In this worksheet, we will practice describing the purification of compounds by gravity and vacuum filtrations, assessing hazards and common errors.
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.
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.
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
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.
Which of the following physical processes is not likely to be observed in the filtrate during a vacuum filtration?
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
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.
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.
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.