(P) More Separation Techniques

• Chemists use physical separation techniques to separate solids from liquids
• Filtration separates insoluble solids from liquids
• Filtration can be used in purification - solid impurities can be separated from the mixture
• In filtration, filter paper is folded into a cone shape and the solid is left in the filter paper
• Evaporation and crystallisation separate soluble solids from solutions
• Evaporating salt from a solution - 1. Pour the solution into an evaporating dish
• Evaporating salt from a solution -2. Slowly heat the solution. The solvent will evaporate and the solution will get more concentrated. Eventually crystals wil start to form
• Evaporating salt from a solution - 3. 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 when it's heated. Otherwise, you'll have to use crystallisation
• Crystallisation (salt in a solution) - 1. Pour the solution into an evaporating dish and gently heat the solution. Some of the solvent will evaporate and the solution will get more concentrated
• Crystallisation (salt in a solution) - 2. 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 to cool
• Crystallisation (salt in a solution) - 3. The salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution
• Crystallisation (salt in a solution) - 4. Filter the crystals out of the solution, and leave them in a warm place to dry.
• You can use a drying oven or a desiccator to dry salt crystals
• Apart from a bunsen burner, you can also use a water bath or an electric heater in the process of evaporation
• Crystallisation is also useful if you want to make big salt crystals, not just for separation
• Filtration and crystallisation can be used to separate rock salt
• Rock 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
• Separating rock salt - 1. Grind the mixture to make sure the salt crystals are small, so will dissolve easily
• Separating rock salt - 2. Put the mixture in water and stir. The salt will dissolve, but the sand won't (you can also heat the mixture to help dissolve the salt)
• Separating rock salt - 3. 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
• Separating rock salt - 4. Evaporate the water from the salt so that it forms dry crystals (you could use crystallisation here if you wanted big crystals)