Term
| Why should you not use a solvent (other than water) to remove chemicals from your skin? |
|
Definition
| 1) This will hasten the absorption of chemicals through the skin |
|
|
Term
| Why is it important to prevent a person with burning clothing from running? |
|
Definition
| 1) The greatest harm from a fire comes from breathing the hot vapors that rise past the mouth |
|
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Term
| How should a fire extinguisher be directed when trying to put out a fire? |
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Definition
| 1) Aim it at the base of the fire and squeeze the handle (but don't squeeze too long because the handle will become cold) |
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Term
| A very small fire in a beaker or a flask could possibly be put out by simply covering the vessel with a flat object. Why is this possible? |
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Definition
| 1) A wire gauze or watch glass could put out a small fire because it will cut of the supply of oxygen which fuels the fire |
|
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Term
| Why is it dangerous to wear contact lenses in the organic chemistry lab (be specific)? |
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Definition
| 1) The lenses could fuse to one's eyes |
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Term
| Why would placement of too much sample into a melting point capillary tube cause an inaccurate melting point to be observed? |
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Definition
| 1) Too much will cause differentials in the temperature throughout the sample |
|
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Term
| Why would coarse particles in a melting point sample cause an inaccurate melting point to be observed? |
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Definition
| 1) Coarse particles will cause air pockets which will cause an inaccurate temperature. |
|
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Term
| Define eutectic point in terms of the two components of a mixture and their liquid solutions. |
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Definition
| 1) The point at which x and y and their liquid solutions are in equilibrium |
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Term
| You have carried out an experiment that has produced a new unknown compound Y. Which of the three reasons for a melting point determination would best describe why you would take the melting point of compound Y? |
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Definition
1) To characterize the unknown compound
2) To record a physical characteristic of the new compound
3) To establish the purity of the compound (impurity will have a lower and wider range of temperatures) |
|
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Term
| Define eutectic point with respect to the melting point composition diagram. |
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Definition
| 1) The lowest point on a graph in which the mixture reaches a narrow point |
|
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Term
| List three effects of the recrystallization process on the melting point (range) of a solid. |
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Definition
1) Cause a narrower melting point range
2) Purify it
3) Melting point range will be displaced upward |
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Term
| Anthracene has a much higher melting point than napthalene. What is the main reason for the higher melting point in anthracene? |
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Definition
| 1) Anthracene has more conjugated double bonds |
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Term
| In the "Hints for Preparation" you were instructed to make sure that the temperature of the Mel-Temp apparatus was 80 degrees Celsius or lower before inserting a sample of pure urea (melting point 132.5-133 degrees Celsius) into the slot in the Mel-Temp. Why was it important that the Mel-Temp temperature be so much lower than the sample's melting point to get an accurate melting point (be specific)? |
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Definition
| 1) The tube must be heated slowly and gradually in order to get an accurate measurement of the melting point |
|
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Term
| What condition does a solid impurity have to satisfy in order to depress a compound's melting point? |
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Definition
| 1) The solid impurity needs to be soluble |
|
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Term
| The melting point of a pure compound is where the __________ __________ of the solid and liquid are equal. |
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Definition
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Term
| How do you ensure that the cooling of the crystal solution occurs slowly? |
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Definition
1) Don't move or disturb the solution as it's cooling. If it is moved, then too many nuclei will form crystals and impurities will come out
2) Use a paper towel to insulate the test tubes and place it in a beaker |
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Term
| What is the remedy if too much solvent is used in the recrystallization process and no material crystallizes? |
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Definition
| 1) Evaporate the solvent to the point of saturation |
|
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Term
| What may happen if a boiling chip or boiling stick is not added to a hot solution? |
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Definition
| 1) May become super-heated or boil over |
|
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Term
| List two ways one can induce crystallization in a supersaturated solution. |
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Definition
1) Use seed crystals
2) Scratch bottom of test tubes with a glass rod |
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Term
| How do you ensure that you form a saturated crystallizing solution in the process of recrystallization? |
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Definition
| 1) You should dissolve the minimum amount of hot solvent and use a boiling chip |
|
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Term
| Why would a eutectic point be difficult to detect? |
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Definition
| 1) An impurity could cause the mixture to begin melting at a temperature lower than the eutectic point |
|
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Term
| Why is it important to use filter paper on the frit of the Hirsch funnel apparatus? |
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Definition
| 1) So the frit will not become clogged with insoluble purities |
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Term
| You used methanol-water as your solvent pair to recrystallize benzoic acid. Between methanol an water, which is the better solvent? Which is the poorer solvent? |
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Definition
| 1) Methanol is the better solvent because it will dissolve molecules of a higher polarity |
|
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Term
| Why is it important to dry the crystals obtained from a recrystallization? How does one complete the drying of crystals after the crystals have stayed on the Hirsch funnel and before they are transferred to a watch glass? |
|
Definition
1) Solvent can be an impurity and affects the melting point
2) Pass product on the filter to remove the solvent. Then remove it from the filter paper to remove the solvent. |
|
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Term
| In the collection of crystals step, why is vacuum filtration used instead of gravity filtration? |
|
Definition
| 1) Vacuum is more efficient in removing the solvent from crystals |
|
|
Term
| Why is vacuum filtration not employed to filter suspended solids in the recrystallization process? |
|
Definition
| 1) The hot solvent will cool during the process and the product will crystallize in the filter |
|
|
Term
| Why is it important to remove the boiling stick from the hot crystal solution before crystallization begins? |
|
Definition
| 1) So the crystals don't form on the stick |
|
|
Term
| Why is the washing step necessary in the recrystallization process? |
|
Definition
| 1) To wash off any impurities |
|
|
Term
| List the two reasons why large crystals are preferred when recrystallizing a solid. |
|
Definition
1) Easily separated by filtration
2) Easily washed free of adhering impure solvent |
|
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Term
| If 28 grams of an organic solid is dissolved in 60 mL of water, how many grams remain in the water after extraction with 40 mL of a solvent which has a partition (distribution) coefficient with water of 12? Show calculations. |
|
Definition
1) 12 = (x/40mL)/[(28-X)/60mL]
2) 60X/(1120-40X) = 12/1
3) 540X = 13440
4) 24.9g
5) 28 - 24.9g = 3.1g |
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Term
| In the experiment you are carrying out today, why do you add saturated sodium chloride to the tube that now only contain biphenyl in ether? |
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Definition
| 1) It removes the water from the ether to the aqueous layer (functions as a drying agent) |
|
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Term
| What is the problem of shaking a test tube with a stopper to mix the aqeuous and organic layer in the extraction experiment? |
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Definition
| 1) The high vapor pressure of the solvent will often force the liquid out around the cork or stopper |
|
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Term
| Why do you add concentrated HCl to the aqueous layer obtained when the mixture of 4-tertbutylphenol and biphenyl ether is mixed with aqueous sodium hydroxide? |
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Definition
| 1) This is to neutralize the NaOH and form a compound to be water soluble |
|
|
Term
| Why do you add concentrated HCl to the aqueous layer obtained when the mixture of benzoic acid, 4-bromophenol and biphenyl ether is mixed with the aqueous sodium bicarbonate? |
|
Definition
| 1) To regenerate benzoic acid |
|
|
Term
| In the extraction experiment, how do you ensure that all your extract has been transferred from the drying agent after the organic layer is dried? |
|
Definition
| 1) Wash the drying agent with ester |
|
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Term
| You dissolve a mixture of phenol (weak acid), aniline (a base), and napthalene (neutral compound) in ether. You extract the mixture with NaOH. What is contained in the organic layer? What is contained in the aqueous layer? (Use actual names of compounds in each layer). |
|
Definition
1) Organic layer: Napthalene and aniline
2) Aqueous layer: Sodium phenoxide (ionic compound) and water |
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Term
| You dissolve a mixture of aniline (a base) and napthalene (a neutral compound) in ether. You extract the mixture with HCl. What is contained in the organic layer? In the aqueous layer? (Use actual names of species in each layer). |
|
Definition
1) Organic layer: Napthalene
2) Aqueous layer: Anilinium chloride |
|
|
Term
| In the separation of benzoic acid, 4-bromophenol, and biphenyl, what would occur if sodium hydroxide is used in the first extraction? |
|
Definition
| 1) It will extract both benzoic acid and 4-bromophenol |
|
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Term
| Why was there bubbling when HCl was added to the aqueous extract containing sodium benzoate? (Explain what HCl was extracting with cause to bubbling). |
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Definition
| 1) CO2 vapors were trying to escape the solution while HCl reacted with NaHCo3 to produce H20 and CO2 |
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Term
| When you added HCl to the aqueous layer containing sodium benzoate, bubbling occurred. Why did you NOT see bubbling when you added HCl to the aqueous layer containing sodium-4-bromophenoxide? (Compare the two situations). |
|
Definition
1) CO2 vapors were trying to escape the solution. HCl reacted with NaHCO3 to produce H20 and CO2
2) Excess NaOH doesn't produce CO2 like excess NaHCO3 does when reacted with HCl |
|
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Term
| List two ways to prevent / remedy emulsions. |
|
Definition
1) Make the aqueous layer ionic by adding concentrated NaCl as well as dissolving and shaking the tube
2) Shake the solution to be extracted gently until the layer separates readily. |
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Term
| In the extraction steps, you find that you do not recover 100% of the compound you are extracting. Why is that? |
|
Definition
| 1) Some of the compound is lost when pipetting and transferring into the vial or watch glass |
|
|
Term
| List two observations that indicate that enough drying agent was added to the organic layer (assume the drying agent is a powder). |
|
Definition
1) Drying agent does not clump (clumping reveals the presence of water)
2) The wet organic layer is no longer cloudy (becomes clear) |
|
|
Term
| Why is it important that the organic solvent for extraction have a low boiling point? |
|
Definition
| 1) So it can easily evaporate and leave behind the product |
|
|
Term
| One of the uses of TLC is to determine the number of components in a mixture. What does this help in achieving? |
|
Definition
| 1) Helps in the further planning of analytical and separation steps |
|
|
Term
| One of the uses of TLC is to monitor the progress of a reaction. What kind of information does TLC provide in this instance? |
|
Definition
1) Optimum time to halt the reaction
2) The effect of changing such variables such as temperature, concentration, and amount of solvent can occur without having to isolate the product |
|
|
Term
| You carry out a TLC on a solid after you recrystallize it. What is the purpose of TLC in this instance? |
|
Definition
| 1) TLC can determine the purity of the compound |
|
|
Term
| How can TLC be used to determine the appropriate conditions for a column chromatographic separation? |
|
Definition
| 1) The correct absorbent and solvent used to carry out the chromatography can be determine rapidly by TLC |
|
|
Term
| How is TLC used to monitor column chromatography? |
|
Definition
| 1) TLC determines which factions have the desire components of the mixture |
|
|
Term
| Why is it important to have a filter paper in the developing chamber in the TLC experiment? |
|
Definition
| 1) The filter paper helps to saturate the chamber with solvent vapors. This helps the solvent to rise up the TLC plate by capillary action effectively |
|
|
Term
| What precaution does one have to take when marking a TLC plate before it is spotted? |
|
Definition
| 1) Draw the line lightly in order to avoid flaking off the absorbent. If flaked, the solvent will not rise up the plate effectively. |
|
|
Term
| Why is it important that the top of the chromatography jar be kept on while developing a TLC plate? |
|
Definition
| 1) If the top is not kept on the solvent will evaporate which causes the TLC plate to become messy and ineffective |
|
|
Term
| List two precautions that one has to take in order to ensure that the initial spot on a TLC plate does not streak during the developing stage. |
|
Definition
1) Make spots small and compact by touching the plate lightly with the capillary
2) Sample should not be extremely concentrated |
|
|
Term
| Why is it important that the level of the solvent in the developing chamber be below the spotting line? |
|
Definition
| 1) The solvent can dissolve the compound if it is near the spotting line |
|
|
Term
| Why is it important to remove the TLC plate from the developing chamber as soon as the solvent reaches the solvent front? |
|
Definition
| 1) Spots in visualization stage will be difficult to evaluate |
|
|
Term
| Why should one not stick the capillary tube (spotter) directly into the reagent bottle? |
|
Definition
| 1) It will contaminate the reagent |
|
|
Term
| In the TLC experiment, what might occur if you use silica as your adsorbent to distinguish between a set of very non-polar solutes? |
|
Definition
| 1) There will be a very high Rf value because non-polar compounds will travel with the solvent front when silica is used |
|
|
Term
| In the TLC experiment what would be the issue if the adsorbent is flaked off before the TLC plate is developed? |
|
Definition
| 1) The solvent will not rise up the TLC plate effectively |
|
|
Term
| In the distillation reaction, what step can you take to ensure that vapor does condense in the side arm of the condenser? |
|
Definition
| 1) Place a wet paper towel around the side arm |
|
|
Term
| How does one control the heat input to the distillation apparatus in the experiment that you are carrying out? |
|
Definition
| 1) By shifting the sand in the sand bath away from or closer to the reaction flask |
|
|
Term
| What is the purpose of insulating the fractioning column? |
|
Definition
|
|
Term
| Why is the rate of distillation important in fractional distillation? |
|
Definition
| 1) The rate must be slow so that ascending vapors and descending liquids achieve equilibrium |
|
|
Term
| Why is it important that the end of the sidearm of the Claisen head be inside the receiving flask in the distillation experiment? |
|
Definition
| 1) To minimize the release of vapors into the hood (loss of liquid) |
|
|
Term
| In the distillation experiment, why is it important not to heat in a closed container? |
|
Definition
|
|
Term
| In the distillation apparatus setup, why is it important that the thermometer bulb be placed completely below the side arm of the Claisen head? |
|
Definition
| 1) So it accurately records the temperature of the vapor distilling through the sidearm |
|
|
Term
| In the distillation experiment, why does a boiling chip become ineffective after it is used once? |
|
Definition
| 1) As the chip cools liquid fills the capillaries in which air previously resided |
|
|
Term
| Why is it important not to distill liquids to dryness? |
|
Definition
| 1) The dry residue of the liquid can be explosive |
|
|
Term
| What does HETP (as it is related to fractional distillation) stand for? How do HETP and the efficiency of fractionating columns relate to each other? |
|
Definition
1) HETP stands for High Equilibrium Thermometer Plate
2) The lower the HETP, the more efficient the column |
|
|
Term
| In steam distillation, what requirement is necessary in order for the boiling point of the mixture to remain constant? |
|
Definition
| 1) The boiling point remains constant during a steam distillation as long as adequate amount of water and the organic components are present to saturate the vapor space |
|
|
Term
| What is the problem that may arise if the packing material for fractional distillation has too large a surface area? |
|
Definition
| 1) The column will absorb much of the material being distilled |
|
|
Term
| What is the problem that arises if too dense a packing material is used for fractional distillation? |
|
Definition
| 1) Pressure changes take place within the column causing non-equilibrium conditions |
|
|
Term
You must know what kinds of alkyl halides will react (will form precipitate) with:
1) Sodium iodide in acetone
2) Silver nitrate in ethanol |
|
Definition
1) Polar aprotic (SN2)
2) Polar protic (SN1) |
|
|
Term
Indicate whether the following situations would increase, decrease, or not affect the rate of an SN1 reaction. Answers should follow what you learned in lab lecture.
1) Decrease temperature
2) Change the leaving group from Cl to I
3) Decrease concentration of the nucelophile
4) Change solvent from water to ethanol
5) Change the leaving group from Br to Cl
6) Increase concentration of nucleophile
7) Change solvent from acetone to ethanol
8) Increase temperature
9) Change solvent from ethanol to water |
|
Definition
1) Decrease rate
2) Increase rate
3) No effect on rate
4) Decrease rate
5) Decrease rate
6) No effect on rate
7) Increase rate
8) Increase rate
9) Increase rate |
|
|
Term
Indicate whether the following situations would increase, decrease, or not affect the rate of an SN2 reaction. Answers should follow what you learned in the lab lecture.
1) Increase temperature
2) Change the leaving group from Br to F
3) Decrease concentration of the nucleophile
4) Change solvent from ethanol to acetone
5) Decrease temperature
6) Change the leaving group from Cl to I
7) Increase concentration of nucleophile
8) Change solvent from acetone to water |
|
Definition
1) Increase rate
2) Decrease rate
3) Decrease rate
4) Increase rate
5) Decrease rate
6) Increase rate
7) Increase rate
8) Decrease rate |
|
|
Term
| Why are polar aprotic solvents preferable for the SN2 reactions? |
|
Definition
| 1) Salvation of the nucleophile cannot occur leading to a faster reaction |
|
|
Term
| Why are polar protic solvents preferable for SN1 reactions? |
|
Definition
| 1) They stabilize the transition state more than it does the reactants, lowering the activation energy; this increase the rate of the reaction |
|
|
Term
| What is the reason a false positive may occur if you use too much alkyl halide in the nucleophilic substitution reaction? |
|
Definition
| 1) Alkyl halide can act as a solvent in which the nucleophile is insoluble |
|
|
Term
| List the reason why aryl or vinyl halides do not undergo SN1 |
|
Definition
| 1) The carbocations are not stable enough |
|
|
Term
| List the reason why aryl or vinyl halides do not undergo SN2 |
|
Definition
| 1) Electrons in nearby double bonds of the aryl and vinyl halides repel the nucleophile for SN2 |
|
|
Term
|
Definition
| When a mixture is heated to the boiling point of the solvent but evaporation does not occur |
|
|
Term
| We are carrying out the esterification reaction by removing water azeotropically. Water can also be removed by using molecular sieves. Why can't calcium chloride pellets be used instead to remove water? |
|
Definition
| 1) Calcium chloride pellets and other drying agents cannot remove water at the temperature levels in which esters are made |
|
|
Term
| What two features of the azeotrope of water, 1-butanol, and butyl acetate allow for the esterification to be carried out the way it is? |
|
Definition
|
|
Term
| A solid resin is used as a catalyst for the esterification reaction. What is the resin (explain the composition)? What is the advantage of using resin for the esterification reaction? |
|
Definition
1) Resin is an orange sand-like acid catalyst which is used to speed up the reaction rate.
2) Resin functions as an effective catalyst because it can easily be filtered by vacuum or Hirsh filtration. |
|
|
Term
| If H2SO4 had been used in the esterification reaction as the acid catalyst instead of solid resin, you would have had to wash the ether layer containing the product with sodium chloride. What is the specific purpose of this wash? |
|
Definition
| 1) Sodium chloride (NaCl) forces water into the aqueous layer from the organic layer |
|
|
Term
| If you had carried out a simple distillation on the product of the synthesis of n-butylacetate from acetic acid and 1-butanol, what would you be separating the ester from? |
|
Definition
|
|
Term
| Why would it have been suitable to carry out a simple distillation on the esterification reaction mixture after azeotropic distillation to separate the product from the starting material when the boiling point difference between the product and starting materials was only nine degrees? |
|
Definition
| 1) There was not much starting material (the starting amount was very small) |
|
|
Term
| What specific aspect of the acid-catalyzed esterification reaction that you carried out does not allow for 100% product formation? (Ignore sources of error that involve product loss). |
|
Definition
| 1) The reaction is in equilibrium and you can never completely shift toward the product |
|
|
Term
| After synthesizing n-butylacetate from acetic acid and 1-butanol (esterification reaction) you take an IR spectrum of the product. What functional group peak SHOULD NOT show up if your product is absolutely pure? |
|
Definition
|
|
Term
| If H2SO4 had been used in the esterification reaction as the acid catalyst instead of the solid resin, you would have had to wash the ether layer containing the product with sodium bicarbonate. What is the specific purpose of this wash? |
|
Definition
|
|
Term
| After synthesizing n-butylacetate from acetic acid and 1-butanol (esterification reaction) you take an IR spectrum of the product. You notice a broad peak showing up at about 3200cm. List all species in the particular experiment that would cause this peak. |
|
Definition
1) 1-butanol
2) Acetic acid
3) Water |
|
|
Term
| In the esterification experiment you carried out, why did the apparatus have to be set up on an angle? |
|
Definition
| 1) In order for the aqueous layer and less dense organic layer to collect in the sidearm |
|
|
Term
| What is the role of the first 0.5 mL of water that is added in the reduction reaction? |
|
Definition
| 1) Hydrolyze sodium borohydride (NaBH4) |
|
|
Term
| What is the role of the 1 mL of hot water (after the first addition of 0.5 mL) added to the clear solution in the reduction reaction? |
|
Definition
| 1) To dilute the solution to the point of saturation |
|
|
Term
| Why is it important to keep the benzil in ethanol solution in ice when borohydride is added in the reduction reaction? |
|
Definition
| 1) To control the reaction rate |
|
|
Term
| List three reasons why sodium borohydride is a better choice for the reaction of benzil instead of lithium aluminum hydride? |
|
Definition
1) Milder
2) More selective in reducing ketones and aldehydes
3) Does not react violently when in contact with water |
|
|
Term
| Why are reductions using lithium aluminum hydride run in ether while reactions using sodium borohydride are run in ethanol or methanol? |
|
Definition
| 1) NaBH4 reduces rapidly in methanol or ethanol at 25 degrees Celsius |
|
|
Term
| List three reasons an excess of sodium borohydride is used in the reduction experiment. |
|
Definition
1) Ensure the reaction goes to completion
2) To account for decomposition
3) To account for NaBH4 to react with solvent |
|
|
Term
| Why can meso-hydrobenzoin be separated from (R,R) and (S,S) hydrobenzoin by recrystallization? |
|
Definition
| 1) Since they are diastereomers of each other |
|
|
Term
| In the reduction of benzil to hydrobenzoin you use an excess of sodium borohydride. The formation of which side product(s) (provide specific name(s)) would you minimize in the above situation? |
|
Definition
| 1) (R,R) or (S,S) hydrobenzoin and R&S benzoin |
|
|
Term
In the reduction reaction, the hot water and the 95% ethanol act as a solvent pair for the benzil. Which is the better solvent and which is the poorer one?
1) Better solvent?
2) Poorer solvent? |
|
Definition
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|
