[Music] hi and welcome back to free science lessons. co.uk by the end of this video you should be able to describe how the hydrocarbons and crude oil can be separated by fractional distillation you should then be able to State the functions of the important fractions over the last couple of videos we've seen that crude oil is a mixture of molecules called hydrocarbons each hydrocarbon has a different boiling point longer chain hydrocarbons have a higher boiling point than shorter chains now in order for the hydrocarbons in crude oil to be useful we've got to separate them and to do that we use a technique called fractional distillation in fractional distillation crude oil is separated into fractions and fractions contain hydrocarbons with a similar number of carbon atoms now it's really important that you learn the stages of fractional distillation this often comes up with an exam question fractional distillation takes place in very large columns such as these ones which we find in oil refineries I'm showing you a drawing of this here firstly the crude oil is heated to a very high temperature this causes the crude oil to boil in other words all of the hydrocarbons evaporate and turn to a gas the crude oil Vapor has now fed into the fractional distillation column the column's hotter at the bottom and cooler at the top the hydrocarbon Vapors now rise up the column hydrocarbons condense when they reach their boiling point in other words they turn back to a liquid and the liquid fractions are then removed the remaining hydrocarbons continue moving up the column these now condense when they reach their boiling points now there are a couple of further points that you need to learn very long chain hydrocarbons have got very high boiling points these hydrocarbons are removed from the bottom of the column very short chain hydrocarbons have got very low boiling point and these do not condense they're removed from the top of the column as gases now as we said fractional distillation produces fractions these contain hydrocarbons with a similar number of carbon atoms some fractions are used as fuels and I'm showing you some examples here petrol and Diesel are used to fuel cars kerosene's used as jet fuel heavy fuel oil is used to power shift and liquefied petroleum gas is used in camping stoves and we looked at how hydrocarbons are used as fuels in the last video now some fractions are used as feed stock for the petrochemical industry and the word feed stock means a chemical that's used to make other chemicals and I'm showing you some of these here so feed stock fractions are used to make solvents lubricants detergents and polymers remember you'll find plenty of questions on fractional distillation in my vision workbook and you can get that by clicking on the link above [Music]