Filtration We know that some solids are soluble in water and some are not. If the solids are insoluble (not soluble) in water we can separate them from the water by filtration. To filter a mixture we use filter paper. Filter paper has
tiny holes in it that only let some materials pass through. The materials that cannot pass through are trapped on the filter paper. We use this method to separate insoluble solids from liquids. The liquid passes through and is called the filtrate. The part that remains on the filter paper is called the residue.
Activity Separating sand and water using filtration
Apparatus Beaker, funnel, filter paper, conical flask, stirring rod, sand and water
Fig. 6
Method 1. Place a small amount of sand in a beaker of water and stir it well.
2. Fold the filter paper in half and then in half again as shown in Fig. 6.
3. Hold it by the pointed corner. Pull out one of the outside flaps so that it forms a cone with three flaps on one side and one flap on the other.
Filter paper (folded in half) Retort stand Filter paper (folded again)
Beaker Sand
Filter paper Funnel
Conical flask Liquid
Filter paper
Residue
Filtrate
Fig. 5 Separating an insoluble solid from a liquid.
Fig. 7 Separating sand and water by filtration.
4. Put the cone-shaped filter paper in the funnel. 5. Give the sand and water mixture a final stir and then pour it quickly into the funnel. Be careful not to overfill the funnel. 6. Wait for the water to pass through and see what happens.
Evaporation What would happen if a mixture of salt and water was passed through filter paper? Because salt is soluble in water it will pass through the filter paper with the water. Evaporation is used to separate a soluble solid, like salt, from a solvent. The solution is heated up until the liquid particles get enough energy to form a gas. The gas particles spread out into the room leaving the solid particles behind on the clock glass.
