[Music] hi and welcome back to fre science lessons. co.uk by the end of this video you should be able to use moles to balance chemical equations this is for the higher tier only we've already looked at balance and chemical equations in a previous video in that video we used counting atoms to balance equations but in this video we're going to use moles it's fairly straightforward if you learn the method I'm going to start with an easy example this shows the reaction between hydrogen and chlorine to make hydrogen chloride the question tells us that 2 G of hydrogen react with 71 G of chlorine to make 73 G of hydrogen chloride we're going to use that information to balance the equation the first thing we need to do is calculate the number of moles of all of the chemicals in our reaction remember that the number of moles is the mass divided by the relative formula mass we've got 2 G of hydrogen and hydrogen has a relative formula mass of two this means that we've got one mole of hydrogen I'm going to show that by putting a one in front of the hydrogen like this we've got 71 G of chlorine and the relative formula mass of chlorine is 71 so that means that we've got 1 mole of chlorine I'm going to show that by putting a one in front of the chlorine like this okay we've got 73 G of hydrogen chloride and the reala formula mass is 36.5 so we've got 2 moles of hydrogen Chlor chloride and again I'm going to show this by putting a two in front of the hydrogen chloride like this now we're almost finished we've now got to look again at the large numbers we've got to make certain that these numbers are the lowest possible ratio to do that we divide all of them by the smallest number so in this case the smallest number is one starting with the hydrogen dividing one by one gives us one with the chlorine again dividing one by one gives us one and with the hydrogen chloride dividing 2 by one gives us two so as we can see these numbers are already the lowest possible ratio this means that this equation is now fully balanced all we have to do now is remove the number one in front of the hydrogen and the chlorine as we don't write one in chemical equations now you might be thinking what's the point of balancing equations using this method especially easy one such as this well this method works really well when the equation is more complicated such as this one 54 G of aluminium reacts with 216 G of ion 2 oxide forming 102 G of aluminium oxide and 168 G of ion balance the equation you should pause the video now and try this yourself okay first we need to calculate the number of moles of all of the chemicals and I'm showing you these here we've got two moles of aluminium 3 mol of ion 2 oxide one mole of aluminium oxide and 3 moles of ion now we've got to work out the ratio of these numbers by dividing by the smallest number in this case the smallest number is one 2 ided 1 is 2 3 / 1 is 3 1 / 1 is 1 and finally 3 / 1 is 3 so that means that these are our balancing numbers and we can put them into the equation like this remember that we don't write one in chemical equations here's a final example for you to try 1,248 G of berium chloride reacts with 684 G of aluminium sulfate forming 1,398 G of berium sulfate and 534 G of aluminium chloride balance the equation this looks tricky but it really isn't if you follow the method pause the video now and try this yourself okay first we need to work out the number of modes of all of the chemicals involved and I'm showing you these here we've got six moles of berium chloride 2 moles of aluminium sulfate six moles of berium sulfate and finally four moles of aluminum chloride next we work out the ratio by dividing all of these numbers by the smallest number in this case the smallest number is two 6 / 2 is 3 2 / 2 is 1 6 ID by 2 is 3 and 4 / 2 is 2 these are the numbers which we use to balance our equation so I'm putting them into the equation here and don't forget that we don't need to write the number one remember that you'll find plenty more questions on using moles to balance chemical equations in my Vis Vision workbook which you can get by clicking on the link above okay so hopefully now you should be able to use moles to balance chemical [Music] equations