Lab final

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Lab final
2014-12-08 14:58:00
lab final
O Chem
LAb final on 12/8
Show Answers:

  1. Criteria and NOT criteria for re-crystallization compound
    • 1. inexpensive and safe to use
    • 2. The compound should be insoluble in cold solvent.
    • The solvent should react with the compound.
    • 3. The compound should be soluble in hot solvent.
    • NOT criteria:
    • 1.The solvent should react with the compound.
  2. Purpose of recrystallization of compound
    to purify compound
  3. True about melting compound:
    The melting point of an impure compound is lower than that of a pure compound
  4. A sample begins to melt at 76 °C and is completely melted at 80 °C.  The melting point of this sample is characterized by:
    The range of the initial temperature and the final temperature (e.g., 76-80 °C).
  5. When a water-jacketed condensor is used in a distillation, where should  water enter and exit the condenser for most efficient cooling of hot vapor?
    Cooling water should enter at the bottom of the condenser and exit at the top of the condenser.
  6. Heat source for distillation:
    a heating mantle and regulator
  7. describes the storage of the thermometers and the packed fractionaing columns used in this experiment?
    They should remain available in a common location  for use by other lab sections.  (For example, give them to your TA or place them in the reagent hood or a location designated by your TA.
  8. A simple distillation apparatus (like the one shown in your experiment procedure) is used for the separation of the components of a binary mixture.Which binary mixture listed below is most likely to give the best separation of the two components using simple distillation?
    Yes, you are correct. When the boiling points are very far apart, it is easy to separate them using a simple distillation apparatus.
  9. Used in simple distillation apparatus?
    • 1. receiving flask
    • 2. water jacketed condenser
    • 3. thermometer
  10. aq. NAOH, ether, benzoic acid (PhCOOH) , nonpolar neutral compound, into 2 layers?
    • Top layer: nonpolar comp., ether, 
    • Bottom: NAOH, water sodium benzoate( PhCOO.Na+) , dissolved, not reacted
  11. In this experiment, how will the pure organic acid (Ph-COOH) be generated froman aqueous solution (pH = 10) of sodium benzoate (Ph-COONa+)?
    treatment of the aqueous solution with acid followed by filtration
  12. In this experiment, how will the pure neutral compound be recovered from its solution?
    isolation of the ether solution, treatment with a drying agent, removal of the drying agent, and then rotary evaporation.
  13. Which method can be used in the lab to quickly differentiate and identify the organic layer in a separatory funnel?
    Add a small amount of water to the mixture to see which layer increases in volume.
  14. Which one of the following statements concerning TLC in this experiment is true?
    The organic acid (Ph-COOH) is a polar compound and it will have a low Rf value.
  15. Which of the following halogens is most reactive under radical reaction of alkanes?
    Yes, Correct. The reactivity order is F2 > Cl2 > Br2 > I2
  16. How many mono-chlorinated organic product(s) will form in the reaction of 3-ethyl-2-methylpentane with Br2 in presence of light?
  17. Consider each pair of compounds shown below. Which pair of compounds can be easily distinguished using infraredspectroscopy?
  18. Which statement(s) related to this experiment is(are) true? (Select ALL that apply)
    • a. All chemical wastes from this experiment should go in the Halogenated Organic Waste bottle.
    • b. Even though the bromine solution in this experiment is very dilute, you must still be cautious since bromine itself iscorrosive.
    • c. In this experiment, we will be heating the reaction mixture with a flame to accelerate the reaction.
    • d. Methylene chloride (also known as dichloromethane) is a halogenated solvent.e. In this experiment one should not look directly into the UV light being emitted by the handheld UV lamps
  19. What important factor is used to our advantage in the separation of the reactant and product in today’s experiment?
    Alkenes boil at lower temperature than their corresponding alcohols.
  20. In this experiment, a portion of the product with be treated with a few drops of a reddish-brown solution of bromine in dichloromethane.  Which of the following choices best describes the evidence that will indicate that bromine has been consumed by the alkene?
    reddish brown color disappears immediately , becoming colorless solution
  21. In this experiment, why is the distillate washed with solution of sodium carbonate?
    to neutralize residual acid.
  22. this type of reaction is....
    addition rxn
  23. Which of the following statements is not true?
    • a. Most or all of the product in this experiment should be dissolved (in solution) when the mixture is hot (at 50 °).
    • b. The product should crystallize from solution as the mixture cools in an ice-water bath.
    • c. The product should be colorless to faint yellow.
    • d. An intense blue product solution indicates that the bromination of trans-cinnamic acid complete. ( all true except d)
  24. which is true?
    • a. Dilute acetic acid will be used in this experiment. It does not pose a safety hazard.
    • b. Dilute bromine solution will be used in this experiment. It does not pose a safety hazard if it is spilled on your skin.
    • c. Used glass pipettes may be discarded in a common trash container near a sink.
    • d. In this experiment, you should avoid contact with bromine and acetic acid. Both are are corrosivel. Skin contactshould be avoided.
  25. It is likely that compounds that are diastereomers should have
    • a. different melting points.
    • b. different boiling points.
    • c. diffferences in solubility in a given solvent
    • (ALL)
  26. Consider the reaction of (S)-pentan-2-ol (shown below).  This reaction follows a SN2 reaction mechanism.  Choose the correct structure of the product (with correct stereochemistry).
    A ( inversion always present with sn2)
  27. The main reaction in this experiment is shown below.  During the work-up of the reaction mixture, what is the main purpose of carefully and slowly adding aqueous sodium bicarbonate solution to the crude product rather than adding all of the solution at once?
    Careful and slow addition will minimize any bubbling and frothing that might result.
  28. How does the use of concentrated sulfuric acid help promote the reaction of 1-butanol with HBr?
    To make hydroxyl group a better leaving group
  29. A mixture of 1-pentanol, concentrated hydrobromic acid, and sulfuric acid produces 1-bromopentane.  This reaction follows a SN2 reaction mechanism.  Consider the effect of running the same reaction again using twice as much solvent.  In other words, the new concentration of 1-pentanol and hydrobromic acid would each be nearly halved.  How would the two reaction rates compare?
    The reaction rate for the dilute mixture would be one-fourth of that corresponding to the original mixture.
  30. Which product(s) should be formed in the reaction shown below?
    A and B (sn1 reaction)
  31. If 5.3 g of tert-pentyl chloride (F.W. = 106 g/mol) is isolated from the reaction of excess of concentrated HCl with 11 mL of tert-pentyl alcohol (density = 0.8 g/mL, F.W.= 88 g/mol), what is the percent yield?
  32. If excess chloride ions (for example, in the form of NaCl) are added to the reaction mixture for the equation shown below,(along with tert-pentyl alcohol and concentrated hydrochloric acid), what will be the result?
    There will be no noticeable change in the rate compared to the reaction without the presence of sodium chloride
  33. Which functional group is associated with the absorptions indicated with an arrow in the infrared spectrum shownbelow?
  34. mass spectroscopy for which one in C8H8?
    m/z = 120
  35. What information can be gained from the integration (or intensity) of 1H NMR signals?
    The relative number of equivalent protons for a given signal.
  36. Consider the 1H NMR spectrum that corresponds to the compound shown.Which of the following is the correct assignment for the signals?
    Consider the 1H NMR spectrum that corresponds to the compound shown.Which of the following is the correct assignment for the signals?
  37. Cyclopentadiene has a very short shelf life because
    it quickly reacts with itself at room temperature.
  38. The classic Diels-Alder reaction is best facilitated by
    an electron-withdrawing group on the dieneophile and an electron-donating group on the diene
  39. dienophile a
  40. what was purpose of treating 4-methykcyclohexanol with a mixture of phosphoric acid and sulfuric acid? (What leaving group was initially formed?)
    • Purpose:
    • make H+ to protonate OH-, which will be the leaving group.
    • 2. Acids also used bc they're conjugate bases are weak , do not lead to additional rxns
  41. Why distillate washed with aqueous sodium carbonate soln:
    removes any remaining acid left from the reaction so that the acids can be disposed of properly
  42. why rxn mixture bubbled and fizzed upon addition of aqueous sodium carbonate?
    Reaction of sodium carbonate with phosphoric/sulfuric acid released CO2
  43. if final "product" was mixture of alkene (75%) and original alchohol (25%) , would you be able to verify this by using the chemical tests of unsaturation in this experiment? Explain
    Yes, bc the amount of color is directly correlated with quantity of compounds.
  44. if final product was a mixture of of the alkene (75%) and original alcohol , could this be verified by Infrared spectroscopy? Explain.
    No because since the spectroscopy shows all stretches regardless of quantity, as long as there is some alkene present, it's particular transmittance will be shown regardless of quantity
  45. you allow solution to cool in an ice bath, and no crystals form. at this point what can be done to facilitate crystallization?
    add more solute and reheat to repeat procedure
  46. you allow solution to cool in icebath and no crystals form. what mistake may have caused the crystals not to form?
    there may have been too much solvent to allow the solute to recrystallize
  47. why is hot solution sometimes filtered before it is allowed to cool?
    if the hot solvent does not dissolve the impurities, then the hot mixture must be filtered
  48. max percent recovery if initially 4.0 g of acetanilide , and in cold water solubility is .53 g?
    |.53-4|/4 *100 = 87.7%