Gravity Filtration

Selecting the Filter Paper

IMAGE. The filter paper should be slightly larger than the funnel.

Select a piece of filter paper that, when folded, will barely extend above the top of the funnel. In general the diameter of the unfolded filter paper circle should be about twice the diameter of the top of the funnel.

Paper is available with different separation properties. Coarse, medium, and fine grades are typically available. Coarse grades will separate relatively large particles from the liquid. Fine grades will separate all but the smallest particles from the liquid, and medium grades will perform somewhere in between. The finer the grade, the more time it will take for the filtration. Thus, you should select the coarsest grade that will completely separate the solid from the liquid (this selection comes with experience).

Note: If the filtrate contains solid after the filtration, check for leaks or channels in the filter. Barring a leak or channel, select a finer grade of paper or fritted glass for the next experiment.