hey guys hope you're well so this lesson is all going to be about this formula over here so the n stands for mole the now you see there's a small M and there's a capital M don't confuse those okay so the small m is the mass or let's say the given Mass okay this will all make sense when we do some examples that's the given mass and then the capital M is called molar mass okay and what that is is it's the mass on the periodic table and it's measured in grams per mole so you write it like that okay this will make sense as we do some examples so what I want us to do now is answer the following question so this question says how many moles are there in 88 grams of CO2 okay now by the way this given mass is also measured in grams so what we can do is we use this formula over here okay so we set n equals to M over capital M now look how easy this is they gave us 88 grams so that is the small M the small m is the given mass and so you're going to say 88 over now to calculate this part over here this is the mass on the periodic table so if you look at CO2 well what we can see is that that is going to be one carbon atom okay so it's one carbon atom plus and then there's two oxygens over here so two oxygens okay and so that would be one carbon atom which has a mass of 12. and then two oxygens would now oxygen has a mass of 16. so if you work this out correctly you should get 44. and then remember that the units of capital M would be um grams per mole so you're going to say grams per mole and so you're gonna go put that number down here at the bottom and then if you had to calculate this you're going to end up with two mole so here's another example and then as we go along in this lesson I'm going to give you more questions like this but then I'm also going to start changing the questions up where you're going to have to start using this formula in different ways so it says how many moles are there in 54 grams of H2O okay so we're going to say n equals to M over capital M now remember that the small m is the given Mass the Big M is the molar mass which is from the periodic table and then n is the mole so we're going to say uh n is equal to another given mass is 54. that's what they gave us 54. now the molar mass you have to go get that on the periodic table so this is H2O so that means um the the molar mass of H2O would be there's two hydrogens there's two hydrogens and there is one oxygen one oxygen and so the mass of that would be 2 multiplied by one plus 1 multiplied by oxygen which is 16. and if you had to work that out you would get 18 and then the the units is grams per mole so I need to say I need to say 18 grams per mole so I put a 18 over there and if you had to go work this out you'd end up with three mole here's another one so how many moles are there in 49 grams of h2so4 okay so we know that to calculate moles you're going to say n equals to M over capital M now remember small m is the given Mass which must always be measured in grams and then the capital M is the molar mass which is the mass that you get on the periodic table and then n is the mole okay so the given mass is 49. now h2so4 so what that is is um to work out the molar mass of h2so4 well there is um two hydrogens so two hydrogens there is one sulfur atom okay so let's just write that a bit better one sulfur atom and four oxygen atoms four oxygens and so to work out the mass that would be two times one because each hydrogen has a mass of one um one multiplied by sulfur's mass which is 32 and then four oxygens each oxygen has a mass of Sixteen and if you had to go calculate that you end up with 98 now the units of that is grams per mole so you could put 98 over there and if you had to go calculate that you're going to get 0 comma five Mo now in the next questions I'm going to show you um the next question coming up after this one how to change this formula and use it in different ways okay so let's do that so what we can do is we can make a triangle so you know the triangles that I've showed you in previous chapters like maybe in electricity we've got these triangles where we've got a v i r or maybe you've seen other ones like WV and Q or maybe you've seen uh q i and T for example now when we have triangles like that it makes it easier to work with them okay and to do different things so here you see this one's at the top so the one that's at the top is always the top part of the triangle okay and then the other two you could just put at the bottom so the end you could put there and then the capital M you could put there so now you could make a whole bunch of different formulas let's say you're trying to get this one by itself well we know that if that one's at the top then the other two at the bottom are next to each other so you would multiply them like that okay or maybe you want to get this one by itself well that one you wouldn't really need to get because that one's the one that's on the periodic table okay but let's just say maybe they gave you a weird question uh where oh no I don't think they'll do that so don't worry about that one and then obviously to work out this one over here oh no let me actually go back to this one they could sometimes do something weird where they give you like a made-up molecule that is not on the periodic table and then they ask you to calculate this part well to do that you'll just say um this is at the top and this is at the bottom so that's at the top that's at the bottom and then lastly if we need to calculate this one well we know how to do that one already because this m is at the top and then the Big M is at the bottom and then you just get back to this formula over here okay so you need to know how to use all three of these and so for the remainder of this lesson I'm going to give you some questions um that's going to help you practice the different types so here's our next question so it says determine the mass in three moles of CO2 okay so we know that we've got these formulas okay now we know that n stands for mole the small m stands for mass or given Mass if they give you a mass and then capital M is the molar mass now remember that the molar mass is the one that is on the periodic table so they want us to calculate the the the mass not the molar mass that just means the normal Mass so that's this one okay so we need to get a formula with this one and so that's over here and so we could say that that mass is equal to the number of moles multiplied by the molar mass so that's going to be equal to 3 because they said there's three moles multiplied now the molar mass is from the periodic table so to calculate the molar mass of CO2 well there is going to be one carbon atom one carbon atom and then there's going to be two oxygen atoms so the mass would be 1 times 12. plus 2 times the mass of oxygen which is 16 and that's going to give you 44 grams per mole so you can put 44 of here and if you had to go work that out you would end up with 132 grams oh just like that yeah you're just going to say 132 grams you're not going to say grams per mole the only time you say grams per moles when you're working out the capital M which we've just done here on the periodic table so for this one you just say grams okay let's do some more examples this one says determine the mass of 9 mole of NaOH so if we have our triangle over here then if they want us to calculate mass well that's this one over here so that's going to be n multiplied by capital M okay so we're going to use that formula and so the number of moles is nine and then to get the um to get the sorry you need to get the mass on the periodic table so n a whoopsie why am I writing so weird n a o h well that's going to be 1 in a atom you can see one in a plus one oxygen plus one hydrogen plus one hydrogen and so that's going to be the mass of n a 23 the mass of oxygen 16 and the mass of hydrogen is one so that's going to be 40 grams per mole and so we could say 9 times 40 and that's going to be 360 grams here's our last question so it says how many moles are there in 50 grams of CaCO3 okay so if we have that triangle then they want the number of moles now so they want this so number of moles is equal to whatever's at the top divided by the capital M which is molar mass so they remember that n is Mo m is the given Mass and here they've given it to us and then capital M is the molar mass molar mass which is on the periodic table periodic table so we're going to say n equals to M over capital M and so the mass is going to be 50. to go work out the molar mass of calcium carbonate or CaCO3 then that's going to be one calcium atom one calcium plus one carbon plus three oxygens okay and so that's going to be one calcium which is 40 grams per mole plus one carbon which is 12. plus three oxygens now each oxygen is 16. so if you had to go calculate this you get a hundred grams per mole so that's going to be over a hundred and so if you had to go work this out you're going to end up with zero comma five mole