Lesson Worksheet: Filtration Chemistry
In this worksheet, we will practice describing the purification of compounds by gravity and vacuum filtrations, assessing hazards and common errors.
Q1:
What is the main disadvantage of using a larger funnel for a gravity or a vacuum filtration?
- ASolvent flows through the funnel more slowly, increasing the time needed to complete the filtration.
- BMore product adheres to the funnel, making it difficult to retrieve.
- CThe funnel is more difficult to clean after the filtration is complete.
- DMore solvent is needed to wash the product effectively.
- EThe funnel is more difficult to handle, increasing the chance of breakages when the apparatus is assembled.
Q2:
What is the main disadvantage of using a smaller funnel for a gravity or a vacuum filtration?
- AThe solid product forms a thicker and more compact layer, making it more difficult to retrieve.
- BThe funnel is more difficult to handle, increasing the chance of breakages when the apparatus is assembled.
- CSolvent flows through the funnel more slowly, increasing the time needed to complete the filtration.
- DThe funnel is more difficult to clean after the filtration is complete.
- EFor a given volume of washing solvent, the final purity of the product is reduced.
Q3:
Which of the following pieces of apparatus is not typically used in vacuum filtrations?
- AA condenser
- BA Büchner funnel
- CA clamp
- DAn aspirator
- EA rubber tubing
Q4:
When collecting a precipitate under suction, which of the following steps is not required?
- AThe Büchner flask is attached to the aspirator or vacuum line.
- BA Büchner or sintered funnel is attached with a ground glass joint or rubber seal.
- CVacuum is applied using an aspirator or vacuum pump.
- DThe aspirator or vacuum pump is turned off before removing the tubing from the flask.
- EA clamp is used to secure the Büchner flask.
Q5:
Which of the following physical processes is not likely to be observed in the filtrate during a vacuum filtration?
- AFoaming
- BBoiling
- CMelting
- DPrecipitation
- EFreezing
Q6:
When a Büchner filtration is complete, in which order should the following actions be performed?
- Turning off the aspirator
- Disconnecting the aspirator from the flask
- Collecting the filtered solid
- A2, 1, 3
- B2, 3, 1
- C3, 1, 2
- D1, 2, 3
- E3, 2, 1
Q7:
After a Büchner filtration, solid is observed in the collected filtrate. Which of the following is the least likely explanation?
- AThe Büchner funnel or flask were not properly washed before use.
- BThe solvent added to wash the filtered solid caused further precipitation in the filtrate.
- CThe filter paper was not properly sealed to the Büchner funnel.
- DPrecipitation was caused by cooling of the filtrate under vacuum.
- EThe solid passed through the filter paper.
Q8:
In gravity filtration, filter paper is often folded into a fluted shape, as shown. Why is the efficiency of filtration increased if fluted filter paper is used instead of a simple paper cone?
- AFor a given funnel, fluted filter paper can accommodate a larger solvent volume than a filter paper cone.
- BFor a given funnel, fluted filter paper has a larger surface area than a filter paper cone.
- CWhen the filtration is complete, it is easier to retrieve a solid product from fluted filter paper.
- DThe folds in fluted filter paper channel solvent onto the solid contents, reducing the volume of solvent needed.
- EFluted filter paper provides a better seal to a glass funnel than a filter paper cone.
Q9:
A student performs a gravity filtration using the apparatus shown. In what way has the apparatus been incorrectly assembled?
- AThe Erlenmeyer flask should be heated.
- BThe wash solvent should be added using a volumetric pipet.
- CA sintered funnel has not been used.
- DA stir bar should be added to the filtrate.
- EThe flask should be clamped in a lower position.
Q10:
A student performs a vacuum filtration using a sintered glass funnel and a water aspirator, as shown.
In what way has the apparatus been incorrectly assembled?
- AThe neck of the flask should be clamped, instead of the funnel.
- BThe flask should be connected to the aspirator, instead of the funnel.
- CA filter paper should be placed into the sintered funnel.
- DThe flask should be connected to a gas supply.
- EThe neck of the flask should be clamped, in addition to the funnel.
Why is it potentially hazardous to turn off the water aspirator before disconnecting it from the flask?
- AThe filtrate could be sucked out of the flask.
- BThe tube may become difficult to remove, increasing the risk of breakage.
- CThe tube could be pulled violently from the flask.
- DAir could be forced through the funnel, expelling the collected solid.
- EWater could be sucked back into the flask.
Which of the following is not an advantage of the sintered funnel, as compared to a ceramic funnel with a paper filter?
- AA glass sinter provides a tighter and more consistent seal to the funnel.
- BA glass sinter is more suitable for filtering very fine precipitates.
- CA glass sinter can be cleaned more easily.
- DA glass sinter is less reactive to acidic solutions.
- EA glass sinter is less reactive to basic solutions.
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