Worksheet: Filtration

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?

  1. Turning off the aspirator
  2. Disconnecting the aspirator from the flask
  3. 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.

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