Filtration separates insoluble solids from liquids

• Filtration can be used if your product is an insoluble solid that needs to be seperated from a liquid reaction mixture

• It can be used in purification as well. For example, solid impurities in the reaction mixture can be separated out using filtration

  • Insoluble means the solid can’t be dissolved in the liquid

Two ways to separate soluble solids from solutions

• If a solid can be dissolved it’s described as being soluble. There are two methods you can use to separate a soluble salt from a solution-evaporation and crystallisation

• Evaporation

  • Pour the solution into an evaporating dish

  • Slowly heat the solution. The solvent will evaport and the solution will get more concentrated. Eventually, crystals will start to form

  • Keep heating the evaporating dish until all you have left are dry crystals

• Evaporation is a really quick way of separating a soluble salt from a solution, but you can only use it if the salt doesn’t decompose(break down) when its heated. Otherwise, you’ll have to use crystallisation

• Crystallisation

  • Pour the solution into an evaporating dish and gently hear the solution. Some of the solvent will evaport and the solution will get more concentrated

  • Once some of the solvent has evaporated, or when you see crystals start to form(the point of crystallisation), remove the dish from the heat and leave the solution to cool

  • The salt should start to form crystals as it become insoluble in the cold, highly concentrated solution

  • Filter the crystals out of the solution, and leave them in a warm place to dry. You could also use a drying oven or a desiccator

Filtration and crystallisation can be used to separate rock salt

• Roc salt is simply a mixture of salt and sand(they spread it on the roads in winter).

• Salt and sand are both compounds-but salt dissolves in water and sand doesn’t. This vital difference in their physical properties gives a great way to separate them. Here’s what to do…

  • Grind the mixture to make sure the salt crystals are small, so will dissolve easily

  • Put the mixture in water and stir. The salt will dissolve, but the sand won’t.

    • You can heat the mixture to help dissolve the salt

  • Filter the mixture. The grains of sand won’t fit through the tiny holes in the filter paper, so they collect on the paper instead. The salt passes through the filter paper as it’s part of the solution

  • Evaporate the water from the salt so that it forms dry crystals