[Music] hi and welcome back to freesis lessons. co.uk by the end of this video you should be able to explain why ionic compounds can conduct electricity when molten or dissolved in water you should then be able to describe the reactions taking place at the positive and negative electrodes during electrolysis and finally you should be able to describe the reactions as either reduction or oxidation and that's for higher tier students only now electrolysis can seem like quite a tricky topic so I'm going to split this over several videos I should point out it's not as tricky as it first appears in this video we'll explore the general ideas behind electrolysis and in later videos we're going to look at some specific examples which you need to learn we're going to start by recapping ionic compounds this is the ionic compound lead bromide this is formed when lead react with bromine when lead bromide forms a lead atom loses two electrons like this forming the lead ion pb2+ these two electrons then pass on to two bromine atoms forming two bromide ions BR minus like this now we formed our ionic compound pbbr2 so as you can see lead bromide contains two different ions the lead ion pb2+ and the bromide ion B minus so what happens when we carry out electrolysis on ionic compounds such as lead bromide let's start by looking at some key facts about electrolysis here's the first key fact solid ionic compounds cannot conduct electricity and that's because the ions are locked in place they're not free to move I'm showing you the structure of a solid ionic compound here this is lead broide which we saw before but the idea applies to all ionic compounds as you can see the ions are locked in a regular pattern they're held in place by strong electrostatic forces of attraction so the ions are not free to move however when an ionic compound is melted or dissolved in water the forces of attraction are broken and the ions are free to move because the ions can now move these liquids and solutions can now conduct electricity and scientists call these liquids or Solutions electrolytes so we're going to look now at what happens when we carry out electrolysis on a molten ionic compound such as lead bromide remember that the word molon means melted so lead bromide contains two ions the positive lead ion pb2+ and the negative bromide ion BR minus in electrolysis we've got two electrodes these are made of a conducting material such as graphite or a metal the negative electrode is called the cathode that's attached to the negative terminal of a power Park think of the cathode as being covered with electrons which are coming from the power Park the positive electrode is called the anode that's connected to the positive terminal of the power PK think of the anode as having a lack of electrons here's our molten lead bromide we can see the positive lead ions here and we can see the negative bromide ions here the positive lead ions are attracted to the negative electrode and that's because opposite charges attract the lead ions now gain two electrons to form lead atoms because the lead ions are gaining electrons that's an example of a reduction reaction the negative bromide ions are attracted to the positive electrode here they lose one electron to form bromine atoms because the bromide ions are losing an electron that's an example of an oxidation reaction now I should point out that bromine atoms pair to form a bromine molecule so we usually show the reaction like this in the next video we're going to look at how we can use electrolysis to extract reactive metals such as aluminium remember you'll find plenty of questions on electrolysis in my vision workbook and you can get that by clicking on the link above okay so hopefully now you should be able to explain why ionic compounds can conduct electricity when molten or dissolved in water you should then be able to describe the reactions taking place at the positive and negative electrodes during electrolysis and finally you should be able to describe the reactions as either reduction or oxidation and that's for higher tier students only [Music]