[Music] hi and welcome back to free science lessons by the end of this video you should be able to describe physical separation techniques now there are several different physical saturation techniques but in this video we're going to focus on filtration and crystallization the first idea you need to understand is that physical separation techniques can only be used to separate mixtures they cannot be used to separate the elements in a compound in a later topic we look at how we separate the elements in compounds for example by chemical reactions such as reduction or by electrolysis in this video we're focusing on physical separation techniques and how they're used to separate mixtures we're going to start by looking at one of the simplest separation techniques which is filtration filtration is used to separate an insoluble solid from a liquid and the word insoluble means that the solid will not dissolve in the liquid I'm showing you here the chemical silver chloride and water you'll notice that I've also included lowercase letters next to the formula of each chemical these are called state symbols state symbols tell us the physical state of a chemical for example whether it's a solid a liquid a gas or dissolved in water the S tells us that silver chloride is a solid and the L tells us that water is a liquid now silver chloride is insoluble in water in other words silver chloride will not dissolve in water and in the AQA exam you'll be given any solubilities that you need to know so I have a solid material suspended in a liquid and I'm showing you that here now in reality you would not be able to see individual particles of silver chloride but it does illustrate the idea so because this silver chloride is insoluble in water we can use filtration to separate these two substances to do this we use a filter funnel and a filter paper like this we start by pouring our mixture into the filter paper the liquid in this case the water passes through the tiny pores in the filter paper inside is coreless liquid the filtrate however the solid material in this case the silver chloride cannot pass through the filter paper so it's trapped at the end we have our liquid separated from our solid so as we've seen filtration separates an insoluble solid from a liquid filtration is a really useful physical separation technique and it's used a lot in chemistry another important physical separation technique is crystallization crystallization is used to separate a soluble solid from a liquid in this example we have sodium chloride and water sodium chloride is soluble in water so when we mix sodium chloride with water the sodium chloride dissolves and we form sodium chloride solution the state symbol AQ means that the sodium chloride is dissolved in water and scientists call this an aqueous solution imagine that we want to separate the sodium chloride from the water so here's our sodium chloride solution now if we leave this solution for a few days then the water will evaporate and this will leave behind crystals of solid sodium chloride like this you can see that I've changed the state symbol for the sodium chloride from AQ to s that's because the sodium chloride is no longer dissolved in water it's now a solid we can make crystallization happen faster by gently heating our solution to evaporate the water however we do need to be careful certain chemicals will break down if we heat them so sometimes it's better to allow the water to evaporate on its own you'll find plenty of questions on this topic in my vision workbook which you can get by clicking on the link above [Music] good foreign