Q: When is gravity filtration used?

A: Normally when there are small amounts of solid impurities to be removed from a solution (the filtrate contains the desired material). Gravity filtration may be performed with hot solvent (in contrast with vacuum filtration).

Q: Why fold ("flute") the filter paper?

A: To give the most surface area, and to keep the paper from laying against the surface of the wide stem funnel.

Q: Why use a wide stem funnel?

A: When performing a hot filtration solute will sometimes begin to crystallize, and a narrow stem would become plugged.

Q: Should washing steps be included?

A: Yes, generally wash with a couple of small portions of the same solvent you are using - use hot solvent if it is a hot filtration. This rinses residual solute from the filter paper.

©2001,2002 Daniel A. Straus