Vacuum Filtration

Washing the solid

Washing the solid is important whether the solid or the filtrate will be collected.

• If the solid is to be collected, washing will remove any soluble impurities.
• If the filtrate is to be collected, washing will ensure that all of the solute (a compound that you want which is in solution in the filtrate) is removed from the solid and collected in the filtrate.

To wash the solid, add a small amount of solvent to the funnel with the vacuum off. Stir the solid to disperse it into the solvent. Be careful not to dislodge or tear the filter paper as you stir the sample, or some of your solid sample is likely to go through the funnel into the filtrate.

After the solid has been suspended in the solvent, turn the vacuum on again and allow the liquid to pass through the funnel. Repeat this washing process until the all soluble species are removed. If the filtrate is to be collected, the volume of washes should be minimized so that it does not take a lot of effort to remove the solvent.