[Music] I'm welcome back to three sighs lessons co uk by the end of this video you should be able to describe how we can use melting and boiling point data to determine if a substance is pure you should then be able to describe what's meant by a formulation now in chemistry a pure substance can be a single element so for example I'm showing you here Oh Lord made out of pure silicon a pure substance can also be a single compound so this shows a sample of pure sodium chloride so the key point is that a pure substance is not mixed with any other substance now though a lot of different ways to determine if a substance is pure but one of the simplest ways is to measure its mountain point and boiling point a pure substance melts at a specific fixed temperature and a pure substance also has a specific fixed boiling point now in pure substances melt and boil over a range of temperatures so if we take a substance and heat it we can measure the mountain point and the boiling point and these will tell us if the substance is pure I'm showing you here the results of that experiment using pure water so we're starting with ice under gradually increasing the temperature at a certain point the temperature stops rising this is the melting point and we can see that here as you can see the melting point in this case is fixed at a zero degrees Celsius once the water's melted the temperature increases again and again at a certain point the temperature stops rising this is the boiling point as you can see the boiling point in this case is fixed at 100 degrees Celsius so because both the mounting on the boiling point about specific fixed temperatures we know that this water's pure we get a similar shade graph for any pure substance although the melting and boiling points would not be the same as water I'm sure here the same graph but this time for a mixture of water and an impurity as you can see in this case the water Matt's unboiled over a range of temperatures this tells us that the waters not pure and again we get a similar shape graph for any impure substance now as we've said a pure substance consists of only a single element or a single compound however scientists often produce mixtures a formulation is a complex mixture that's been designed as a useful product in a formulation the quantity of each component is carefully measured so that the product has the properties that we need there are many examples of formulations and I'm showing you some of these here remember you'll find plenty of questions on pure and impure substances and on formulations in my revision workbook and you can get that by clicking on the link above [Music]