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Distillation Technique Quiz

1) The literature reports a boiling point for cyclohexanol of 161°. In Boulder, Colorado, the atmospheric pressure is usually about 625 mm Hg. In Boulder, what is the observed boiling point of cyclohexanol?

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2) You have been given an unknown compound by your TA and told only that it is an ester. You determine the boiling point by simple distillation to be 133°. The atmospheric pressure is 625 mm. What is the corrected boiling point of the compound? For fun, look in the table of physical data at the end of the Handbook and determine which ester it might be (it smells like bananas).

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3) Which of the following compound pairs could be separated by simple distillation?

  1. acetone and aniline
  2. butyl acetate and butanol
  3. cyclohexane and cyclohexanol
  4. hexanes and toluene

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4) Refer to the figure below. If the mole fraction of B in the liquid is 0.8, what is the composition of B in the vapor above the liquid? What will be the reading on the thermometer at this point?

Distillation curve

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5) You prepare a fractionating column by filling the condenser in your lab drawer with glass beads. The glassware in the teaching labs is not entirely uniform from one student drawer to the next, and you notice that when your neighbor packs his condenser with glass beads, he is able to fit a lot fewer beads into the condenser than you are. Whose column will be more efficient as a fractionating column, and why?

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6) Why is a fractionating column packed with glass beads more efficient than a Vigreux column of the same length and same diameter?

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7) While distilling 50 mL of aniline which you prepared in the lab by a procedure involving an aqueous reaction, you record a boiling point (in Colorado) of 92°. The temperature remains at this value throughout most of the distillation. However, the distillate drips into the receiving flask as cloudy drops, and separates in the flask as two layers. Explain.

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8) Eugenol (clove oil) has a reported boiling point of 255°C at 760 mm Hg. When determining the value of a boiling point at the greatly reduced pressures used in vacuum distillations, you must use a nomography chart rather than the boiling point correction formulas. Use the nomogram given below to determine the boiling point under:

  1. water aspirator vacuum, about 25 torr
  2. mechanical pump vacuum, about 0.1 torr
Nomogram

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9) Each of the distillation set-ups pictured below has something wrong with it. Figure out what the problem is for each one.

Setup 1
Set-Up 1
Setup 2
Set-Up 2
Setup 3
Set-Up 3
Setup 4
Set-Up 4

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