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 separation 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 chemicals 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. And scientists call this 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.