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Movie Size - .5 MB Movie Duration - 16 Seconds File - CCA6/MOVIES/Labcurrent/vacfilt/01520900.MOV

Discussion

A trap is placed between the vacuum apparatus and the filtering flask to prevent contamination of the filtrate and/or prevent the filtrate from reaching the vacuum apparatus. The trap can be assembled with an Erlenmeyer flask, a three-hole rubber stopper, glass tubing, rubber vacuum tubing, and a hose clamp (or a valve).

Glass tubing is inserted into each hole on the stopper. To two of the glass tubes, 1-3 foot lengths of rubber vacuum tubing are connected. One length is connected to the receiving flask, and the other length is connected to the vacuum source. To the third glass tube, a 3-4 inch length of rubber vacuum tubing is connected and the tubing clamp is loosely attached. The assembled stopper is then placed in the opening of the flask.

When working with an aspirator, the trap is configured as shown in the figure above so as to protect the Buchner Flask from "suck back" that might damage a filtrate the student is collecting. When doing vacuum filtration with a vacuum pump, however, we reverse the configuration as shown in the figure below, preferring to protect the vacuum pipes and pump from having water sucked into them at the possible expense of ruining a student's filtrate. Given that there is no aspirator that could inject water into the system in a "suck back" situation, there is little risk that this choice of configuration will cause damage to a student's filtrate.

Clamp the side-arm receiving flask to a ring stand. Then, connect the side-arm receiving flask to the trap and place the Buchner funnel or glass crucible in the mouth of the receiving flask.

Narrative

Firmly clamp the filter flask and attach a hose from the trap to the arm of the flask. Firmly attach the funnel to the mouth of the flask.