Lesson Worksheet: Distillation Chemistry • 10th Grade
In this worksheet, we will practice describing the purification of solvents and other liquids by distillation, assessing hazards and common errors.
Q1:
What is the main reason for adding a stir bar to the pot still in distillation?
- AStirring the liquid reduces the risk of bumping.
- BStirring the liquid prevents phase separation as the temperature increases.
- CStirring the liquid ensures the vapor composition is uniform.
- DStirring the liquid increases the rate of boiling, making the distillation more efficient.
- EStirring the liquid allows it to be heated more uniformly.
Q2:
How could elastic bands be used in a vacuum distillation?
- ATo improve the vacuum seal by applying tension to the condenser joints
- BTo improve the condensation rate by insulating the condenser joints
- CTo secure the thermometer in the correct position near the opening of the condenser
- DTo prevent breakage by securing the apparatus in an upright position
- ETo prevent water leakage by securing the condenser tubes in the correct positions
Q3:
When performing a vacuum distillation, why is it often advantageous to use a pig adapter?
- AMultiple fractions can be collected without releasing the vacuum.
- BThe distillate can be protected from contamination if bumping takes place.
- CSamples of the distillate can be collected without releasing the vacuum.
- DMultiple fractions can be collected and stored at different vacuum pressures.
- EA larger volume of distillate can be collected.
Q4:
Which of the following precautions is most important for ensuring that the apparatus for a vacuum distillation is well sealed?
- AThe ground glass joints are secured with Keck clips.
- BThe condenser is maintained at a low temperature.
- CThe receiving flask is supported by a jack.
- DThe ground glass joints are greased.
- EElastic bands are stretched between the still head and condenser.
Q5:
Which of the following pieces of apparatus is not typically used in distillations?
- AHot plate
- BKeck clip
- CFunnel
- DCondenser
- EThermometer
Q6:
Which of the following pieces of apparatus is not used in distillations?
- A
- B
- C
- D
- E
Q7:
A student sets up a vacuum distillation using the glassware shown, in addition to other apparatus. Some connectors and other parts of the glassware are labeled.
To which position should the vacuum pump be connected?
Which positions should be supported by a clamp?
- A6 and 10
- B4 and 6
- C4 and 5
- D3 and 10
- E3 and 5
To which position should the pig adapter be attached?
To which female connectors would the attachment of Keck clips be potentially hazardous?
- A4 and 5
- B6 only
- C5 only
- D4 and 9
- E6 and 9
Q8:
A student sets up a distillation as shown to extract fractions from a mixture of biological oils.
In what way has the apparatus been incorrectly assembled?
- AThe sample material is suspended in a solvent.
- BThe apparatus is not connected to a vacuum line.
- CThe apparatus is not connected to a nitrogen supply.
- DThe flask containing the water is not directly heated.
- EThe flask containing the sample material is not directly heated.
What is the main purpose of the flask containing water?
- ATo generate steam for indirect heating and volatilization of the oil mixture
- BTo dissolve compounds evaporating from the oil mixture
- CTo denature enzymes in the oil mixture, which would otherwise degrade the extracted compounds
- DTo provide a humid atmosphere around the oil mixture, increasing the rate of heat conduction
- ETo extract water-soluble compounds from the oil mixture
Why is this procedure used in preference to a simple distillation method?
- AWater-soluble fractions are distilled selectively.
- BOverheating of the distillate is avoided.
- CExposure to water lowers the boiling point of the distillate, so a higher distillation rate can be achieved.
- DHeating with steam is more energy-efficient, so a higher distillation rate can be achieved.
- EWater-immiscible fractions are distilled selectively.
What is the main disadvantage of this procedure, as compared to a simple distillation method?
- AOnly water-soluble compounds can be distilled.
- BWater is introduced into the distillate and must be removed.
- CWater reacts with the distillate, lowering the maximum yield.
- DGreater energy and equipment requirements lead to higher costs.
- EThe use of water lowers the maximum achievable distillation rate.
Q9:
A student performs a distillation using the apparatus shown.
In what way has the apparatus been incorrectly assembled?
- AThe receiving flask is not connected to the receiver adapter via a ground-glass joint.
- BThe thermometer is positioned too high.
- CThe crude liquid should be heated in a round-bottom flask.
- DThe water is flowing through the condenser in the wrong direction.
- EThe condenser should not be supported by a clamp.
What name is given to the small round objects added to the crude liquid to prevent flash boiling?
- AStir bar
- BAnti-bumping granules
- CCatalyst
- DDesiccating agent
- EBoiling stick
A student replaces the receiver adapter with the version shown below, firmly attaching it to the receiving flask. Why is this change potentially hazardous?
- AThere is no route for dissolved gases to escape from the distillate.
- BThere is no route for pressure to be released from the system.
- CThe distillate may be sucked back into the condenser.
- DIt is more difficult to remove the receiving flask from the adapter.
- EFirmly connecting the condenser to two flasks increases the risk of breakage.
What is the main function of the thermometer in this procedure?
- ATo indicate when distillation of each fraction is complete.
- BTo allow the water flow in the condenser to be set correctly.
- CTo allow the temperature of the heating mantle to be set correctly.
- DTo indicate the identity of each collected fraction.
- ETo indicate the purity of each collected fraction.
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