetate; 1-heptanol GC data

A liquid is said to be boiling when:

the vapor pressure of the liquid is equal to the atmospheric pressure - When a liquid is heated, the vapor pressure of the liquid increases. Once the vapor pressure is equal to the atmospheric (or applied external) pressure the liquid is said to be boiling.

A liquid is said to be boiling when:

the vapor pressure of the liquid is equal to the atmospheric pressure. - When a liquid is heated, the vapor pressure of the liquid increases. Once the vapor pressure is equal to the atmospheric (or applied external) pressure the liquid is said to be boiling.

Control of heating is essential for successful distillation. If the heat is too high, the vapors will ______ through the fractioning column and maximum separation ______. If the heat is too low, the vapors ______ through the fractioning column and the observed thermometer reading will ______. Thus the rate of distillation is always a compromise between speed and efficiency. Too fast and separation will be ______, too slow and ______. The heating rate is approximated by observing the drop rate of the distillate into the receiver. A good drop rate is around ______. If the drop rate is too fast, the best solution is to quickly ______.

will slowly pass; will occur may not pass; increase poor; you will run out of time 1-2 drops per second lower the lab jack and heating mantle slightly

In Experiment 4, we are using silica gel plates for TLC and silica gel powder for column chromatography. Conduct a RAMP risk assessment for silica gel and write one short sentence for each letter.

•Recognize - Si gel is an inhalation hazard and irritant (harmful). Long term exposure leads to silicosis •Assess - risk of inhalation Minimize - work in hood and/or wear dust mask •Prepare - good suggestions for emergency - i.e. Notify TA and quickly clean up spills to avoid spreading dust, etc.

Experiments 4-7 (Lab)

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