[Music] hi and welcome back to free science lessons. co.uk by the end of this video you should be able to describe why electrolysis is used to extract some metals you should then be able to describe how aluminium is extracted by electrolysis finally if you're a higher tier student you should be able to write half equations for the reactions at the cathode and the anode that can seem a little bit tricky but the best approach is to learn them in a previous video we saw that we can list the elements in order of their reactivity and
I'm shown you that here Metals which are less reactive than carbon can be extracted by reduction with carbon however Metals which are more reactive than carbon are extracted using electrolysis so in this video we're looking at how electrolysis is used to extract metals from compounds and a good example as aluminium aluminium has got a very low density and it's used to make objects from drink C to aircraft we've got to extract aluminium from the compound aluminium oxide using electrolysis so let's take a look at that now I'm showing you aluminium oxide here aluminium oxide contains
the aluminium ion al3+ and the oxide ion O2 minus aluminium oxide has a very high melting point it's around 2000° C in the first stage aluminium oxide is mixed with the compound cryolite now that lowers the Mountain point this reduces the amount of energy needed and it saves money now we apply an electric current to the molten aluminium oxide I'm showing you the setup here the cathode and the anode are made of graphite and that's a form of carbon graphite is a Very Good Conduct of electricity and it's got a very high melting point so
we can use it at high temperatures without melting here are the aluminium ions al3+ and the oxide ions O2 minus these ions are free to move because this is molten aluminium oxide and remember that the word molten means melted the aluminium ions al3+ are attracted to the cathode which is the negative electrode here each ion gains three electrons and forms an aluminium atom now if you're doing the higher TI then you need to memorize the half equation which I'm showing you here that's an example of a reduction reaction because the aluminium ion is gaining electrons
and again you need to memorize that the oxide ions O2 minor are attracted to the positive terminal in other words the anode each oxide ion loses two electrons to form an oxygen atom again if you're a higher student you need to memorize the half equation which I'm showing you here because the oxide ions are losing electrons that's an example of an oxidation reaction now there are some points about the reaction of the anode that we need to look at we've already seen the half equation for the anode remember that oxide ions are losing two electrons
to form oxygen atoms we can also write the half equation like this you could see either of these versions of the equation in the exam but remember that they both show the same thing they both show two electrons being removed from an oxide ion to produce an oxygen atom now the second point is that the oxygen atoms formed at the anode pair up to form the oxygen molecule O2 so we need to double these equations like this Here's the final point about the anode the anode must be replaced regularly that's because the electrodes are made
of graphite and that's a form of carbon and these electrodes are around 900° C the oxygen molecules produced in the anode react with the graphite forming carbon dioxide gas I'm showing that reaction here now producing Metals by electrolysis is very expensive and there are two reasons for this which you need to learn firstly melting the compound such as aluminium oxide requires a great deal of energy secondly a lot of energy is required to produce the electric current remember you'll find plenty of questions on the extraction of metals using 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 describe why electrolysis is used to extract some metals you should then be able to describe how aluminium is extracted by electrolysis and finally if you're a high tier student you should be able to write half equations for the reactions at the cathode and at the anode [Music]
