AB Sir

Added: 2026-05-12

[00:00:00]now students you see that this weight of the reactant is 500 of the product is 499.99 which i took it as approximately 500. now definitely a question is coming into your mind let's say this 5 4 99.99 it is approximately 500 but it's not 500 so where that point zero one gram mass has gone where it has gone now this answer was not provided the landlord or by what you can say anthony lapsen so this is the like i should say this is a drawback or the limitations of this particular experiment okay so what you find is that that is einstein explained this particular thing einstein said that that here what is happening in ordinary chemical reaction this particular thing is not going to take place in ordinary chemical reaction ordinary this is an ordinary chemical reaction right this is an ordinary chemical reaction what you find is that here this particular ordinary chemical reaction that is almost it will be 500 gram almost it will be 499.99999 almost 20 degrees 500 in ordinary chemical reaction it is uh the mass the loss in mass is very very negligible very negligible it is very negative but listen carefully in some other reactions like some nuclear reactions the mass is being converted into energy all right now listen carefully what i said in other reactions that is in other chemical reactions like in nuclear reactions the mass is being converted the loss in mass is being converted into energy according to einstein's mass energy relationship that is e is equal to delta m c square but delta m is the loss in mass loss of mass means 500 minus 499.99 into that is c is the velocity of light 3 into 10 to the power 8 meter per second square what einstein said einstein said that you have stopped convection because by closing the airborne by making its airtight but we did not stop the radiation when the light is falling because you're doing this experiment in what you can say in sunlight or in order in light you will be doing this experiment in the lab so when the light is falling upon it some amount of energy is being radiated from the walls of the what you can say that particular landowned stew some amount of energy is being radiated out from the walls of the landords tube from the walls of the h2 that's a glass tube we can see that got it in the form of what you can say radiation so when some amount of energy is being radiated out so what is that the loss in mass is being converted into energy what i said i think it's clear to you that when that losses mass loss in mass has gone too that is 0.01 where it has gone that has been converted into energy according to einstein's mass energy relationship because when the light is falling upon that particular glass tube then the energy is being radiated out from the walls of the glass too energy is being given out from the walls of the glass tube in the form of energy it is being given up so hence there is a loss in mass but again i repeat this this reaction is only possible in a nuclear reactions or some other reactions but it is not possible in ordinary chemical reaction so einstein also added it that whatever the landowners and uh what you can say this uh anthony levis has said it's absolutely correct because they said on the light of ordinary chemical reaction ordinary chemical reaction the reaction which is occurring in your day-to-day life or with the one which you're doing it in the lab that is your displacement reaction double decomposition reaction decomposition reactions adhesion reactions all right for ordinary chemical reaction this is not been possible so this was the drawback of this particular experiment that is a law of conservation of mass so based upon that based upon that now the law has been slightly what you can say modified so what is being said that the lawyer said that the mass and the energy are interconvertible you know that mass and energy both are interconvertible as you can see there that mass is being converted to energy as mass and energy both are interconvertible but the total sum of the mass energy during any physical or chemical change remains constant what i said the mass and energy are interconvertible but the total sum of the mass and energy during any physical or chemical reactions remains constant all right this is the alternate definition now it has been given that is on the light of einstein's mass energy relationship otherwise when the definition will be asked to you for the law of conservation of mass the initial one which i i have told you that you will be writing it out i think it's clear to you the first law the law of conservation of mass fine now next is after that we'll come to the next law the law of definite proportion or the law of constant composition now what is that law of definite proportion or law of constant composition now this law i told you already it was given by joseph lewis prost jl proust so what is the definition of this law so the law states that in this way that when a reaction is taking place when a chemical reaction is taking place all right then what you find is that the uh product which is being formed the product which is being formed in any particular chemical reaction the ratio of the weight of the reactant is always constant the ratio of the weight of the reactant remains always constant all right so in this way you can say that in any particular reaction that is the mass of the product which is being formed right the mass of the product which is being formed the in the mass of the product the reactants which are combining to form the product that is a compound so the reactant always combines in a simple whole number ratio by mass and that particular ratio remains always constant all right that remains always constant we can say that okay fine now we will explain this particular one further by taking an example we can say that that is law of definite proportion we'll explain it see now so we are taking here that is calcium carbonate let us say on heating it gives calcium oxide plus carbon dioxide now we are taking calcium nitrate let us say on heating will give you calcium oxide plus nitrogen dioxide plus oxygen sorry 2 ca o plus 4 n o 2 plus root so in both the case you are getting calcium oxide let us say all right so now what you find is that that calcium is toxin what is said in the law that when a compound is being formed when the product is being formed the weight of the element which is being present here the ratio is always simple whole number ratio now calcium oxide what is the weight of calcium that is atomic weight is 40 and oxygen is how much it is nothing but 16 the 40 is to 16 so 2 into 8 2 into 22 into 4 2 into 10 then 2 5. so ultimately what is the ratio you got it 5 is to 2 so now here what i can say is that listen carefully in whichever source you can collect calcium oxide from whichever source you call it calcium oxide the ratio of calcium is to oxygen all right this is the ratio you got it for calcium is to oxygen the ratio of the calcium is to oxygen is always fixed in calcium oxide the ratio of calcium is toxin is always fixed that is five into two by wheat for example you are preparing carbon dioxide carbon plus oxygen gives co2 carbon monoxide bus oxygen will also give you co2 correct like calcium carbonate or heating also will give you co2 so the ratio of carbon is to oxygen in co2 from whichever source you collect from whichever source you collect that is the ratio will always be constant let us see this also carbon dioxide so carbon is to oxygen this is how much now here carbon is 12 oxygen is 32 so 4 into 3 4 into 8 so what we got the ratio three is to eight so from whichever source you collect carbon dioxide whether by heating calcium carbonate whether by heating carbon and oxygen whether by hitting carbon or oxide and oxygen from whichever surgical air the ratio of the element is always fixed it is constant here also it is being fixed its constant so we can say this in this particular way the definition we can say in this way also that any pure chemical compound listen carefully you may write this definition also any pure chemical compound regardless of its source always contains the elements in a fixed proportion by mass again i repeat any pure chemical compound regardless of its source contains the elements or combines the elements in a fixed proportion by mass we can say that or by weight we can say yeah so in this way i think it is clear to you that from whichever source you collect the source is not important all right it should be a pure chemical compound the ratio of the element in which the compound is being present the compound is being formed is always fixed it's always constant we can say that now to uh what you can say experimentally verify this law we will do an experiment we'll see an experiment okay are you following but i am saying i think you are getting me correct so now see here what we'll do is here we will take here copper carbonate and we will take here that is copper nitrate or heating now copper carbonate remember that it is green in color and copper nitrate it is blue correct so you will be heating copper carbonate you will get copper oxide and carbon dioxide okay and copper nitrate and heating will give you copper oxide plus nitrogen dioxide plus oxygen so we'll balance it this one you got it this now you got a black residue on heating both this green color substance you got a black residue with blue color substance you got a black recipe now you take equal weight of copper oxide from copper carbonate and copper nitrate let us say i have taken 20 gram of copper oxide whatever the weight you will be getting in here the residue from there you take 20 gram of copper oxide okay you take 20 gram of peroxide and through this copper oxide you pass a dry hydrogen gas or a current of hydrogen gas you pass it you hit it okay now what will happen hydrogen is a reducing agent it will reduce copper oxide to copper and water what do you how you know that the reaction has taken place like here you got a black residue you came through the reaction is taking place here you'll be getting a reddish brown colored residue or brown also you can select because copper is additional brown in color you can see so once you get this recipe you come to know the reaction is completed fine now what i said from both the source you take 20 gram 20 gram and you heat it and you pass it through hydrogen gas you will get copper now you weigh the copper from 20 gram how much copper 20 gram of copper oxide how much copper you want it to weight how did you weigh the copper from both the source are referring what i am saying 20 gram 20 gram each you have taken you are heated through hydrogen you got some copper you get some weight of copper now from copper oxide you subtract the weight of copper all right from 20 gram you subtract the weight of copper but you'll get the weight of oxygen first only you got the weight of what you can say copper now you got the weight of oxygen now you got what you can say to that is ratio you got it copper is to oxygen from copper carbonate the copper oxide which you got it and from copper nitrate the copper oxide you got it the two ratios you'll be getting the two ratios will be equal it will be same all right once once more i am saying you from here the residue which you got it you take 20 gram of copper oxide from it okay 20 gram heated this one each separately heat it you will get copper you take the weight of copper got it from both the source which you got it and you subtract from 20 you will get what rate of oxygen from copper oxide if you subtract copper what you'll get a bit of oxygen now you find the ratio between copper and oxygen what is the ratio from both the source which you will be getting the ratio will be the same all right it will be the same so from this experiment it is being verified that the ratio of copper is to oxygen got it from the different source which you are getting it is always remaining the same we can say that clear now but this experiment has also got a limitations now the limitation of this particular experiment is that now this particular uh vertical experiment is true or as i stick to carbon dioxide the experiment you can see that in case of carbon dioxide i got the ratio carbon is to oxygen how much is 3 is to it if you remember it i have taken the atomic weight of carbon as 12 if you remember it okay but now this law as i'm saying you the limitations of this law is that this law was true up to 19th century now after 19th century around 1913 we can say that sodi who was an english chemist who discovered isotopes after the discovery of isotopes what you find is that now here i have taken which isotope of carbon i've taken it is that carbon 12 but you know that carbon exists as c13 also and c14 of course they are not stable is the radioactive isotopes you must be knowing it of course they are not stable the stabilization is c12 all right so if you take c13 or c14 here the ratio will be different the ratio will be different for example what i am doing is that i am rubbing it first this one i am rubbing first so for example what i am doing carbon dioxide i am taking carbonate oxygen let us say carbon is 14 and oxygen is 32 all right here i have taken carbon so oxygen carbon atomic weight as 12. here i am taking it as 14. now see will it be same it will be different so here it will be 2 7 here is 2 16 so what is what the ratio 7 is to 16 now if you take carbon into oxygen i see 13 what do you get it 13 is to 32 all right 13 is to 32 is the ratio same here you got it 3 is to 8 here you got 7 is to 16 here you got 13 is to 32 the ratio is not the same so this law is valid for those elements which does not so isotopes but again i repeat here we will be taking that particular isotope only which is being stable so remember that c 6 c 12 is a stable accident 60 13 and 60 14 we are not taking it because they are not the stabilization all right but that is one of the limitations i said now this law is also not true when the compound shows what you can say isomers all right when it's so isomers isomers means now let us say you are taking the molecular formula of the compound as let us say c2h6o now c2x60 can exist as c2h5oh and it can exist as ch3o ch2 this is your ethyl alcohol and this is dimethyl ether you might have studied in class 10 isomers all right isomers to the compound having the same molecular formula but different structural formula we can say that all right so here is ethyl alcohol and here it is an ether enzyme so what i said that is here if i take higher alcohol and do the experiment if i take it i'll call into the experiment it will be different if i take dynamical ether and do the experiment it will be different all right because if there are two different compounds here it is two different compounds but the molecular form is the same got it if you take the molecular formula okay the ratio which you are going to get it is correct but if you take two different compounds if you take the structural formula then it will be different so again again the limitation of this noise that that this law is not valid for those compounds which shows isomers that means it is not valid for organic compounds because organic compounds show the isomerization so these are the limitations of this particular law that is a law of definite proportion or constant composition so again i repeat the log the definition that any pure chemical compound regardless of its source is always made up of the same elements combined together in a fixed proportion by mass the ratio remains always constant all right but again i repeat in carbon dioxide which i gave you the experiment and the that is there you must take the stable isotope all right you must take this stable isotope into it then you will get that answer to be as correct thank you