okay so now I'm going to do a whole bunch of mole ratio problems a whole bunch so you can really get a handle on these they're super important for sto geometry for understanding story geometry okay each problem I'm going to do it two ways first I'm going to treat the equation the chemical equation kind of like uh kind of like a recipe all right where we've got our ingredients and then we've got the stuff we're baking this method really makes sense like you'll understand what you're doing but it requires a little bit of thought then I'll solve each problem using a conversion factor method the conversion factor method doesn't require any thought but it doesn't make any sense so it's really easy to get in the habit of only using the conversion factors running through the math but having absolutely no idea what you're actually doing or why you're doing it okay so that's why I'm going to do each of these problems two different ways okay so let's get started here is the first equation I'm going to be working with 2 mol of H2O water makes 2 moles of hydrogen gas and oxygen here if there's no coefficient in front of the oxygen in front of one of these chemicals we know that it's really one that it means one Mo so hey if it helps you go ahead and write that one in there's our equation here is the question how many moles of o2 of oxygen will be produced from 6.2 moles of water okay so first of all I want you to think of this like a recipe and right now it's saying that we start with two moles of this and that gives us two moles of this and one mole of this but we're not talking about starting with two moles of H2O we're talking about starting with 6.2 moles of H2O okay so this is just like when you're cooking and you've got a double or triple or quadruple recipe what do we have to do to this recipe so that instead of starting with two moles of water we start with 6.2 moles of water okay we have to multiply everything in this equation by something that's going to get us 6.2 moles of water we can figure this out a couple ways first thing that I can do is I can do uh 6.2 which is this divided two which is that and that gives me 3.1 okay that like gives me the factor and what I mean by that is that we take each one of these numbers and we multiply it times 3.1 2 * 3.1 and now we get 6.2 moles of this okay so now we're starting with 6.2 instead of two we multiply this by 3.1 now we'll also want to multiply the number of H2 times 3.1 so now we're getting 6.2 moles of H2 and we want to take this number which is one time 3.1 multiply it there and we get 3.1 moles of o2 so once again we treat this like a recipe in the kitchen that we're doubling or tripling instead of multiplying by two or by three or by four we multiply everything in this recipe by 3.1 we get 6.2 here so that's what we're starting with then we get 6.2 mol of H2 we get 3.1 moles of o2 and that kind of makes sense right because there's this two: one ratio of water to oxygen we start with two of these we get one of these so this is half of what we have here okay so if we start with 6.2 we multiply everything by 3.1 and we get 6.2 here and this 3.1 is half of what we had over here okay so that's how we can do this equation treating it like a a recipe in the kitchen now let's look at how we can do this using conversion factors okay what we're going to do is we're going to start with 6.2 moles of H2O now what I want to do is I want to write a conversion factor that tells me the relationship between the moles of water and the moles of oxygen okay we can sum it up with this it tells us for where every two moles of of H2O I get one mole of o2 two here one here okay we get this relationship and what I can do is I can use this to write a conversion factor there are two different conversion factors that I can get from this I can write 2 moles of H2O over one mole of o2 okay that's one or I can flip it I can do one mole of O2 over 2 moles of H2 of course I'm just getting the numbers from the chemical equation here two and one so I've got these two conversion factors that are Flips I could use either one of them they're both equally good the one that I want to choose though is the one that I can multiply by this and cancel out moles of H2O okay that's going to be the one that has H2O on the bottom because it's on the top over here so I'm not going to use this one I am going to use this one I'm going to multiply it here and now I have H2O on the top H2 on the bottom so they cancel out and when I do this math I'm going to do 6.2 * 1 / 2 = 3.1 moles of o2 and check it out I use a conversion factor method and I get the exact same answer that I got when I use this like a recipe okay so the recipe or the conversion factor both both give the same number okay let's go on to the next one okay so how many moles of H2O will be required to make 19.2 moles of o2 let's treat this like a recipe first okay right now this is a recipe for one mole of o2 what are we going to have to do to this recipe double it triple it quadruple it is what I mean what are we going to have to do to this recipe to make it a recipe for 19.2 moles of o2 well there's a one right here one mole of o2 in the recipe so it shouldn't come as a shock that we have to multiply the recipe by 19.2 and now if we multiply by 19.2 it will become a recipe for 19.22 time 19.2 and this is going to give me 38.4 moles of H2 multiply this by 19.2 because just like when you're cooking right you got to multiply everything in the recipe by the same number and this is going to give us 38.4 moles of H2O this is what happens to the recipe when we size it up to cook for 19.2 moles of o2 so the answer is how many moles of H2O are going to need we're going to need 38.4 moles of H2O that's the recipe method okay now let's look at the conversion factor method just as before we realize that the relationship between water and oxygen by using the chemical equation here is two of these to one to these so we can get these two conversion factors we have 1 Mo of o2 to 2 moles of H2O or 2 mol of H2O to 1 Mo of o2 I'm going to start here with 19.2 mol of o2 and I want to be able to multiply this by the conversion factor that's going to cancel out my moles of o2 so I'm going to choose this one here because it has moles of o2 on the bottom cancel out cancel out I do 19.2 * 2 / 1 equals 38.4 moles of H2O I know it's moles of H2O because that's the unit that I have remaining okay so sometimes people ask why are you doing it both ways why are you doing it the equ the the the uh recipe way and then the conversion factor way okay the reason is because for me the recipe way makes a lot more sense but teachers and textbooks are in love with conversion factors they love them they can't get enough I don't think the conversion factors make any sense at all all right but just because they're like commonly used your teacher's going to ask you to do it your textbook is going to ask you to do it that's why I'm doing them too but what I want you to focus on is actually why we're doing it the way we multiply things and get the answers here with pretending it's a recipe I want you to focus on this so you understand what's going on and as you can always see the answer that we get from the conversion factor method is the same as the the answer that we get when we're treating it like a recipe and multiplying everything by some number okay all right let's move on to the next question so 2 moles of H2S hydrogen sulfide combined with three moles of o2 oxygen to make two moles of so SO2 and 2 moles of h2l using this equation we're asked how many moles of o2 are needed to combine with 8.4 moles of H2S okay what do we have to do with our recipe to cook with 8.4 moles of H2S instead of uh two moles of H2S what we're going to want to do is we're going to multiply this by some number that's going to give us 8.4 how can we figure out what that is well you might sort of be able to do it in your head or you can do 8.4 / 2 and that's going to give us 4.2 2 so 4.2 is the number that we're going to have to multiply everything by so that we can move from two moles of this to a recipe that uses 8.4 moles of this okay so everything we're going to M multiply it by 4.2 okay so here we have 3 * uh 4.2 and that's going to give us 12.6 moles of of o2 2 to 3 8.4 to 12.6 all right let's see how we can do this using conversion factors we'll start with 8.4 moles of H2S and multiply that by one of these two conversion factors these conversion factors are just telling us the relationship that we have here of 2 moles of H2S to 3 moles of o2 and I can use this relationship to make these two conversion factors which one do I want to use I want to use the one that has H2S on the bottom so that it cancels out so I choose this one cancels out cancels out and this is going to give me what a shocker 12.6 moles of o2 why moles of o2 because it's the unit that's left here okay that's how we can do it treating it like a recipe here's how we can do it using the conversion factor here's an next mole ratio problem look maybe you're getting the hang of these maybe you feel great turn the video off then and move on to the next thing but if you still like some more practice hey let's party all night long with mole ratio problems we keep doing them until it feels really comfortable and you can and you're sure that you could like do any question that's thrown at you okay starting with 9.2 moles of o2 how many moles of H2S will you need and how many moles of2 will you get okay so starting with 9.2 moles of o2 right now our equation is written to start with three moles of o2 so what are we going to have to do we have to find out how to double triple quadruple whatever we want to do to this to get it up from three moles of o2 to 9.2 moles of o2 what am I going to have to multiply it by to turn this three into a 9.2 I can figure that out by doing 9.2 divided by three and I'm gonna get 3.1 so 3 * 3.1 is going to give me 9.2 I'm kind of rounding here all right if you do the math it's not exactly right okay anyway times 3.1 it's going to give me 9.2 moles of o2 and how many moles of H2 s am I going to need well I'm going to have to multiply everything in the equation by the same amount so times 3.1 here is going to give me 6.2 moles of H2S so that's how much H2S I'm going to need to combine with my 9.2 moles of o2 and then how many moles of SO2 will I get I take my 2 moles of so SO2 and I multiply that by 3.1 as well I've got to do the thing same thing to the whole equation and then I get 6.2 moles of SO2 so that's how we do that let's look at how we do the conversion factors you guys are really probably getting the hang of this now so I'm not going to show all of the conversion factor steps we start with 9.2 moles of o2 times what is our relationship between O2 and H2S we have 3 moles of o2 to 2 moles of H2S so I want to write that as a conversion factor with O2 on the bottom so that it cancels out so 3 moles of o2 to two moles of H2S moles of oxygen up here cancel out moles of oxygen down there cancel out and I get the same answer that I got here I get 9.2 moles of H2S and now let's just show how we can do this with the uh moles of so SO2 it's going to be the exact same thing I'm not even going to like get rid of this thing that's all canceled out here I'm going to multiply it by an equation that shows a conversion factor that relates oxygen here and SO2 here okay so again three moles of this to two moles of this so 3 moles O2 goes on the bottom and 2 moles SO2 goes on the top cancel this out already this is canceled out and I'm going to get after I do the math 9 .2 * 2 / 3 = 6.2 moles of SO2 sometimes I write moles with a knee sometimes M Mo because sometimes I get lazy any okay so that's that let's do two more if this feels good turn it off and move on so here we have an equation that talks about propane burning which is c3h8 nothing in front of this so we can put a one here one mole of this plus 5 moles of o2 gives me 3 moles of CO2 and four moles of H2O my question here asked me how many moles of oxygen are needed to react with 7.2 moles of propane what do we have to do to this equation to size it up so that we're starting with 7.2 moles of propane right now we're starting with one mole of propane okay so this isn't the hardest thing in the world we're going to have to multiply this whole equation times 7.2 and that's going to give us 7.2 moles of propane how many moles of oxygen are needed well we have to multiply it by 7.2 as well and that math is going to give me 36.0 moles of o2 let's look at the conversion factor method we're going to start with 7.2 moles of C3 h8 and we're going to multiply that by conversion factor that says one mole of C3 h8 to five moles of o2 which is going to be on the top which is going to be on the bottom this is on the top so we want this in the conversion factor to be on the bottom so I'm going to say one mole I'm getting it from right here one mole C3 h8 below five moles of o2 this cancels out it's on Top This cancels out it's on the bottom and it gives us 7.2 * 5 / 1 = 36 6.0 moles of oxygen okay one more our last one how many moles of propane are needed to make 13.5 moles of CO2 in order to do that how much O2 will be needed okay what do we have to do to our equation right now in order to make it 13.5 moles of CO2 instead of 3 moles of CO2 we're going to have to multiply it by some number that's going to move it from three up to 13.5 and what I can do is I can do 13.5 divided by three and that's going to give me 4.5 so I can multiply this by 4.5 and that'll turn my three into a 13.5 moles of CO2 so then when I'm talking about how many moles of propane am I going to need I'm multiply it by the same amount and I get 1 * 4.5 4.5 moles of C3 H5 and then I'm asked how much O2 am I going to need well I have to do the same thing to all the pieces of my recipe so 5 * 4.5 is going to give me 22.5 moles of o2 this is what happens to my recipe when I increase the size of it let me just show you these really quickly I'll start with uh 13.5 moles of CO2 times a conversion factor that talks about the relationship between propane C3 h8 and CO2 here CO2 is going to be on the bottom so that it cancels out so three moles of CO2 on the bottom one mole of C3 h8 on the top 13.5 Time 1 ided 3 is going to give me 4.5 moles of C3 h8 the number is the same even though the process is different oh what did I forget to do I forgot to cancel these out or I could I'm not going to get rid of it I'm going to just keep it there or to find out how much O2 I'm going to need well what is a relationship between CO2 and O2 it's 3 to five so 3 moles CO2 on the bottom and 5 moles of o2 on the top these cancel out 13.5 * 5 / 3 equal 22.5 moles O2 the same answer regardless of whether I do it the recipe method or the conversion factor method if you made it all the way to this end of this video you part with me all night long on mole ratios you're a rockar but more than anything I bet this really makes sense and I bet you can tackle any mole ratio problem that's thrown at you feel free to use the recipe method or the conversion factor method unless your teacher says that you have to use a conversion factor method then go ahead and use it but know in the back of your mind what is actually going on and why you're multiplying by what you're doing and all that sort of stuff all right all right good luck