Demon Class w demon teacher pt2

https://docs.google.com/document/d/1X3Zxm7ibrIwtJ-DKWUH_otEfKLLY2UzQiHQ1fpxO7os/edit?usp=sharing From the plot of vapor pressures vs temperature above, estimate the boiling point of heptane when the external pressure is 435 mm Hg.

80 °C 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 435 mm Hg at 80 °C.

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

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

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. X > Y > Z

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

What can you do to elute a compound that is not coming off the column? a. Heat up the column b. Change to a more polar solvent c. Apply air pressure d. Change to a less polar solvent

b. 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.

How much should you fill the reaction flask before refluxing? a. As full as possible. b. Less than half full. c. Over half full.

b. 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.

What are the R f values of the two spots on this TLC plate? Bottom edge to Solvent line: 7.9 Baseline to solvent front: 7.2 Bottom edge to Top edge: 8.4 Baseline to 1st dot: 1.4 1st dot to 2nd dot: 1.6

1.4/7.2 = 0.19 (1.6+1.4)/7.2 = 0.42 The R f 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.

Correlate the microscale procedures needed to accomplish the given steps (1-5) to isolate pure isopentyl acetate (banana oil) from the reaction mixture. 1. This deprotonates unreacted acetic acid, making a water soluble salt. 2. This ensures that the evolution of carbon dioxide gas is complete. 3. This removes byproducts. 4. This removes water from the product. 5. This separates the sodium sulfate from the ester.

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.

Predict the trend in boiling points for the following compounds (1 being the lowest boiling point). a. Water b. Pentane c. Ethanol d. Iso-pentane e. Sodium n-butoxide

4. Water 2. Pentane 3. Ethanol 1. Iso-pentane 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.

https://docs.google.com/document/d/1X3Zxm7ibrIwtJ-DKWUH_otEfKLLY2UzQiHQ1fpxO7os/edit?usp=sharing The infrared spectra for propanol, butanone, and butanoic acid are shown below. Which spectrum belongs to which molecule? assign each molecule to a spectrum

A = Propanol, B = Butanone, C = Butanoic acid Spectrum A has an OH peak (3500 - 3200 cm -1 , broad) but lacks a C=O absorption (1760 - 1665 cm -1 ), so it has to relate to propanol. Spectrum B lacks an OH peak but has a C=O absorption, so it has to relate to butanone. Spectrum C has an OH peak and a C=O absorption, so it has to relate to butanoic acid.

SAFETY: If using plastic joint clips to stabilize your equipment, which clips in the diagram should NOT be used?

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

Which key reagents would you need to use to distinguish between following two molecules? secondary alcohol and primary alcohol A. Silver nitrate and ammonium hydroxide B. Anhydrous zinc chloride and hydrochloric acid C. Chromic acid D. 2,4- dinitrophenyl hydrazine

B. Anhydrous zinc chloride and hydrochloric acid Lucas test test positive for secondary alcohol and negative for primary alcohol

Which of the peaks in the infrared spectrum for ethyl acetate is for the carbonyl (C=O) functional group? strong peak at 1700

B. strong peak at 1700 Carbonyl peaks are strong, sharp absorptions between 1760 - 1665 cm -1 .

What reagent (or compound) causes the observed visual change in a positive Lucas test? A. The product hydrazone is insoluble. B. Ag(I) is reduced to Ag(0) C. The alkyl halide product is insoluble in water D. Cr(VI) is reduced to Cr(III)

C. The alkyl halide product is insoluble in water

Which functional group can give a false positive for the Jones test? A. Phenols B. 3° alchohol C. Ketone D. Aldehyde

D. Aldehyde

Explain this order of elution. Gas chromatography separates compounds depending on their (polarity/volatility/polarity and volatility). Benzene, m-xylene, and toluene have similar (volatilities/polarities), therefore, the main basis for separation is (polarity/volatility). The more volatile a component the (lesser/greater) its vapor pressure, hence the more time it spends in the (gaseous/solid) mobile phase, giving it a (longer/shorter) retention time. Therefore, components of a liquid mixture will elute in order of (decreasing/increasing) 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.

https://docs.google.com/document/d/1X3Zxm7ibrIwtJ-DKWUH_otEfKLLY2UzQiHQ1fpxO7os/edit?usp=sharing Using the phase diagram, determine the molar composition of the vapor in equilibrium with a boiling liquid that has a composition of 20.% A and 80.% B. Percentage vapor composition A = ___% Percentage vapor composition B = ___% What is the boiling point of this liquid? Boiling point = ___°C

Percentage vapor composition A = 55% Percentage vapor composition B = 45% Boiling point = 140°C * when I did the chart it looks like it should be 145 °C but the hw program says it's 140 °C The molar composition of the vapor in equilibrium with a boiling liquid that has a composition of 20.% A and 80.% 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 20. % (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.

If you separated a mixture of benzene, toluene, and m-xylene by gas chromatography, what would be the expected order of retention times? Shortest time → Longest Time

The order of retention times is as follows: Shortest retention time→Longest retention time Benzene → Toluene → m-Xylene

Complete the following paragraph. The stationary phase in TLC is (polar/non-polar). Therefore, the (more/less) polar component of the mixture will travel a greater distance up the plate, resulting in a (higher/lower) Rf value for the component. When separating a mixture containing bromobenzene and p-xylene, the (bromobenzene/p-xylene) spot would be expected to travel the greatest distance up the plate as it is the (more/less) polar component. The (bromobenzene/p-xylene) would travel the least distance as it is the (more/less) polar component.

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 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 False

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 False

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

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? a. 1760-1665 b. 3100-3000 c. 3500-3200 d. 800-500

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

If you wanted to prevent moisture from the air getting into your reaction, how could this be achieved? a. Attach a tube containing a drying agent, such as Drierite, in the top of the condenser. b. Attach the top of the condenser to a vacuum source. c. Put a stopper in the top of the condenser.

a. Attach a tube containing a drying agent, such as Drierite, in the top of the condenser. A drying tube can be attached to the top of the condenser to keep the atmosphere free of water vapor. The top of the condenser should never be stoppered, as this creates a sealed system that will pressurize when the liquid starts to boil and could cause an explosion.

SAFETY: Which of the following statements about the procedure for column chromatography are true? More than one answer may be correct. a. Check for cracks in the glass before pressurizing the system. b. Apply enough pressure to increase the flow rate to a reasonable degree. c. Release the pressure rapidly to slow down the flow of solvent. d. Clamp the column loosely. e. Apply as much pressure as possible.

a. Check for cracks in the glass before pressurizing the system. b. Apply enough pressure to increase the flow rate to a reasonable degree. 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.

Which of the following solvents would be the best to separate a mixture containing bromobenzene and p-xylene by TLC? a. Acetone b. Hexane c. Methylene chloride d. None of the above

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

Why is it useful to be able to determine the boiling point of a compound? More than one answer may be correct. a. It can be used to determine the purity of a product. b. It can be used to help purify products. c. It can be used to help identify unknown compounds.

a. It can be used to determine the purity of a product. b. It can be used to help purify products. c. It can be used to help identify unknown compounds. 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.

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. a. It requires the smallest volume of sample. b. Once you have two results that are within 2 °C of each other you do not need to perform another boiling point determination. c. Once bubbles are expelled slowly from the capillary tube, turn the heat off; the liquid has boiled. d. Heating the sample rapidly gives the most accurate measurement. e. Heat should only be applied to the side arm of the Thiele tube. f. 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.

a. It requires the smallest volume of sample. e. Heat should only be applied to the side arm of the Thiele tube. f. 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 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 statements concerning the principle of separation in gas chromatography is true when using a liquid stationary phase? (More than one answer may be correct.) a. 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. b. 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. c. Separation is always based on the boiling points of the compounds alone. d. The vapor pressure of a compound is independent of temperature.

a. 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. b. 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.

What is the effect of using a longer column? a. The separation will be more effective, as the sample undergoes more partitioning between the mobile and stationary phases. b. The sample will start to react with the carrier gas. c. The sample won't have a chance to equilibrate with the stationary phase, leading to poor separation. d. The sample will start to react with the column.

a. 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.

When performing a fractional distillation, how can you tell when your liquid is beginning to distill over? More than one answer may be correct. a. The temperature remains constant after initially rising. b. The temperature starts to rise as measured by the thermometer. c. Liquid droplets start to condense on the thermometer bulb.

a. The temperature remains constant after initially rising. c. Liquid droplets start to condense on the thermometer bulb. 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.

Which of the following is an appropriate use for reflux? a. To carry out a reaction that needs heating. b. To prepare a sample for filtration. c. To remove the solvent from a reaction mixture.

a. To carry out a reaction that needs heating. Use reflux for reactions that require heating and contain volatile solvents, reactants, or products.

Which of the following is an appropriate use for distillation apparatus? More than one answer may be correct. a. To measure a boiling point of a liquid. b. To remove a liquid from a reaction mixture, allowing collection of an insoluble product. c. To remove a liquid product from a reaction mixture.

a. To measure a boiling point of a liquid. c. 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.

Why should the cold end of the apparatus be open to the atmosphere in a distillation set-up? a. To prevent pressure build up, which could cause an explosion. b. To allow air in to replace the vapor from the boiling liquid. c. To allow air in to further cool the system.

a. 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.

A gas chromatograph can be used to (more than one answer may be correct) a. determine the purity of a product. b. determine the percentage composition of a mixture. c. purify large quantities of compounds. d. determine the mass of a compound. e. separate nonvolatile compounds.

a. determine the purity of a product. b. determine the percentage composition of a mixture. 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.

AFETY: When using an aluminum heating block with an electric hot plate it is important to (more than one answer could be correct) a. fit the aluminum block with a digital thermometer to monitor the temperature. b. hover your hand above the heating block to check whether it is hot. c. leave the flask in the aluminum block to cool back to room temperature. d. fit the aluminum block with a glass mercury thermometer to monitor the temperature. e. touch the aluminum block with the back of your hand to check if it is hot. f. not leave the reaction unattended until the set temperature has been reached and the temperature remains stable.

a. fit the aluminum block with a digital thermometer to monitor the temperature. b. hover your hand above the heating block to check whether it is hot. f. not leave the reaction unattended until the set temperature has been reached and the temperature remains stable. It is important to select the appropriately sized aluminum block to fit the round bottom flask snugly and also to secure glassware using a clamp and clamp stand. Glass mercury thermometers should not be used as they can break when in direct contact with the heating block releasing toxic mercury vapours. A digital thermometer should be used instead to monitor the temperature. Never touch the heated aluminum block directly with your hand, you can check to see if it's hot by passing your hand over it. It is very important to remain with your reaction until it has reached the temperature that you have set to ensure that the temperature is stable and doesn't become too low or too high. You shouldn't leave the reaction flask to cool in the aluminum block. As the heating block cools down it can contract and break the flask.

SAFETY: When using a heating mantle make sure (more than one answer might be correct) a. that there is a temperature control unit connected before plugging the heating mantle into mains electricity. b. you use a lab jack to elevate and lower the heating mantle to and away from the glassware in use. c. you choose a heating mantle that can accommodate your flask snugly. d. you turn the heating mantle off as soon as you have finished using it. e. to allow the heating mantle to cool before turning it off. f. you select a heating mantle much larger than your reaction flask.

a. that there is a temperature control unit connected before plugging the heating mantle into mains electricity. b. you use a lab jack to elevate and lower the heating mantle to and away from the glassware in use. c. you choose a heating mantle that can accommodate your flask snugly. d. you turn the heating mantle off as soon as you have finished using it. If you are using a heating mantle that doesn't have a built in controller, you must never plug it directly into the mains because you will have no way of regulating the temperature. The heating mantle should fit your round bottom flask snugly to ensure even heating of the contents. A lab jack should be used to raise and lower the heating mantle as this enables the heat source to be removed quickly if overheating occurs. You should always turn off the heating mantle as soon as you have finished using it.

SAFETY: When removing solvent using open-vessel evaporation, (more than one answer may be correct) a. the procedure must be carried out in a fume cupboard. b. the procedure can be carried out on the work top. c. you can evaporate solutions to dryness. d. you do not need to stir the solution.

a. the procedure must be carried out in a fume cupboard. c. you can evaporate solutions to dryness. d. you do not need to stir the solution. In open-vessel evaporation the solvent vapors escape into the air, therefore, the procedure must always be performed in a fume cupboard to prevent inhalation of harmful vapors.

A liquid is said to be boiling when: a. the vapor pressure of the liquid is equal to the atmospheric pressure. b. the liquid is bubbling vigorously. c. the vapor pressure of the liquid reaches 1 atm. d. the rate of molecules leaving the liquid surface is the same as the rate of the molecules returning.

a. 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.

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.

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

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.

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

What rate should the liquid come across in a fractional distillation? a. One or two drops per second. b. A few drops per minute. c. In a steady stream.

b. A few drops per minute. 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.

Which is the best description of a fractional distillation? a. A variation of simple distillation that requires collecting lots of different fractions. b. A technique to separate liquid mixtures with boiling points close to each other.

b. 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.

What is a good R f value in order to ensure that a compound will elute over a reasonable timeframe? a. Close to 1 b. Around 0.3 c. Close to zero d. Around 0.7 e. Around 0.5

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

SAFETY: Which statement best describes how the system should be heated? a. Boil as vigorously as possible. b. Heat gently so that the solvent boils and the vapors extend no more than half way up the condenser. c. Heat gently so that the solvent boils and the vapors reach the full height of the condenser. d. Do not allow the solvent to boil.

b. Heat gently so that the solvent boils and the vapors extend no more than half way up the condenser. The height of the vapor can be seen as a ring within the condenser. This should not extend beyond half way up the condenser and preferably lower to ensure no vapor is lost from the system.

The infrared region between 3650 cm -1 and 2650 cm -1 is shown for a molecule. What functional group does the molecule contain? broad tongue 3450-3250 a. Carbonyl (C=O) b. Hydroxyl (-OH) c. C-H d. Double bond (C=C) e. Secondary amine (-NHR) f. Primary amine (-NH 2 )

b. 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.

SAFETY: Which of these are safety concerns related to the use of UV light to expose spots on a TLC plate? a. It may stain your skin. b. It can damage your eyes if looked at directly. c. It can cause burns. d. It should not be inhaled.

b. 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 the best description of a reflux? a. Reflux is a separation technique. Any liquid that has a boiling point different to others in a mixture can be heated, turned to a gas, and condensed in a different part of the apparatus. b. Reflux is a technique used to heat volatile materials. The reaction vessel is fitted with a condenser so that any vapors from the flask fall back into the heated mixture.

b. Reflux is a technique used to heat volatile materials. The reaction vessel is fitted with a condenser so that any vapors from the flask fall back into the heated mixture. Reflux is often used in reactions that require heating over an extended period of time. Reflux allows the contents of the flask to be heated without a build-up of pressure (as the system is open to the atmosphere), while preventing the contents of the flask from escaping.

Why should the solvent level in the elution tank be below the level of the baseline of the TLC plate? a. It provides a better surface area (as more of the paper is exposed). b. The compound in the spots would dissolve into the solvent if it were higher. c. This provides about the right amount of solvent for a TLC. d. It provides the maximum amount of TLC for the spots to run on.

b. 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.

Why shouldn't the start line, where the solution mixtures are initially placed, be drawn in ink? a. The ink will bond with the sample, not allowing it to move up the plate. b. The ink is likely to dissolve in the solvent and will add extra spots to the chromatogram. c. You cannot write on alumina or silica with ink. d. Pencil lines look neater.

b. 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.

SAFETY: Why is it important to handle silica powder in a fume cupboard? More than one answer may be correct. a. It prevents contamination of the silica powder. b. The powder, if inhaled, can cause serious problems to the respiratory tract. c. The powder is fine and easily inhaled. d. It allows for any spills to be easily contained.

b. The powder, if inhaled, can cause serious problems to the respiratory tract. c. The powder is fine and easily inhaled. Silica powder can be carcinogenic if inhaled. It is a very fine powder that readily forms clouds of dust that are easily inhaled.

IR spectroscopy can be used to determine which of the following? More than one answer may be correct. a. The molecular mass of a sample. b. The presence of certain bonds within a molecule. c. The absence of certain groups from a molecule. d. The presence of impurities in a product

b. The presence of certain bonds within a molecule. c. The absence of certain groups from a molecule. d. The presence of impurities in a product 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 happens if the spots are made too small when preparing a TLC plate for development? a. Additional spots will appear on the plate, interfering with analysis. b. The spots will be difficult to see after development. c. The spot material will dissolve off the plate. d. The spots will saturate the plate, show tailing, and/or diffuse into one another.

b. The spots will be difficult to see after development. If the initial spots are made too small there will be even less material in the separated spots, making them difficult or impossible to see after development.

What is the reason for the layer of sand at the bottom of the column? a. To filter the solvent before collection b. To prevent the adsorbent from passing through to the tap c. To show where the bottom of the adsorbent column is

b. 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.

Two liquids have boiling points which are less than 20 °C apart. How can a simple distillation be modified to improve the separation? a. Heat very gently. b. Use a fractionating column. c. Use very cold water in the condenser.

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

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. a. When the sample enters the column, the compounds form chemical bonds with the stationary phase. b. When the sample enters the column, the compounds dissolve to varying extents in the stationary phase. c. The extent to which a molecule interacts with the stationary phase depends on its size. d. Enantiomers can be separated by gas chromatography because they have different boiling points.

b. When the sample enters the column, the compounds dissolve to varying extents in the stationary phase. c. 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. a. How quickly you heat the liquid. b. Whether a compound is polar or not. c. The pressure. d. The amount of liquid you have.

b. Whether a compound is polar or not. c. 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.

SAFETY: TLC spotters are sharp. The MAJOR safety concern when using spotters is that: a. they can damage the TLC plate. b. they can cause stab injuries. c. they can create large spots on the TLC plate if you are not careful. d. they are hot and can cause burns.

b. they can cause stab injuries. Spotters are sharp and can cause stab injuries.

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? a. 800-500 b. 1760-1665 c. 3500-3200 d. 3100-3000

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

What features make a sample suitable for analysis by gas chromatography? (More than one answer may be correct.) a. Thermal instability. b. High boiling point. c. Appreciable volatility. d. Thermal stability. e. High vapor pressure.

c. Appreciable volatility. d. Thermal stability. e. High vapor pressure. 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.

Where should the thermometer bulb be during a distillation? a. Just above the boiling liquid. b. In the liquid. c. At the mouth of the condenser.

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

SAFETY: How much should you fill your distillation pot? a. Over half full. b. As full as possible. c. Less than half full.

c. 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.

SAFETY: Where should the reflux equipment be clamped? a. Securely at the top of the condenser b. Securely at the top of the condenser and the neck of the flask c. Securely at the neck of the flask

c. Securely at the neck of the flask The equipment should be secured at the neck of the flask. Any extra clamping of the condenser may cause the joint between the flask and the condenser to be compromised, allowing vapor to escape.

In a vacuum distillation, what is the effect of using reduced pressure? a. The boiling point of the fractions are increased b. There is no change in the boiling points of the fractions c. The boiling point of the fractions are decreased

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

What observation would you expect to make if a primary or secondary alcohol reacted with acidified potassium dichromate(VI) solution? a. The green solution turns colorless. b. The green solution turns orange. c. The orange solution turns green. d. The orange solution turns colorless.

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

What is the consequence of the gas flow rate being too high? a. The peaks will broaden due to the diffusion of the compounds in the gas phase. b. The sample will start to react with the gas flow. c. The sample won't have a chance to equilibrate with the stationary phase, leading to poor separation. d. The sample will irreversibly bind to the column. e. The sample will start to react with the column.

c. 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.

Why might you want to heat a reaction? More than one answer may be correct. a. To evaporate the solvent more quickly. b. To decrease the rate of the desired reaction. c. To overcome the activation energy for the reaction. d. To increase the solubility of the reagents. e. To increase the rate of the reaction.

c. To overcome the activation energy for the reaction. e. To increase the rate of 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. You would not usually want to remove the solvent during the reaction. To make sure this doesn't happen you need to fit the reaction flask with a condenser and check all glass joints are tightly sealed. Adding additional solvent would be preferable to heating a reaction mixture to aid solubility.

SAFETY: When derivatizing an alcohol with trimethylsilyl chloride, you should: a. carry out the reaction on the bench top. b. clean up any spillages with water. c. Wear a lab coat, glasses and gloves. d. rinse the glassware with water before use. e. heat with a Bunsen burner.

c. Wear a lab coat, glasses and gloves. 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.

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? a. 800-500 b. 1760-1665 c. 3500-3200 d. 3100-3000

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

https://docs.google.com/document/d/1X3Zxm7ibrIwtJ-DKWUH_otEfKLLY2UzQiHQ1fpxO7os/edit?usp=sharing What is the significance of the horizontal line between points X and Y? a. The point X gives the vapor composition of the less volatile component and Y gives the vapor composition of the more volatile component. The line gives the difference. b. A boiling liquid with composition Y will produce a vapor with composition X. c. The length of the line XY corresponds to the difference in boiling point of components A and B. d. A boiling liquid with composition X will produce vapor with composition Y.

d. A boiling liquid with composition X will produce vapor with composition Y.

What characteristic odor would you expect to observe if an alcohol reacted with acidified ethanoic acid? a. A vinegar-like smell. b. A rotten fruit smell. c. None. The product would be odorless. d. A fruity smell.

d. A fruity smell. The test for an alcohol uses acidified ethanoic acid. A positive test results in the production of an ester, which has a characteristic fruity smell.

SAFETY: A risk assessment for a reaction should include the hazards associated with the: a. procedures involved. b. chemical reagents used. c. chemical products and by-products. d. All of the above.

d. All of the above. A risk assessment should include the hazards associated with the procedures involved, the chemical reagents used, and the chemical products.

SAFETY: While setting up a micro-boiling point determination you accidently break a capillary tube. You should: a. Leave it in your fume cupboard. b. Put it in your pocket, if your instructor sees that you have broken it they will be angry. c. Put it in the trash. d. Dispose of it in the appropriate glass waste container.

d. 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.

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? a. Steam distillation b. Vacuum distillation c. Fractional distillation d. Simple distillation

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

When setting up a column, what is the reason for adding a layer of sand on top of the adsorbent column? a. To filter the solvent b. To stop the solvent from dissolving the sample c. To do the first part of the separation d. To prevent disruption of the surface when solvent is added

d. 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.

How long should you run a TLC plate for? a. Until the solvent front is about half way up. b. Until the solvent front is at the top of the plate. c. 10 minutes. d. Until the solvent front is just below the top of the plate. e. 2 minutes.

d. 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.

Which of the following would give you the most accurate mass of your compound? a. Using a top-loading balance and weighing by difference. b. Using an analytical balance and the "Tare" button to set the weight of the crucible to zero. c. Using a top-loading balance and the "Tare" button to set the weight of the crucible to zero. d. Using an analytical balance and weighing by difference.

d. Using an analytical balance and weighing by difference. Top-loading balances give mass to the nearest 0.1-0.001 g, depending on the model, whereas analytical balances give mass to the nearest 0.0001 g. Analytical balances should be used for accurate mass measurements. Weighing by difference removes the error associated with a particular balance, hence increasing the accuracy.

When setting up a fractional distillation, the main difference from a simple distillation is: a. You need to heat more vigorously. b. You use an ice bath below the collection flask. c. You collect more slowly. d. You need to add a column between the flask and the distillation head.

d. 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.

SAFETY: When injecting a sample solution it is important to a. push the plunger as soon as the needle goes through the metal needle guide. b. hold the syringe at the plunger end with only one hand to minimize the risk of burning yourself on the metal needle guide. c. fill the syringe, including the needle. d. clean the syringe with an appropriate solvent and rinse through with a portion of your sample before using it. e. hold the syringe with two hands; one hand holding the needle steady and the other hand holding the barrel.

d. clean the syringe with an appropriate solvent and rinse through with a portion of your sample before using it. 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.

What type(s) of intermolecular forces are expected between CH3OH molecules? dipole forces (Y/N) induced dipole (London dispersion) forces (Y/N) hydrogen bonding (Y/N)

dipole forces (Y) induced dipole (London dispersion) forces (Y) hydrogen bonding (Y) Induced dipole forces are always present. Induced dipole forces are also called dispersion forces, or London forces.CH3OH is a polar molecular compound. Therefore, the intermolecular forces also include dipole forces.Hydrogen bonding is found in situations represented by D-H---A where both the donor atom, D, and the acceptor atom, A, are one of the highly electronegative elements O, N, or F. CH3OH falls into this category.

SAFETY: How should the silica be disposed of at the end of the experiment? a. In the appropriate waste solvent container for the solvent used. b. In the non-chlorinated waste solvent. c. In a laboratory bin. d. In the chlorinated waste solvent. e. In the appropriate waste solid container.

e. 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.

In silica gel chromatography, which compounds elute first? a. Those with the highest molecular weight b. The most polar c. Those with ionic functional groups d. Those with the lowest boiling point e. The least polar

e. 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.

Observing the formation of a silver mirror on the surface of a test tube when using Tollen's reagent indicates the presence of: a. an alcohol. b. an alkene. c. a ketone. d. an aldehyde or ketone. e. an aldehyde.

e. 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.

The infrared band below is broad (about 200 cm -1 wide) and shows a characteristic double peak. Which functional group is present in the molecule? Fangs 3450-3250 a. Carbonyl (C=O) b. Hydroxyl (-OH) c. C-H d. Double bond (C=C) e. Secondary amine (-NHR) f. Primary amine (-NH 2 )

f. Primary amine (-NH 2 ) A broad peak between 3400 - 3200 cm -1 is indicative of a primary amine group (-NH 2 ). Broader, U- or V-shaped peaks between 3600 - 3100 cm -1 are indicative of an -OH group. The double peak shows that the amine is primary and not secondary.