 Hi everyone, today's topic is calculation of Molds, how can we calculate Molds? So, this Molds can be basically related to three things. One is when our weight will be given, we will be asked to calculate Molds. So, there are three subcategories we can say, either from weight or from number of molecules or number of atoms or if it is a gas then we can relate it to volume of gas in liters and STP or NTP. So, let's consider these three as three cases. So, case one, when weight is considered, weight of the substance is given. So, any Molds is equivalent to that particular weight that is given, how to calculate that? We already have seen that gram-molecular weight or gram-atomic weight is equivalent to our one Mold. Okay, that we have already seen that whenever we are talking about gram-molecular mass or gram-atomic mass we are talking about one mole of the molecule or one mole of the atom. So, let's take, let's continue with any one of them. Therefore, other one also it will be same. So, if I am talking about gram-molecular mass, let's say we are taking as molecular weight. We are denoting that gram-molecular weight as molecular weight grams is equivalent to one mole of the substance. So, one gram will be equivalent to how many moles? One upon molecular weight moles. So, now suppose of the same substance we are talking about substance X. So, that same substance is given to us but now let's say some different quantity is given. Y grams of substance X is given to us. So, one gram is equal to how many moles? One by Mw moles. So, Y grams will be equal to one by Mw which is the mass of one gram into Y mole. So, what did we do basically? If the molecular weight is equivalent to one mole, if one gram will be equivalent to one by molecular weight moles, then if suppose any Y gram is given to us. So, Y gram will be equivalent to how many moles? One by molecular weight into Y. So, from here one formula we are getting that is moles is denoted with N that is equal to weight, weight here is nothing but this Y upon molecular weight of the substance. So, this is a formula that we have got is our first formula for calculating moles when the weight of the substance is given to us. Now, coming on to the second case that is our case 2 when number of entities are given. Okay, capital N, capital N is number of entities. Entities can be atoms, molecules, anything. Now, we already seen that any number of entities is equal to one mole. So, one particular entity will be equal to how many moles? One upon any moles, one upon any moles. So, if I say I have N number of entities. So, it will be equal to how many moles? One upon any into N. Now, this we have considered as entities. We will see for both molecules and atoms now. So, if we have N A number of molecules that means we have one mole of molecules. Okay. So, one molecule will be equivalent to how many moles? One upon N A. So, suppose we have N number of molecules. So, N number of molecules will be equivalent to one upon N A into N. So, from this one more formula we are getting that is N is equal to N upon N A. So, this is our formula where this N represents what number of molecules? So, if suppose they are asking how many number of atoms will be present? Suppose they have given a molecule H2O. Let's say they have given two moles of H2O and they are asking how many number of atoms are present in that? So, using this formula you are finding what? Number of molecules we are finding. So, N is equal to N upon N A. So, 2 is equal to N upon N A. So, N will be what? 2 N A. So, this 2 N A is what? 2 N A is the number of molecules of H2O. But if we are asked number of atoms then one molecule contains how many atoms? That means I am asking you the atomicity of H2O. One molecule of H2O contains three atoms. So, 2 N A molecules will contain how many? Three into 2 N A atoms. So, please note when we are talking about 6 N A atoms. When we are talking about molecules then this N represent molecules only. So, if in that question you are asked number of atoms then definitely you have to multiply this N with the atomicity in order to find out the number of atoms. But if they tell atoms only like if they say N A number of atoms. If they talk about atoms itself then N is equal to N upon N A. They are this particular N is nothing but atoms itself. Because from the very beginning whatever moles is given that is depicting atoms only. Right? Okay. So, here one more formula we have got. What formula we have got? N is equal to capital N upon N A. So, this is our second formula that we have got. Now, third case. Third case we can relate the moles with volume of any gas. If it is gaseous then we can relate moles with the volume of gases in litres at standard temperature and pressure. Now, here in this case three definitely we are relating moles with volume in litres. Of gas STP. What is STP? Standard temperature and pressure. What is standard temperature and pressure? Standard temperature and pressure is pressure is equal to 1 bar. Temperature will be 273 Kelvin. And when we will calculate the volume keeping this pressure as 1 bar and temperature as 273 Kelvin the volume will be coming around 22.7 litres. Okay. Now, this was the first one that is STP. Second one is NTP. NTP is normal temperature and pressure. Normal temperature and pressure. So, normal pressure is 1 atmosphere and temperature will be 273 Kelvin. So, when we calculate the volume keeping these values the volume comes as 22.4 litres. So, in case of STP the volume is 22.7. In case of NTP the volume is 22.4. One more condition is there that is SATP. Generally in the question this SATP will not be given. STP and NTP will be given. So, at that time we will take the volume as 22.7 or 22.4 accordingly. But what is SATP? Standard ambient temperature and pressure. So, at standard ambient temperature and pressure pressure will be 1 bar and temperature is taken as 298 Kelvin. So, when we calculate the volume the volume will come around 24.6 litres. So, based on what condition is given STP, NTP or SATP the volume will keep on changing. We are talking here about 1 mole for everything we are talking about 1 mole. Now, how it will relate to mole? Here when I say 1 mole it means that if we consider this STP then 22.7 litres of gas at STP is equivalent to at STP is equivalent to 1 mole of the gas. So, 1 litre will be equivalent to 1 upon 22.7 moles. So, suppose any XYZ volume is given of any gas. So, volume I am taking as any value, volume at STP some value is given. So, that particular litre will be equivalent to 1 upon 22.7 into volume that is given at STP in litres. Why litres? Because here also this value is in litres. So, if it is in ML do convert it into litres first. Or if you are using this volume in ML then you have to change this also to ML. So, it will become 227.00 ml. So, one more formula we have got relating to volume of gas that is nothing but N is equal to volume in litres at STP divided by 22.7. So, this is another formula to calculate moles when volume of gas in litres at STP is given to third formula. So, total three formulas we have got. Now, we will club all these formulas. N is equal to W by molecular weight or atomic weight both we can say if it is a molecule then molecule gram molecular weight if it is atom then it is gram atomic weight. N is equal to N upon NA and N is equal to volume in litres at STP upon 22.7. Now, I can equate I can relate all these three formulas together as N is equal to W by MW that is equal to N upon NA and that is equal to volume in litres at STP of any gas upon 22.7. All these are interrelated I can relate N with this N with N by NA N with volume by 22.7. I can also relate weight entity and number of molecules. I can also relate weight with volume I can also relate number of entities with volume. So, all these are interrelated so we can use it accordingly. So, this particular formula is very very important so any value can be given for example N can be given and they can ask you weight. So, at that time you will liquid only these two and molecular weight we will gram molecular weight we will be knowing NA we know and we can easily calculate weight if N number of molecules or atoms are given. Now, quickly we will do one question before we move forward. This is the question that is given so we have to calculate the number of more. Let's do the first one the first one states that we have 2224 grams of SE that means W is given as 224 grams and what is the gram molecular weight gram sorry this is not molecule this is one atom of iron so here it will be gram atomic weight. So, gram atomic weight of iron is nothing but 56 grams so what will be our moles N is equal to W upon 8 am so 224 upon 56 that will give you a answer of 4. I would like you to pause the video and try the second and third before smashing your answers please do try yes. So, the second one states that we have this many amount of atoms number of atoms so N is given here N is atom only because they have mentioned oxygen atoms. So, N is given as 12.044 into 10 to the power 24 and we know NA is equal to 6.023 into 10 to the power 23 so just we have to put it in the formula which formula this formula. So, N is equal to N upon NA put the values 12.044 into 10 to the power 24 upon 6.023 into 10 to the power 23 then you will calculate this how much will you get around 20 moles this will be the answer for the second one. Third one how many liters of neon at STP is given 5545.4 liters so this is our volume liters at STP so what will be our N? N will be equal to volume upon 22.7 so that is nothing but 45.4 divided by 22.7 that is nothing but 2 moles. I hope you could do it on your own we will practice more numericals but before that we will draw we will we will see how to remember this three formulas in a efficient way. So, there is something which is known as YMAP YMAP YMAP helps us to remember how to calculate moles from different different entities that will be given. So, let's say we have moles. Now first one was our first we related moles with weight this is our weight now whenever we need to weight whenever weight is given and we need to calculate moles from weight then what should we do? We should divide this weight with atomic gram atomic mass if it is atom or we should divide it with molecular weight if it is a molecular if it is a molecule. Now suppose moles is given and we need to calculate the weight then what should we do? We need to multiply it with atomic weight if it is atoms or we need we need to multiply it with molecular weight if it is a molecule. So, from weight to moles and moles to weight this is the thing that you should do if weight is given and we need to calculate moles we have to divide it with the weight of respective atom or molecule and if moles is given and we need to get weight then we have to multiply with the respective weight that is given. Now next entity with which we have connected moles is our number of entities if number of entities that is our n is given and we need to find out moles then we need to divide that n with Na but if moles is given and we need to find out the number of entities then we have to multiply it with Na multiply home multiply the moles with n so when we are going from moles to n we have to multiply with avogadro's number. Coming on to the third one that is our volume in liters of any gas volume in liters of gas at STP so suppose again if volume is given and I want to get moles I want to calculate how many moles are there in that particular volume of gas that is given then I need to divide it with 22.7 and suppose moles are given and I need to find out in that particular moles how much volume in liters of the gas is present then I need to multiply it with 22.7 so whatever formula we have written at the top this one this particular formula you can remember in the form of a wire map that is shown over here this is very very important for few people whichever like you feel is comfortable for you to remember you can go with that wire map or that chain formula that I have shown right now there is an important concept I hope you have taken and one more important thing I hope you are taking notes of your own see this thing just by listening this won't work you have to make your own notes in order to understand things much more clearly so I am hoping that you are taking down everything taking note of everything that is a very good practice yeah coming on to the next topic there's a very important topic rather a concept is the volume of what is the volume of 1 mole of an ideal gas just now we have written volume of 1 mole of an ideal gas is equal to 22.4 liters or 7 liters at NTP or 22.4 liters at NTP now when we are converted into meter cube then we have to multiply it with 10 to the power minus 3 meter cube it will be ok now radius of now we are calculating this for hydrogen atom what is the radius of hydrogen atom let's take it as R that will be equal to now diameter of hydrogen atom is 1 angstrom ok 1 angstrom we will see we will study about this in structure of atom but for now you just note down that it is 1 angstrom so radius will be 1 angstrom by 2 so that is coming around 0.5 angstrom that is equal to 0.5 into 10 to the power minus 10 meter converting everything into meter I have converted liter also into a meter meter cube so here also we have converted into meter now volume of 1 hydrogen atom will be volume of a sphere right fourth third pi R cube so it will be fourth third into pi into 0.5 cube into 10 to the power minus 30 meter cube so this we have already made cube and have written 10 to the power minus 30 this is the volume of one hydrogen atom so what will be the volume of any hydrogen atoms the volume of any hydrogen atoms will be this entire term into N so that will be fourth third pi 0.5 cube into 10 to the power minus 30 into 6.023 into 10 to the power 23 meter cube right so when we calculate this entire thing so when we are talking about NaH atoms we are talking about 1 mole of hydrogen atoms so volume of 1 mole of hydrogen atoms when we calculate this entire thing we get it around 3.15 into 10 to the power minus 7 meter cube so this is the volume occupied by hydrogen 1 mole of hydrogen atoms but ideally what should be the volume of 1 mole of an ideal gas it should be 22.4 into 10 to the power minus 3 meter so if I say this is a container this is this volume is around 22.4 into 10 to the power minus 3 meter cube definitely 1 mole of each atom should occupy all this volume but what is the actual volume of the each atoms it is this much so if we compare these two volumes if we compress all the each atoms together at one corner it will be around this much it is almost negligible negligible the volume of NaH atoms is almost negligible to the volume of the ideally how much volume it occupies so from here we can conclude that there is a lot of space the intermolecular space between the gas gas molecules is very very large so if I find out a ratio ratio between the volume of volume occupied by 1 mole of ideal gas and the actual volume of the 1 mole of each atoms it will be 22.4 into 10 to the power minus 3 upon 3.15 into 10 to the power minus 7 it will come around 7.1 into 10 to the power 4 so this ratio is very very large and what does it depict it depicts that it proves rather that the intermolecular space in gases is very very large so basically it should occupy this much amount of space but as recall there is large amount of space inside the like between the gas molecules it is occupying a large amount of volume this much amount of volume it is occupying so I hope you have understood so basically whatever if you if you try to subtract this amount of this volume from the entire volume it will be almost negligible the subtraction part will be almost negligible so almost the entire part is our vacuum space okay so I hope you have understood this now that why the intermolecular space is so much large and yes that's all for today and next class we will be seeing certain numericals we will be practicing a lot of numericals next class in the next video will be solely on practicing numericals thank you for watching the next class