welcome to another episode of Terry's notes and today we are going to be looking at the extraction of metals when a metal is extracted from its allil the process is a reduction process for example extracting aluminium from the o aluminium oxide or boxid the if we want to extract aluminium from this oil the reaction that is taking place is al3+ plus three electrons produces aluminium cuz remember if we have a boxid is Al 23 the aluminium has a three plus charge and the oxygen has two minus charge all right now if we look at the oxidation state of aluminium it changes from plus three to zero all right because in the aluminium ion we see it has a a tri plus charge and in the aluminium solid the oxidation number is zero so therefore we have a a decrease in oxidation number and this is called a reduction reac reaction so therefore aluminium the aluminium ions are being reduced now metals can be extracted by electrolysis of the molten o it can be extracted by heating the o with a reducing agent for example carbon or carbon monoxide or it can be extracted by heating the O at high temperatures now what determines the choice of extraction method the choice of extraction method of a metal is determined by its position in the reactivity series now you need to find a way to remember the reactivity series at the top we have the most reactive element which is potassium and at the bottom we have gold so reactivity decreases down the series or we can say that reactivity increases up the series so at the top potassium is the most reactive and at the bottom gold is the least reactive and we usually put in hydrogen as a reference within the reactivity series now at the top we have the most reactive metals this means that the ores or the compounds formed have very high melting points and therefore requires a strong method of reduction so at the top of the reactivity series we have to use electrolysis in order to extract the metal at the bottom the least reactive these elements can exist as free elements meaning that you can just be mining and you can extract gold or it can also be extracted from the OE by heating strongly and anywhere in the middle of the reactivity series we have to heat the or with a reducing agent for example carbon or carbon monoxide right so just remember that the position in the reactivity series is what determines the method of extraction so let's go back to what we were saying what determines the choice of extraction the most reactive metals in the activity series form very stable OES and therefore requires a strong method of reduction therefore electrolysis is a choice of extraction the least reactive metals in the activity series can can exist as free elements for example gold and metals that lie between the most reactive and the least reactive form relatively stable ores however they can be extracted by heating with carbon uh or carbon monoxide Okay so let us first look at the extraction of aluminium and this is one that you required to know so you need to know the O that we are using okay first thing so the O is aluminium oxide you need to know the formula it's al23 and is also referred to as boide so we can get boide from Jamaica and also from Guyana and the method now remember aluminium is at the top or it's very reactive and the aluminium oxide is very stable so therefore the method of extraction is electrolysis you need to be familiar with the steps in the electrolysis process so the first step is to purify the O so you're going to have the aluminium oxide you just need to purify it to get pure aluminium oxide Second Step the purified o is dissolved in molten cryolite and the formula for that is N3 alf6 so it's dissolved in molten cryolite at 950° C now why do we do that the melting point of aluminium oxide is is very high 250° C right why is it very high because aluminium oxide is an ionic compound and you have al3 plus ions and O2 minus ions so the bond or the electrostatic force that exists between the oppositely charged ions are very strong and that is why it has a very high melting point so we said we we take the aluminium oxide and we dissolve it in molten cryolite at 950° C now a large amount of energy would be required to melt the aluminium oxide on its own mixing the ore in molten cryolite allows the electrolysis to take place at a much lower temp temperature you need to notice because sometimes you are asked why is aluminium oxide dissolved in molten cryolite The Next Step electrolysis is carried out using graphite electrodes so this diagram shows how the process takes place so we have a large steel tank and we have the molon cryolite and the molon aluminium oxide as the O we have the graphite anodes that is this and this and this and the steel tank is also lined with graphite so all right and this lining is a code and these carbon or these graphite rods are the anodes now you need to know the two reactions taking place so at the code remember the cathode is negatively charged so therefore the al3+ ions are going to move towards the cathode so the AL 3+ is going to move towards the cude and the reaction taking place would be al3+ plus three electrons produces aluminium at the anode now we have remember we have O2 minus these are going to move towards the anode and the reaction taking place is 2 O2 minus minus 2 electrons produces oxygen gas now what is happening is that you notice we have bubbles being produced at the anode now the oxygen produced at the anode reacts with the graphite so remember graphite is carbon carbon plus O2 produces CO2 to so what happens over time is that the anodes have to be replaced because they are being used up or they are being the mass of the anodes are decreasing now the other extraction we need to be familiar with is the extraction of ion in this case the O is Ion Tre oxide and the formula is Fe 203 and another name for it is hematite now if you recall where ion is in the activity series it is somewhere in the middle so the method of extraction is the reduction of the O using carbon carbon monoxide in a blast furnace okay now the steps in the extraction of iron First Step a mixture containing ion Tri oxide calcium carbonate which is known as Limestone and Coke which is carbon is added at the top of the blast Blast Furnace so basically you have the blast furnace looking like this we have we have the O ion trioxide calcium carbonate and Coke being added at the top of the Furnace we have heat here and we say it's a blast furnace because a blast of hot air is blowing at the bottom of the furnace all right now what you need to be familiar with familiar with is the reactions taking place so the first thing the coke which we said was carbon reacts with oxygen to produce carbon dioxide so C plus O2 produces CO2 and this reaction is exothermic the second step or the second reaction taking place is that the carbon dioxide reacts with more carbon to produce carbon monoxide this is an important equation here but this reaction is endothermic now next reaction taking place is Fe2O3 plus 3 3 Co produces 2 Fe plus 3 CO2 so you have the ion Tre oxide reacting with the carbon monoxide to produce ion and carbon dioxide so this equation shows how we produce the ion make sure you familiarize yourself with this so the first thing carbon reacts with oxygen to produce carbon dioxide then the carbon mon carbon dioxide reacts with more carbon to produce carbon monoxide and it is the carbon monoxide that reacts with the ion trioxide to produce the ion okay so carbon monoxide is the reducing agent not the carbon dioxide and the molten ion flows out at the bottom of the Furnace now how do we treat with the impurities now a major impurity in the O is silica or sio2 and the high temperatures inside the furnace causes the Limestone to decompose to form carbon sorry to form calcium oxide okay so remember we added calcium carbonate at the top which is limestone so when we heat calcium carbonate we produce calcium oxide and carbon dioxide now the calcium oxide reacts with the silica to form calcium silicate which which is slag so CAO plus S2 produces cao3 and this layer floats on the molten ion and is tapped off so this is how we treat with the impurities okay um si2 is acidic and calcium oxide is a base all right so just a Miz the position in the activity series is what determines the method of extraction at the top of the reactivity series we have the most reactive elements and they form very stable oos and therefore we have to use a strong method of extraction and therefore we use electrolysis for those elements at the bottom of the activity series these are the least reactive elements and they form they usually exist in their free state for example gold if they do exist as a compound you just have to heat it strongly and you'll extract the metal and metals in the middle of the reactivity series can be reduced using carbon or carbon monoxide and the two extraction methods that you need to be familiar with is the extraction of aluminium and the extraction of I ion the extraction of aluminium is done by electrolysis and the extraction of ion is done using the using carbon monoxide as a reducing agent