Hi everyone, welcome to Vedanta Neat English. I am Diksha Kaushal, your chemistry master teacher. So guys, firstly, so sorry about being late. It was not my mistake, okay.
Power cut happened in my locality and that's why I was rescheduling the class. But now, thank God, I don't have to reschedule it again. And I am very happy that our class is today itself.
It's not rescheduling to Sunday. I am very happy about it. Yes, so hi everyone, welcome, welcome, welcome, how are you all and are you excited for our chapter, first chapter of your class 11 that is some basic concepts of chemistry.
Right everyone, are you all ready? Yes, bacha, are you all ready everyone? And also share this with your friends, right, share this with those who are in need of these kind of lectures, right, who want to practice. who want to practice from the base right so sharing is caring as I always say that don't feel like this is basically a healthy competition right it's not like oh my god that person will go ahead of me but that person will not go ahead of you right you both will learn and you will compete with each other in a very healthy environment right otherwise anyway somebody out there is working more hard right anyway someone why not that somebody be your friend and you both compete in a very healthy environment right yes but okay so are you already everyone green hearts in the chat box for the show ma'am green hearts in the chat box for chemistry everyone yes already shared ma'am very good very good ma'am I am ready for your student ma'am I am already your student in DNA batch okay very good but are very good amazing I think in DNA batch so we have completed this chapter in like 7 to 8 lectures I have taken each and like I have taken every topic for like 1 to 2 hours in detail right ok so yes but for DNA batch students also this will be very amazing because here I have picked up NS of any NS of the questions so that you can practice right it's for DNA batch as well as for those students who are not in DNA batch both of the students that will be very helpful right yes bicha Yes, bacha. Okay, shall we start?
Shall we start everyone? Okay, perfect. So now as you can see, as you can see here, mole concepts, stoichiometry, limiting reagent, empirical and molecular formula, right?
We are going to do all these things. Just a minute. We are going to do all these things today, right?
Okay. So now starting with mole concept. Firstly, we are going to start with mole concept. Mole concept is related to stoichiometry. Stoichiometry, if you don't know stoichiometry, you will not be able to understand limiting reagent and after that empirical and molecular formula is also related to number of moles formula, right?
So, for that firstly we need to get into detail of mole concept, right? Firstly, let us start with mole concept, right? So, students to understand mole concept, to understand mole concept, we need to understand what is exactly atom, right? So, as you all know that For example, this is a matter.
For example, I am saying this is a matter. Okay, this is a matter. Okay, this is a matter. Right?
So what is matter made up of? Everyone, what is matter made up of? Everything around us is matter that occupies any space and volume.
That is matter that we have studied in our lower classes. Right? So now let us see matter is whatever we are seeing. Whatever occupies a volume. For example, this air also.
I cannot like touch the air like that. I cannot hold the air in my hand, right? But that air, the molecules of air has some volume. They have some mass. And that is the reason they are also matter, right?
So matter is made up of very tiny, tiny particles, okay? Matter is made up of very tiny, tiny particles. And bacha, these tiny particles, These little little tiny particles are nothing but they are called atoms. They are called atoms.
Yes. What they are called? Atoms.
Yes, bacha. Okay. So, now let us see in atoms when we talk about atoms.
It is the smallest. Now, it is the smallest unit, it was said. But after that, after we know that there are subatomic particles like electrons, protons and electrons. But in the Dalton's atomic theory, beta, in Dalton's atomic theory, in Dalton's atomic theory, Dalton's atomic theory, right? In Dalton's atomic theory, the postulates were as below.
First postulate was. that atom is indivisible. Atom is indivisible. It cannot be divided. This was the first postulate.
Right? But now in current situation that is a wrong statement. Right?
Because now we know that this is actually wrong but atoms are made up of subatomic particles like electrons, protons and neutrons. right that we are going to study a structure of atom that is the second chapter right that we are going to study second chapter right okay yes very good now second what was the second postulate second postulate of Dalton was that atom follow I would say just simply I would say it was in accordance with Law of conservation of mass. He said that atoms before the reaction and atoms after the reaction will be same. That means the mass before the reaction and the mass after the reaction will be same. That means mass cannot be created nor be destroyed.
That was nothing but our law of conservation of mass. mass right okay third law was in accordance with in accordance with in accordance with which law in accordance with in accordance with bacha in accordance with the law of definite proportion law of definite proportion right law of definite proportion now this stated that the number of atoms For example, H2O I am talking about. Now H2O, wherever you take H2O, water from a pond, ocean or you can say from your RO, right? Anywhere, the H2O will always have 2 molecules of hydrogen and 1 molecule of oxygen, right?
Carbon dioxide is always going to have 1 carbon and 2 oxygen. Always and always, right? Okay, now... Don't worry, we are going to study these laws of chemical reactions, chemical combination in detail, right? But not today, in some other class, right?
We are going to study that in detail, right? With examples and questions, right? So the fourth, the fourth postulate, that was same element, same element will always have same mass. Everybody here, tell me if that is true.
in today's world or not right and the fifth postulate was different different element different element always have always have different Mars right everybody in the chat box yes that is not true when it comes to when we talk about today's in today's world this is not true Right? This is not true. What is the reason? The reason is isotopes. Right?
What are isotopes? Isotopes are you have carbon, you have carbon 14, you have carbon, you have carbon 13, you have carbon 12. Right? You have three isotopes of carbon.
Similarly with hydrogen, similarly with oxygen, oxygen 16, oxygen 18. Right? That means Same element can have different masses. That was according to isotopes. That is the definition of isotopes. So if isotopes exist, that means this particular postulate is not true.
Right? What about this one? Different element, different mass.
Is that true or not? Is that true or not? That is also false because of isobars.
Okay? What are isobars? For example, which have same atomic mass. but different elements, right?
For example, Argan and Calcium, right? Same atomic mass, but different elements are there, right? But different elements. Right?
Okay, bicha? Yes, everyone? Now, now, this also you can say that, I think, yeah.
So, different elements, different, for example, nitrogen 40, carbon 40. Now, these are different elements. This is an isotope of carbon. These are different elements, but the mass is same. So, because of these isobars, this postulate is also wrong.
Right? That was about Dalton's atomic theory. Right? So now we understood that what is atom.
Right? So after this, then we understood that after Dalton understood that what is atom. Now we have to understand how to calculate the mass of atom. Right? So the next part was how to calculate, how to calculate mass of atom, mass of one atom, one atom.
Right? So you He observed that the mass of a single atom is in 10 raised to the power something like 10 raised to the power minus 24, 10 raised to the power minus 27. Now these kind of masses are very difficult to learn. These are the absolute values, okay? These are the absolute values.
Absolute values are very difficult to learn. They are approximately 10 raised to the power minus 24 grams, right? Now these kind of powers.
For example, students, we have elements. How many elements, bachcha, we have? How many elements we have in periodic table? We have 1, 1, 8 elements in the periodic table. And is that possible to learn absolute value of 1, 1, 8 elements?
Not possible, right? So, to make it easy for you, to make this thing easy for you, that you don't have to cram all the values, they adapted a method, right? They adapted a very simple method in which in today's life you know that hydrogen is atomic number 1, hydrogen has mass number 1, ma'am carbon has mass 12, ma'am oxygen has mass 16, ma'am nitrogen has mass 14, right? We all know this today, right? In today's life we all know this thing.
But how it was calculated? How? How it was calculated?
That we need to understand, right? This is not the absolute mass. This is not absolute mass. This is not absolute mass, beta.
Because absolute mass is in these kind of hours. 10-24 is the absolute mass, right? These kind of hours.
Now, to make it into one digit, we have to compare it with something, right? For example, now what is the difference between absolute and relative? absolute and relative, absolute and this is relative, right?
Now, see, absolute is something, for example, your marks are 95, you have 95 marks, okay? You have 95%, right? That is your absolute marks, that it is not dependent on any other thing, it is not dependent on how much your best friend has scored, your 95% is only dependent on your hard work, right?
Okay? That is absolute. That is dependent on only you. But what is relative? Relative is you are second in class.
Second position in class. Right? Second position in class.
Now this will be dependent on others as well. For example, if someone has scored 96%, then you will be 95% will be second. Right?
If someone has scored, if no one has scored above 95%. 95%. Then you will be at first position.
That means, this is what happens in ranks, right? This is what happens. Your marks in NEET, for example, if someone has scored, if someone has scored 650 marks, right?
That is only his or her marks, right? That is not dependent on any other thing. But right now, NT is making it dependent on other things as well.
Otherwise, it is not dependent on anything, right? But now, something else is going on only, right? But... Your relative, your relative, that means your cutoff or say your rank is dependent on others, right?
It is dependent on others, which rank you will have, right? It is dependent on how many students have scored above 650, how many students have scored above you, right? So that is the difference between absolute and relative.
That means this is only yours, right? This is In comparison, this is in comparison. Now, they thought of comparing it.
They thought, okay, we don't want absolute mass. We want relative mass, right? We want relative mass, which is we see, which is we see relative atomic mass, relative atomic mass, which is also called as Ram, okay?
Arayam relative atomic mass, right? Now, so many discussions were going on, okay, what you want to do, what you want to do, like, okay, so many discussions were going on. And they all were thinking, what to compare it to, right?
So, they all thought that let's compare it with hydrogen, right? Let's compare it with hydrogen. They're like, okay, very nice.
Hydrogen is a very chotu motu element, like very small element. Yes, we can compare it. But the problem here was, the problem here was, All the masses were coming out to be in fractions. Okay, that was a problem.
They were like, if we want masses in fraction only, why don't we learn absolute mass only? We are learning, we are making a new quantity here that is relative atomic mass. Because we want to learn the digital values. We want to learn simple integer values. We don't want to learn 0.001, 0.002.
No, we want simple values, right? Okay. So that means fraction is not our thing, right? So we neglected it.
Second students, second was, second was, anybody? Anybody in the chat box? Second was, to your surprise, it was oxygen, okay? It was not carbon, it was oxygen, right?
They thought, okay, after hydrogen, oxygen is a very abundant element. We all are here because of oxygen. We are breathing oxygen, right?
It is a need of our life. That means oxygen, let's compare it with oxygen. Like okay fine, let's compare it with oxygen. Now what happened? In all like throughout the, through internationally, it was said that let's compare it with oxygen and values were given.
And values of all the other atomic masses were given. But Chintu in India is thinking that okay, they are comparing it with oxygen number 16. And Minto in Australia. He is thinking that maybe they are comparing it with oxygen number 18. Now they got confused. Right? Chintu Vintu got confused.
They were fighting with each other. Right? That no, they are talking about oxygen 16. No, they are talking about oxygen 18. Now what to do? Then it was adapted that okay, let's fix it to oxygen number 16. Now the union, the international union, they told that we are talking about oxygen 16. We are not talking about oxygen 18. Okay fine but there are so many confusion was there because of this particular thing right they were telling everybody that we were talking about oxygen 16 but still there was confusion right so they thought let's let's neglected okay they refused this also they refused this also now they thought okay let's take one more element which is very very famous that is carbon because of carbon only organic chemistry exists right So they said okay let's compare it with carbon.
Let's compare it with carbon. Okay after comparing it with carbon. Now they are like we are not going to repeat the mistake again.
Right. We are not going to repeat the mistake again. They said we are talking about carbon number 12. That's why whenever you write it.
Whenever you write the definition. You always write carbon 12 isotope. Carbon 12 isotope. You never write. carbon isotope or carbon 13 isotope or simple carbon it was always written carbon 12 isotope okay that is the reason now here they were like okay we are going to accept this because we have made it very clear that they are comparing now with carbon number 12 right bicha okay yes okay bicha chal now it is clear to you that ma'am they are comparing with carbon number 12 now let us see there was one unit That is a relative atomic mass.
What is relative atomic mass? The name was given to be, the name is given to be atomic mass, mass unit, right? Very, very important. Atomic mass unit, that is AMU, right?
That is AMU, atomic mass unit. Now, let us talk about what is this atomic mass unit? What is this atomic mass unit?
The definition of AMU is C. You have a box. You have a box. 1, 2, wait.
You have a box. Break it into 12 compartments, okay? Break it into 12 compartments, right? 1, 2, okay? 1, 2, 3. Now, 4, 5, 6. Again, 3 into, I think 1, 2, 3, 4, 5, 6, 7, 8, 9. We need one more compartment, okay?
We need like this, okay? So, this is your 12 compartments, right? This is your carbon 12. This is your carbon 12, okay?
Right? This is your carbon 12. Now, they fix the mass of, they fix the relative mass of carbon 12 to be, fix the relative atomic mass of carbon 12 isotope to be 12, right? It is 12 in this atomic mass unit, in this AME, right? They fixed it to 12. Everybody, this is very, very important.
Students get confused, right? In this particular thing, right? So...
they fixed the mass of carbon 12 isotope as 12 amu right they gave a new they gave they gave birth to a new unit that is atomic mass unit that is to calculate the mass of one single atom right one single atom so they said that the mass is 12 amu that means these 12 compartments are 12 amu now if we want to calculate the value of one amu students you If we want to calculate the value of 1 amu. Right? For example, these total are 12 boxes.
12 boxes. If we want to calculate the mass of 1 box, what we will do? We will divide it by 12. Right? We will divide it by 12. That we will do. Right?
So, this is what we are going to do here also. We are going to divide it by 12. And that is going to be 1 amu. Now, students, this is your 1 amu.
Right? If this total 12 compartments is carbon 12, then students, this is your 1 amu. Right?
This particular, this pink box is your 1 amu. That is 1 by 12th of mass of carbon 12 isotope. Right, bachcha?
Is that clear to everyone? Is that clear to everyone here? Till here? Everyone that is clear? Yes?
Yes bacha write it in the chat box Are you not able to hear? Or any problem here? What happened to you all?
Nobody is responding here. What happened, son? What happened? Right?
Are you sleeping or what? Be a little active here. Otherwise, there is no use of that I am teaching.
Right? Be a little active here. Right?
Otherwise, there will be no fun in the class. It is just going to be a very boring class. I don't want to behave like a robot here. Right? I don't want to behave like a robot.
Yes, be active in the chat box, okay? Otherwise, it is going to be such a boring class, no? Such a boring class it is going to be. Yes, okay? So, that is your atomic mass unit, that is this one, right?
Now, let us understand atomic mass unit. The atomic mass unit is equals to 1 by 12th of mass of 1 atom of carbon-12 isotope. That is the mass of 1 atom of carbon-12 isotope, right? Now...
Very important thing. Now what is students 1 AMU? Very very important. What is 1 AMU? 1 AMU is 1 by 12th of mass of 1 carbon 12 isotope.
Mass of 1 carbon 12 isotope. Everybody in the chat box what is the absolute mass of carbon 12 isotope? Everybody in the chat box what is the absolute mass of carbon 12 isotope? You put the absolute mass of carbon 12 isotope you will get this value that is 1.66.
1.66 into 10 raised to the power minus 24 gram, that is nothing but 1 AMU, right? That is nothing but 1 AMU, right? Okay? That is nothing but 1 AMU, okay?
Yes, bacha? So, that is your mass of, that is your value of 1 AMU, right? That is very, very important.
Now, You need to always remember this particular value. You will see questions based on this, okay? You will see question based on this particular value. Now, next part is, what is the relation between absolute mass and relative mass? Right?
Absolute and relative mass. Right? So, always and always students, whenever they ask you, whenever you put the relative atomic mass, for example, for example, there is a question based on this. There is one question based on this.
Let me show you that question. Let me show you that question. Wait. I think I'll just wait for a minute.
Right. So, for example, students, I'm talking about H2O or I'm talking about oxygen, oxygen atom. Right. Oxygen atom. You know, the mass of one oxygen atom is 16U.
Right. The mass of one oxygen atom is 16U. This is the relative, this is the relative atomic mass, this is relative atomic mass. If they ask you the mass of one oxygen atom, one oxygen atom in grams, mass of, mass of one oxygen atom in grams, which are in grams or this is also the absolute, absolute mass, absolute mass, right? So how you will calculate it?
You will simply multiply this by, you will simply absolute mass, absolute mass is going to be 1 mass of 1 oxygen atom in atomic mass unit multiplied by 1 amu, multiplied by 1 amu. That is going to be 16 multiplied by 1.6 into 10 raised to the power minus 24 grams. Okay.
You just put the value of 1 amu. now you will be able to calculate the value in grams, right? So, there are few few little little things that you need to understand here, right?
Here, bacha, this is not one mole or Avogadro's number, nothing I have told you here, right? Here, I am just telling you how to calculate the mass of one atom, single atom, okay? If they ask you the mass of atom in AMU, that is simply 16, okay? For example, for nitrogen, it is 14, right?
For sodium, it's 23. Right, for calcium it's 40. Right, simple mass that you remember. Right, now if they ask you the mass of one atom in grams, you just need to multiply it by 1 amu, that is 1.6 into 10 raised to the power minus 24 grams. Right, okay. Now students, let us understand what is Avogadro's number. Because if we want to understand mole concept, firstly we need to understand Avogadro's mole and all the formulas here, only then we will be able to understand mole concept.
Right, so now bacha, What is Avogadro's number? For example, we all know that when we talk about one dozen, right? One dozen, that means 12 bananas that we are talking about, right? Similarly, that is a fixed quantity, right? If I say one dozen, you already know Mamni is talking about 12 bananas, right?
If I say half dozen, you already know Mamni is talking about 6 bananas, right? So, similarly students, when we talk about Avogadro's number, that is a fixed number, that is 6.022. into 10 raised to the power 23 particles ok particles these are the Avogadro's number that number is fixed ok that is 6.00 into 10 raised to the power 23 particles now these particles now which are these particles can be an atom it can be a molecule it can be an ion it can be any electron or proton or proton or neutron anything that is called particles if I see if I see students I have this is firstly this is mentioned by any ok I will get rose number is mentioned by n and somewhere in the subscript in the subscript it's a right and now students if they talk about that you have any amount of any of H2O.
That means you have 6.022 into 10 raised to the power 23 molecules of molecules of water, right? That means you have this much molecules of water. Now, students, if they talk about, if they talk about Na of O2, right? That means 6.022 into 10 raised to the power 23 molecules of Molecules of O2, right?
And if they talk about Na of oxygen atom, Na of oxygen atom, that means they are talking about 6.022 into 10 raised to the power 23 atoms of oxygen, right? That means they are talking about this much atoms of oxygen. oxygen and from this particular thing from this particular thing you can also say that if they are talking about this much molecules of O2 and O2 is diatomic in one molecule you have two oxygen atoms then you can say it has 12.4 12.044 that is 2 multiplied by N A into 10 ish per 23 atoms of oxygen Right?
Atoms of oxygen. Right? And students also here, in this particular thing. Here students, wait, wait, wait.
Yes. Now everyone, you tell me in water, I told you about water here, right? For this water, how many hydrogen atoms are there?
How many hydrogen atoms are there? Here students, in one H2O molecule, In one H2O molecule, you have two hydrogen atoms. So in these many hydrogen, in Avogadro's number of molecules, you will have 2 into Avogadro's number of hydrogen atoms. So that will be 12.044 into 10 raised to the power 23 hydrogen atoms. Okay.
If they talk about oxygen, in one molecule of water, you have just one atom of oxygen. That means here you can see 12.044 into 10 raised to the power, no, no, no, it will not be like this. It will be the same number of atoms.
So it will be 6.022 into 10 raised to the power 23 oxygen atoms, right? Okay, Vicha? Yes, everyone.
That is clear. Yes. So now let us understand what is one mole. Now let us understand what is one mole, right?
1 mole is nothing but when we say 6.022 x 10 raised to the power 23 particles that is 1 mole. That is 1 mole. If we talk about in numbers it is called these many atoms and if we talk about in moles, in 1 mole you always have Avogadro's number of particles.
For example, if somebody is asking you that 2 mole of O2, what does that mean? 3 mole of 3 mole of an atom, what does that mean? Now students see this, 2 mole of O2, this means that you have Evergadro's number of 2 into Evergadro's number of 2 into Evergadro's number of right 2 into Evergadro's number of oxygen molecules right because in one mole you have Avogadro's number that is Na.
So in two moles you will have 2 into Avogadro's number right. Okay similarly 3 moles of nitrogen atom means you will have 3 into Na of nitrogen atoms right. That means 3 into 6.022 into 10 raised to the power 23 nitrogen atoms right. This simply means 12.044 into 10 raised to the power 23 O2 molecules. Right?
O2 molecules. Yes, bacha? Okay? Understood this part? So, simply we can say that 1 mole means 6.022 into 10 raised to the power 23 particles.
That's it. That is the definition of 1 mole. That is what we call 1 mole. Right? Okay, kid?
Now, this is called 1 mole. Avogadro's number is 6.022 into n raise power 23. 1 mole is the Avogadro's number of particle is 1 mole. Right? If in one bucket, if in one bucket I am carrying, if I am saying, if there is a rule, if there is a rule, that one dozen bananas one dozen bananas are 12 one dozen means 12 bananas right and you can only carry one dozen banana in one bucket in one bucket right so that bucket that bucket is mole that bucket is mole that dozen is Avogadro's number Avogadro's number Avogadro's number and those 12 bananas are the number of number of particles right or number of bananas right okay so even if you say one bucket even if I have fixed that that in one bucket you can only have one dozen bananas that is 12 bananas so even if i am saying if i am saying i am carrying one bucket of banana that means that means 12 bananas if someone is saying i am carrying one dozen bananas he is also saying 12 bananas if someone else is saying i am carrying 12 bananas he is already saying 12 bananas that means these three things means the same thing whether you are talking about one mole or one ever get rose number or you are talking about 6.022 into 10 raised to the power 23, you are talking about the same number.
You are talking about the same number. Yes, bacha? We are talking about the same number.
Yes, bacha? Bacha, wait, wait. Wait for 2-3 minutes.
You will be able to understand that as well. Right? Now, next part here is, ma'am, there are so many masses. So many masses, ma'am.
Oof, ma'am. What to do, ma'am? Ma'am there is gram atomic mass, gram molecular mass, molar mass, molecular mass, atomic mass, relative atomic mass, absolute atomic mass, so many average atomic mass, formula atomic mass.
Now what to understand? So many masses, what is the difference? How to calculate these?
Okay, very simple, okay. Now we have differentiated between relative and absolute atomic mass, right? Okay, now let us see what is gram atomic mass.
Gram atomic mass is nothing but they are talking about one mole of atom. They are talking about one mole of atom. That is gram atomic mass.
Right? The units are, units are gram. Okay?
So, students, if I talk about, so students, if we talk atomic mass atomic mass atomic mass of oxygen atom right and if we talk about gram atomic mass gram atomic mass gram atomic mass of oxygen atom or if we talk about atomic mass Or you can say mass of, not atomic mass, mass of 1 mole of, 1 mole of atom, right? 1 mole of atoms. Or you can say mass of, mass of Avogadro's number of atoms, right? Now let us see what is going to be the answer here.
Let us see what is going to be the answer here. Yes, bacha? Let us see what is going to be the answer here. Yes everyone, now see this very carefully everyone. Now atomic mass, atomic mass, atomic mass of oxygen atom, what is that?
They are talking about one atom, they are talking about one atom. Whenever someone is talking about only one atom, right? That will, you will calculate the mass of that atom that is 16, right? You will mention U here or you can also mention 16 amu, right? That is about one atom only you are talking about.
When you are talking about gram atomic mass, gram atomic mass, the numeric value will be same. The numeric value is same. Oxygen atom, oxygen atom, numeric value is same. The difference is here in place of U, you will write gram, right? Because here we are not talking about one atom.
We are talking about 6 into 10 is per 23 atoms. That is the numeric value will be same. There will be difference of U and gram here.
right what about mass of one mole one mole is nothing but gram atomic mass again 16 gram right you can also see 16 gram per mole right that is also right mass of Avogadro's number of particles that is again bacha that is again that is again that is again nothing but they are talking about gram atomic mass again 16 gram right ok that is clear that is clear now Let us talk about molecule. Let us talk about a molecule. What is a molecule? A molecule is like this.
Okay. This is a molecule. This is a molecule.
If I talk about one atom, this is one atom. Okay. This is other atom. Right.
This is other atom. We all are atoms. Okay? Different, different atoms. But when they combine together, they form a bond.
We will see that in chemical bonding. They form a bond. They together, they are chemically bonded with each other.
Now they formed a molecule. This is called a molecule. Right?
This is called a molecule. Now in molecular mass, what you will do? You will add on to all the masses of atom.
For example, students, for example, this is a This is a molecule, this is for example, let us talk about, let us talk about, okay, let us talk about this particular molecule, right? Let us talk about this particular molecule. This is 2 hydrogens and this is 1 oxygen. What is the mass of 1 oxygen? That is 16, right?
Now, 1 hydrogen is bonded to it, 16 plus 1, mass of hydrogen is 1, right? Atomic mass of hydrogen is 1, right? Now, two hydrogens are attached to it, that means this is your H2O, this is the molecule of water, right, this is how it looks like, right, so the molecule of water has one oxygen, two hydrogen, 16 plus 2, 18, right, that means in a molecule, you add the, you add the atomic masses, you add the atomic masses, right, for example, if I am talking about the molecule of NH3, There is a molecule of H2SO4, right?
There is molecule of, then you have CH4, right? Okay? Then you have NH2CUNH2, right?
How to calculate the molecular mass? How to calculate the molecular mass? Just add the atomic masses. Because, bacha, I am just talking about one single molecule. I am not talking about so many molecules.
Just one molecule. Right? So I will add the atomic masses. Right? So here what I will do?
The molecular mass. The molecular mass. It's not molar mass. It's molecular mass. The mass of one molecule.
Right? The mass of one molecule. Mass of, mass of one molecule. Mass of one molecule. Right?
Now that will be, this is going to be nitrogen is 40 plus 3 into 1 is hydrogen. That is 14 plus this is 17. What is the unit here? Unit is U. You know earlier it was atomic mass unit only. Atomic mass unit was adapted for atoms.
But you cannot write for molecular mass. You cannot write AMU, right? So that is why we write U here, right?
We write U here, right? In place of AMU. What is H2SO4?
That is 2 plus 32. 2 plus 32 is the mass of sulfur that you have to remember, okay? So, what about oxygen? That is 6 into 4, that is 64. 64 plus 32 plus 2, that comes out to be 98, right? That is 98U. Yes, bacha?
Now, what about CH4? This is 12 plus 4 is the mass of 4 into 1. 1 is the mass of hydrogen, right? So, 12 plus 4, that is 16U. I am again repeating, it's you, you, you, okay, when we are talking about just one thing, that is you, right, not G, right, so that is NH2CO, NH2, you can also remember this by when there is group of, group of people coming to attack you, you say, G, G, G, G, G, I am so sorry, G, I am so sorry, G, you give them respect, okay, you are like, oh my God, they have come to attack us, right.
Like when all the social media influencers and educators attacked NTA they were like GGGGGG right so when you are a single person nobody is there for you then they are like you please go right so that is when you are single then it is you go when there is group of people they are GGGGG whatever you say whatever you say right so that is G for Avogadro's number of molecules for one mole molecule not for one single right. So here what about urea bacha? You have 2 molecules of 2 atoms of nitrogen plus beta you have 2 molecules plus 4 is for hydrogen plus carbon is 16 plus oxygen is 16 plus 12. Right? How about this one?
This is 28 plus 28 plus 4 that is 32 plus 16 plus 12 that comes out to be this is 10, 3, 4, 5, 6, 7 I think 70 70 Yes, 70 if I have done the calculation right. Yes, 3, 4, 5, 60. So sorry. That's what I was thinking. 70 is to not the mass.
That is 60. Right? Okay. Now, this was the molecular mass.
We have already done that. Right? Next, bacha, you have gram molecular mass. That is for 1 mole.
Right? That is for 1. That is for 6.022 into 10 ish by 23 molecules. Right?
That is gram atomic mass. So, simply what we are going to write, we are going to calculate the. Atomic mass we are going to calculate the gram molecular mass sorry gram molecular mass we are going to calculate the gram molecular mass ok gram molecular mass just write here gram gram molecular mass ok what you do just replace U with G ok just replace U with the G G G G G okay G, G, G, G, right?
So, everyone here G, G, G, G, that is the mass of one mole, the mass of 6.022 into 10 raised to the power 23 molecules, right? The collection of molecules, then we are saying G, okay? Now, next part is last one that is similar to gram atomic mass and gram molecular mass, right?
That is same as gram atomic and gram molar mass. This means one mole of one mole of particles right here they are not specifying they're not specifying that we are talking about atoms or molecules right you're talking about particles so that can be atoms or molecules right that can be atoms or molecules for example the molar mass of the molar mass of the molar mass of O2 and the molar mass of molar mass of oxygen atom right for 6.022 into 10 raised to the power 23 oxygen molecules it is 32 gram per mole right it is gram per mole usually it should be written as gram per mole but in some books it is written as gram also that is not wrong okay so molar mass of oxygen atom is One oxygen atom, that is 16, right? Because we are talking about Avogadro's number, that will be 16 gram per mole, right? Okay? Yes, bacha, any problem till here?
No, any problem in masses? Now, what is formula mass? Formula mass is for ionic compounds. This is for ionic compounds that is not that much detail in your syllabus right. So basically ionic compounds exist as a lattice structure right.
What is lattice structure? It's like this okay. It's like this. This is a lattice structure.
This is a lattice structure. So they basically exist as a lattice structure right and here what we see that for one cation how many anions we need. For example Why NaCl is called NaCl?
Why it is not Na2Cl? Why it is not Na3Cl? Because for every 1 Na positive, 1 Cl negative was required.
Right? That is why we have made a jodi NaCl. And what about AlCl3? What about AlCl3?
For this, for every Al3 positive, 3 chlorine ions were required. Right? For every 1 Al3 positive.
3 chlorine ions were chloride ions were required that is why it is AlCl3 right that is why it is AlCl3 and any other anic compound you can talk about right but yeah AlCl3 has a very different structure that we will study in a p block right this is just an example right I would not advise you to write it okay let's write something else right for example MgCl2 let's write MgCl2 not AlCl3 Because it has a dimeric structure, right? That we will study in P block, right? Okay?
So, yeah. Let's talk about MgCl2. That is Mg2 positive and 2 Cl negative are required for that. And that is why it is MgCl2.
That means for every cation, how many anions are required? For every anion, how many cations are required? Right? Okay? Now, bacha, last is average atomic mass.
What is average atomic mass? For example, I will give you an example of this. For example, you have an element, you have an isotope A, isotope B, isotope A and isotope B.
An element, element you have two isotopes A and B. Okay, you have two isotopes A and B. The abundance of or you can simply write, you can simply write M1 and M2. That is isotope. The abundance of that is the percentage in which M1 exist is A1.
And the percentage in which M2 exist is A2. Right. So, how do you calculate the average atomic mass?
How do you calculate the? average atomic mass that will be that will be students and one that is the isotope number one right what is the mass of isotope this is the mass ok m means mass ok m means mass a means abundance right the mass of isotope number one multiplied by abundance of isotope number one plus mass of isotope number two multiplied by isotope abundance of isotope number two divided by 100 that is the what is this beta that is what we call that is what we call is the that is what we call is the average atomic mass right this is what we call is the average atomic mass for example you have magnesium right it has atomic number 24 let's see 25 let's say 26 let's say okay and just wait wait wait let me see if I'm writing the question right or not just give me a minute I think the abundance of this one is the abundance of this one was 79 percent the total of this one is 21 percent right the total of this one is 21 percent Just give me a minute so that we can actually see, right? Okay.
You have to calculate the average atomic mass, right? You have to calculate the average atomic mass. Not average atomic mass. Wait, wait, wait.
Okay, I think the mass of the average atomic mass, just give me a minute, okay, in that question, the average atomic mass was given, okay, the average atomic mass was given. Let me see if I can find that question. Really hoping to find that but not sure about it.
I think I won't be able to find that. No worries, no worries, no worries. I'll just take an example.
I'm giving you arbitrary value here, right? Okay, I'm just giving you random value here. So average atomic mass comes out to be 24.8 gram.
Right? That is your average atomic mass. Now you have to find the abundance of magnesium 25 and magnesium 26 that you have to find out right that you have to find out though how will you find out this how you will find out this right how you will be able to find this out this is just one thing why I have told you this why this question is here because there is one important part about this question when very important part that part is that here the total average of the they are saying that magnesium number 25 right and magnesium 26 they total have 21% abundance right so if you take the abundance of this to be x this will be 21 minus x that's it okay that is why I have taken this question so here the answer will be here the answer will be average atomic mass that is 24.8 equals to 24 into 79 percent plus that is you Here it is x abundance that is 25 so it will be 25x right here it is 26 and the abundance is 21 minus x. divided by 100 you just have to solve the value of X here and 21 minus X that is your abundance of magnesium 25 and magnesium 26 that is why this question is very very important because students what they do they take the abundance of 25 to 26 is 21 percent what they do they will say okay ma'am that will be the what some students what they do they do 25 plus 26 Here the abundance is 21%.
That is totally wrong. Okay. They are giving you the total abundance of these two isotopes. Right. So take it as X and this is isotope 21 minus X.
Right. Okay. Now next students next next next is mole concept.
Now as I already told you for mole concept first thing is very important. That is one mole of any particle is 6.022 into 10 raised to the power 23. Of that atoms or molecules or ions or electrons of that particular species. Right?
So, can we say that one mole for calculating mole, we can divide it into three things. Okay? There are basically three methods of calculating mole.
Three methods of calculating mole. Right? Everywhere you will write given.
Bi-molar, given bi-molar. Here also write given bi-molar, given bi-molar. Here also write given bi-molar.
Here also write given bi-molar. Okay, given bi-molar. Now students, given bi-molar, here you can write when we want to calculate the number of moles with the help of mass.
Write it here, given mass by molar mass, right? Given will be given to you in the question, okay? That will be given to you in the question. Now, given, when we want to calculate in terms of particles, that is atoms or molecules, then you will write given particles, given particles, given particles by molar particles, by molar particles, right? When we want to calculate it with the help of volume, that is given volume by molar volume, given volume by molar volume, right?
Okay? So, bacha, one molar mass. Molar mass is so different for all the atoms or molecules or what is given to you in the question. That is not a fixed value. That is fixed for one particular atom or one particular molecule.
Right? So, we can't write a fixed numeric value here. Right?
But molar particles are fixed. That is Avogadro's number. That is Avogadro's number. So, simply here write, simply here you write N A. That is the... I will get dros number of particles, right?
And what about this one? Given volume will be given to you in the question, right? What about molar volume, beta?
That is also fixed, okay? Molar volume is also fixed. What is molar volume?
That is 22.4, right? And this is in liters, okay? This is in liters. And always remember one thing, that when beta, this is at STP, okay? This is at STP, at STP, right?
When we are talking about pressure is 1 atmospheric, right? But students, if nothing is given to you, no STP, nothing is given to you, you will take molar volume as 22.4 only, right? If no pressure is given to you, it is not specified, you will automatically consider it as 22.4. But if they say 1 baric, this is very rare chance, rarest of rare chance and this doesn't even matter, right? But still in calculation this doesn't even matter.
But if they have given pressure to be 1 bar, then students molar volume will be 22.7. Right? Okay?
This will be hardly apply anywhere. Right? Okay? Yes? Very good.
Now, this was your mole concept. That means students, can we say that if I want to calculate number of moles, I can calculate by this method. Either this method or this method. Any method I can apply here.
Any method. Right? That is mole concept. Now, let us see the questions based on this.
Right? So that concept can be more clear to you. So, first students, the question is, 1 AMU is equal to, everybody in the chat box, 1 AMU is equal to, what is the value of 1 AMU?
1.6 into 10 raised to the power minus 24 grams, 6.022 into 10 raised to the power 23 grams, that is so definitely not, right, definitely not, right, then none of these, no, right, 1.6 into this kilogram, no, right, it is 1.66 into 10 raised to the power 22. 24 grams, right? So, answer is A is the correct answer, right? Next part students, next part we have the mass of one molecule of HNO3. One molecule, bacha. The mass of one molecule.
It is given in grams, everybody. It is given in gram, kilogram or it is given in AMU also, right? Now, let us see. Now, let us see what is correct and what is not correct, right? Now let us see what is correct.
What is HNO3? What is HNO3? One molecule of HNO3 molecular mass is 1 plus 14 plus 16 into 3. That is 1 plus 14 plus 48. Right? That is 48 plus 15. That comes out to be 13456. That is 63. Right? That is 63U only.
Right? 63U. Now that means B is the correct answer, is it?
Should I take it B? No, no, no, no, no. B is definitely the correct answer. But if I calculate it in grams, okay?
If I calculate it in grams, 63, what is the value of 1U or 1AMU? That is 1.66 into 10 raised to the power minus 24 grams. That means this is also true. That means this is also true. And if I want to calculate it in grams, if I want to calculate it in grams, that will be 63 into 10 raised to the power 1.66 into 10 raised to the power minus 27 kilograms.
That means this is also true. So, answer is all of these is true. Okay.
All of these is true. Okay. All of the above is true. Right.
Okay. Yes. Now, next question students.
What is the number of moles of oxygen atom in 126 AMU of HNO3? Now students, don't apply simply mole concept here. It is written 126 AMU, okay? It is written 126 AMU. That means some 1 or 2 or 3 or 4 molecules is given to you.
So let us write mass of 1 molecule. HNO3. What is that?
Mass of one molecule of HNO3 is what we calculated it as 63u. Right? How many, how much mass is given to you? 126. That means 126, 126 beta. Number of molecules, number of molecules here will be.
For example, I am telling you, you have One chocolate, right? One chocolate, the mass of one chocolate is 50 grams. Okay?
The mass of one chocolate is 50 grams. And then I am telling you that total, I am giving you 100 gram of chocolate. Tell me how many chocolate I am giving you. You will say, ma'am, obviously two chocolates. Right?
Ma'am, you are giving me double the amount. That means two chocolates. So, that means what I did, I divided the... mass that I told you, that is, I am giving you 100 gram of, I am giving you 200 gram of chocolates, okay, I am giving you 400 gram of chocolates and one chocolate weighs 50, so now tell me what will be the answer, right, what will be the answer students, right, what will the answer, answer will be 8, right, 8 chocolates I am giving you, right, similarly, here how many, how many, how much mass is total, right, that is 126. right that is 126 so in this much of this right and one molecule has mass of 63 right so divided it will be two molecules it will be 2 molecules and now they are saying you need to calculate the number of moles of oxygen atom right now you know in one molecule in one molecule of HNO3 you have three Molecule, 3 atoms of, 3 atoms of oxygen, right? Or I can just write it in the other page.
1 molecule, 1 molecule of HNO3 has 3 molecules, 3 atoms, 3 atoms of oxygen, right? Can you multiply by NAC? Number of moles is equals to number of moles.
Number of moles you have to calculate, right? So number of moles to calculate number of moles just simply write if you have one molecule has three molecule three atoms then two molecules of HNO3 will have six atoms. Six oxygen atoms, right? And in the question, what we are given with two molecules, right? Two molecules we calculated.
So, in two molecules, you have six atoms, six oxygen atoms. But they are not asking you the atoms, they are asking you the number of moles. So, number of moles of oxygen atom, that is going to be the number of atoms divided by Avogadro's number, right? So, it is going to be 6 by nA.
The answer is going to be D. The answer is going to be D here, right? Answer is going to be at a 0 C.
That is the number of oxygen atoms. They are asking you the number of moles here, right? All these questions are from N-A-V-S-T, okay? So, they are asking you the number of moles here. So, number of moles will be 6 by N-A, right?
Okay? Yes? Now, next question, beta. Next question.
calculate number of oxygen atom in 126 gram of HNO3 always remember whenever you are calculating the number whenever you are applying the mole concept right what you do you firstly write it throughout today I would I am going to write this two things what is given to me what is asked to me what is given to me what is asked to me what is given to you information about this thing is given to me perfect right And what is asked to me? Number of oxygen atom that is asked to me. This is given to me. This is asked to me. Given, asked.
Given, asked. So what I do? From given, I will start the question. Always, always you will see throughout this lecture I am going to do this.
Right? Given, you will see moles. Firstly, calculate the moles.
Right? Either moles will be given to you or any other hint will be given to you to calculate moles. That can be, they may give volume, right? So, if they give volume, you will apply that volume formula that is V naught by V by 22.4, right? If they give you particles, that is molecules, you will apply the number of molecules divided by Avogadro's number equals to mole.
If they give you mass, that will be given mass by molar mass, right? Any method you can apply to calculate the number of moles of the given quantity, right? After that... you compare okay after that apply the unitary method after that apply unitary method apply unitary method to calculate the number of moles of this particular asked quantity moles asked okay moles of the asked quantity what is asked to you that is oxygen atoms and after this if they ask you the number of atoms here right right Now, once you know the moles, you can calculate anything. You can calculate atoms.
You can calculate molecules. You can calculate volume. You can calculate mass.
Right? Once you know the moles, you can calculate anything from here. Right? That is a very, very important thing.
Right? Okay? Let's apply this now.
I am going to apply the same thing with the... I'm going to apply the same thing here, same thing I'm going to apply this, okay? Firstly, I will calculate the, firstly, bacha, I will calculate the given moles, given moles of what is given to me, right?
Moles of, that is moles of HNO3, right? Firstly, I will calculate the moles of HNO3. That is, given mass is 126, molar mass is 63, that will be 2. moles, right?
Number of moles is 2, right? Number of moles is 2. Perfect. Number of moles is 2. Yes, ma'am. Okay.
Great, ma'am. Now, number of moles I have calculated for the given quantity. That is done.
This thing is done. Now, second is to find the number of moles with unitary method for that thing which is asked to me, right? So, what I will do?
They are asking the oxygen atoms, right? Now, you know. 1 mole, 1 mole or molecule is the same thing, right?
Okay, so or you can also write, you can also write 1 molecule, 1 molecule of HNO3 has 3 atoms, 3 mole of atom, 3 mole of atom. So, simply write mole only, why to you know increase the headache here, right? Okay. 1 mole of HNO3, right?
In 1 molecule, you have 3 atoms, right? That means in 1 mole of HNO3, you will have 3 moles of oxygen atoms, right? So, how many moles you have?
This is a general statement. In applying the unitary method, you always write the general statement. First after that, you write what is given to you. This is a general statement that for always 1 mole of HNO3, you have 3 moles of oxygen atoms, right? 3 moles of oxygen atoms always and always, right?
3 moles of oxygen atom. Now, for 2 moles of HNO3, you will have 6 mole of oxygen atom. 6 mole of oxygen atom, right?
That means number of moles of oxygen atom will be 6 moles, right? That is fixed to be 6 moles. Now, I have calculated the number of moles of oxygen atoms, right? I have calculated this thing also.
Now, I can calculate anything, anything. I will calculate all the things, atoms, molecules, volume, mass, right? So, firstly, Before calculating the molecules, let us, atoms calculate the moles, okay?
So, you know this formula that number of moles is equals to, if I am talking about atoms here, right? So, number of moles of oxygen, number of moles of oxygen atoms, oxygen atom it is, okay? So, yes, we can calculate it on the atoms, okay?
So, if students, we have calculated the number of moles of oxygen atom, right? If the number of moles of oxygen atoms are there, that means number of moles of oxygen atom equals to number of atoms, number of atoms divided by Avogadro's number, right? If students, I have calculated, for example, if I want to calculate the number of molecules of HNO3, then I know the number of moles of HNO3. Here it will be. number of moles of HNO3 equals to number of molecules of molecules of HNO3 divided by Avogadro's number because I am I have calculated the molecules I have calculated the moles for the molecule right here I have calculated the moles for an atom right that means here the here the formula will be number of atoms divided by this that means number of oxygen atoms That is number of oxygen atom that is going to be number of moles of oxygen multiplied by Avogadro's number.
That is 6 into 6.022 into 10 is equal to 23 oxygen atoms. Right? Okay, bicha?
Yes. Yes, haan. 6N.
Right? Just write 6N. Now, let us calculate all the other things also. What about, what about, what about volume? You know, number of moles of oxygen atom equals to volume of oxygen divided by molar volume.
So, that will be, volume is going to be number of moles multiplied by 22.4, that is going to be 6 into 22.4 liters, right? Okay, what about mass? Number of oxygen atom equals to mass divided by molar mass of oxygen is 16. So that will be mass of oxygen will be NO multiplied by 16. That is 6 into 16 grams. Right?
Okay? So you can calculate anything from here. Right?
Okay, bicha? Now let us come to second question here. Now you can see similarly same kind of question this is.
Same type of question, okay? Same type of question. Same type of question. Mass of H2SO4, okay? Mass of H2SO4.
This is asked to us. What mass? That means this is what they are asking, right?
This is what is given to you. This is what is given to you. So, don't use that much of brain here, okay?
So, what is our trick? What is our trick? what is given to you right here what is asked to you right here right then just calculate the number of moles of what is asked to you what is given to you what is given to you oxygen atom is given to you so number of moles of oxygen atom you will calculate that will be number of atoms that is 2na divided by Avogadro's number that is 2 moles okay answer is 2 moles right? Oxygen atom, the number of moles of oxygen atom is 2 moles.
Now, apply the unitary method here, right? Apply the unitary method. So we will write there are four oxygen four oxygen atoms four oxygen atoms in one mole of one mole of H2SO4 or you can write four moles of oxygen atom four mole of four mole of oxygen atom. If in one molecule of H2SO4 you have four atoms of oxygen That means in 1 mole of H2SO4 you will have 4 mole of oxygen atoms, right?
So that is why I have written the opposite here because we need to calculate the number of moles of H2SO4, right? We need to calculate the number of moles of H2SO4. So we will write the answer of number of moles of oxygen atom is 2. So we will write 1 mole of oxygen atom is 1 by 2 mole of this, right? 1 by 4 mole of this, right? So...
2 mole of oxygen atom will be 1 by 4 multiplied by 2 that means that means number of moles of H2SO4 is going to be number of moles is going to be 1 by 2 that is 0.5 moles that is 0.5 moles right. So now we have calculated the number of moles here right. Now second part is also done given is done oxygen this is done Now, the third very important part, that is, if you have calculated what is asked to you.
Now, they are asking the mass. Okay, we can calculate mass of H2SO4 will be beta. Number of moles multiplied by the molar mass, that is 98. That is in grams.
Answer will be in grams. Right? What is the volume of H2SO4?
No worries. That will be number of moles multiplied by molar volume. Right?
That is in liters. Right? What is the mass?
We have calculated. What is the volume? We have calculated.
How many molecules? Molecule of. Molecule of. S2SO4.
That will be 0.5 into Avogadro's number. Right? 0.5 into Avogadro's number. Right, child? Any problem till here?
Any problem, this is the best method to apply mole concept, right? Best method. Now, next part is, I think, yeah. So, this is the number of electrons. This is the number of electrons.
So, here what we are going to do? Number of electrons in 19 gram of PO43 negative, right? So, firstly, calculate the number of moles. Firstly, calculate that this is your homework, okay?
This is your homework. I will tell you how to do it, okay? I'll tell you how to do it. Last time all of you did your homework. That was great.
Excellent. Right. So now let us see the number of moles of PO4 3 negative. Right. First we calculate that.
That will be 19 divided by the molar mass of PO4 3 negative. That is 31 into 64. That is 95. Okay. That is 95. Right. This is going to be your number of moles of number of moles of PO43 negative, right?
How many electrons? How many electrons? Number of electrons in one mole, in one mole, that is going to be beta.
Number of electrons in one mole, 15, that is the atomic number of phosphorus, right? 15 plus atomic number of oxygen is 8, right? 8 into 4, right? 8 into 4 plus. It has gained 3 electrons.
Right? Right, beta? So, what is going to be the answer here? What is going to be the answer, everyone? What is going to be the answer?
Right? It is going to be 15, 35, 0, 90. Sorry, 15. Wait, wait, wait. That is, should not be 50. Yeah, okay, okay.
47 was for PO4 and 3 negative it has gained. So that will be 50 only. Yeah, so it will be 50 only. yeah okay so electron is 50 right so if we talk about in one mole you have these many electrons and number of moles are this so number of electrons number of electrons will be number of electrons in 19 gram of PO43 negative is going to be 50 into 19 by 95 electrons right homework to care have solid myself right Okay, I have solved it myself only. That is also done.
Now students, the next part is stoichiometry. Right? That is stoichiometry.
Stoichiometry means when you are comparing the values. But here you will also apply the same method. The same method given as then calculate the number of moles. Then unitary method. Then calculate the number of moles which is asked to you.
Same method you will apply. But here students, I am not talking about one molecule. Here I will be talking about one reaction, okay? Here we will be talking about one particular reaction that is a balanced reaction, okay?
Here we will talk about a reaction, okay? Here you will always see a reaction and you will balance it firstly, then you will apply all the other things, right? This is not a theoretical concept, so we will do it with the help of a question. The question students here is, The question everyone, the question here is how many grams of CO2 will be formed on heating 33.6 gram of MgCO3, right? So firstly what I told you, you need to know the reaction here.
The reaction is MgCO3 on thermal decomposition give MgO plus CO2, right? That is the thermal decomposition, right? After this, is this a balanced equation? Yes. This is the balanced equation.
1 mg, 1 mg, 3 oxygen, 3 oxygen. And you have 1 carbon, 1 carbon. So it is a balanced chemical equation.
Now the second step was what is given to you, right? Same thing you will apply that you applied in mole concept. What is given to you? What is given to you, beta? How many grams?
This they are asking. This they are asking, right? What is given to you?
This is given to you. Information about this is given to you. So simply what you will do?
What you will do? Given, calculate the number of moles of given. Then apply the unitary method. Apply the unitary method.
Apply the unitary method to calculate the number of moles of what is asked to you. Then you can calculate anything from here that is mass or volume or the particles right whatever they ask you or I would say molecules right okay the same thing I am going to apply here just copy this just copy this I am going to solve this for you here right okay so now so Let us calculate the number of moles of MgCO3 firstly. Let us calculate the number of moles of MgCO3. Right? Number of moles of MgCO3 students, that is going to be 33.6.
What is the molar mass of MgCO3, bacha? What is the molar mass? 24, that is the Mg, Mg plus 24 plus 12 plus there is 48, that is going to be 14. 2, 3, 4, 8, 84, yeah, 84 it is coming out to be, right, 24, 48 plus 24 plus 12, 4, 5, 6, 8, 12, 13, 14, 4, 5, 6, 7, 8, 84 only it is coming out to be, right, so these are the number of moles of MgCO3.
1 mg CO3 is going to give 1 in the balanced chemical equation. 1 mg CO3 gives 1 CO2. So the number of moles of CO2 will also be, right?
You will write 1 mg, 1 mg CO3 gives 1 CO2. So number of moles of CO2 will also be 33.6 divided by 84, right? That is going to be same here.
Now after that students what we are going to apply here number of moles of CO3 also we have put here right. So basically we have calculated for given then we compared it with the help of unitary method that in balanced reaction one mole gives one mole. So number of moles of CO2 is going to be same here right. So they are asking you the grams here. So what you will do number of moles of CO2, mass of CO2 right.
then molar mass of co2 that is 44 right and this is 33.6 divided by 84 and this is a mass of co2 you just need to calculate it here that is 33.6 divided by 84 multiplied by 44 Right? Okay? Just calculate it here, beta.
Just calculate it here. That is 33.6 divided by 84. Then it is multiplied by 44. For me, it is coming out to be 17.6. Okay? That, beta, you can also do on your own.
Right? These are the simple multiplications. Okay?
The chemistry I have told you how to do the mathematics part and the calculation part, you can do it. Right? okay let's not waste our time doing that okay but you have to do that because you have to conclude the answer there right okay now next part students next part is this one yes peter i think that is done same only right okay now the right option for the mass of co2 very very important question that is neat 2023 question The right option for the mass of CO2 produced by heating 20 gram of 20% pure limestone. Right?
Okay. So now, this is the equation that is given to you. Is this the balanced chemical equation?
Yes ma'am, this is the balanced chemical equation. First thing done. Balanced chemical equation we have sorted. Right? Okay.
Next part is the right option for the mass of CO2. asking you the mass of CO2 that means this is being asked to us right now what is given to us by heating this is pure limestone that means this is given to us right now this is a very important thing that they are not directly giving you the mass okay they are not directly giving you the mass they are saying either they are not directly giving you the moles they are saying by heating 20 gram of 20% pure limestone right So that means the mass of calcium carbonate that is limestone is going to be 20 gram of 20%. That means it will be 20% of 20 gram that is going to be 20 by 100 multiplied by 20. This will be cancel out answer will be 4 gram because only pure limestone.
Okay, the impure limestone is not going to react here. They will say only pure limestone is going to react. Okay. So by hitting 20 in this of pure limestone.
Okay. You have to calculate the pure limestone that is 4 gram that is going to react here. Right. Okay.
Now number of moles of CaCO3 is going to be mass of CaCO3 divided by molar mass of CaCO3. Right bacha, molar mass of CaCO3 is 100 grams, that is 40 plus 12 plus 48, that comes out to be 100, right? Okay, so here you can write here that this is 100, right?
This is 4, so just this will be 2 by 50 or 1 by 25, right? 1 by 25, right? Okay, or you can just simply write 0.04.
right, just simply write 0.04, okay, right, so now after that they are asking for CO2, right, so number of moles of CO2 we require, so what we will say 1 CaCO3 gives off 1 CO2, right, that means 0.04 CaCO3 will give 0.04 mole of CO2 right ok simple right so number of moles of CO2 is going to be 0.04 right now they are asking you the mass here so mass will be mass will be mass will be mass of CO2 divided by molar mass of CO2 that is going to be mass of CO2 is going to be number of moles that is 0.04 multiplied by 44 That is going to be your answer. 44 into 4, that is 16. 8, 96, right? 1, 96 and it is 1.96 grams.
Right? Okay? 1.96 grams.
That is your answer for this one. Right? Okay, bicha?
Yes, beta? Chalo. Now, any problem in this question?
Any problem in this question, beta? Any problem in this question? Then tell me in the chat box so that we can move ahead with other topic.
Right? Done? Everybody?
If that is done, green hearts in the chat box for that, right? Green hearts in the chat box and let me just drink some water here. Yes, bicha. Everybody, the josh is still high, no? The josh should be high, right?
The josh should not go down here, right? Okay, the Josh should be high because we are doing the most most important chapter, right? A very very important chapter, a very very important topics here. Stoichiometry, mole concept, then we are going to do limiting reagent, empirical formula.
All these topics are very very important, right? Yes, beta. Now, let us see how to, what is basically limiting reagent, right? What is basically limiting?
reagent, right? Okay, let us understand this with the help of a burger. Okay, so many of you are already having dinner or something.
You're like, ma'am, we are already hungry. You are talking about dinner and all stuff, right? But yeah, I'm also hungry, you know, but still I'm talking about dinner and all stuff, right?
You too also can have your dinner side by side, you know, when you're listening to me, you can have your dinner. I'm gonna have dinner like, okay, I'm eating and then teaching you. Not possible, right? Okay, so now students see.
You have 5 buns, right? You have 5 buns. You have 1, 2, 3, 4, 5, 6, 7, 8 cheese slices.
1, 2, 3, 4, 5, 6, 7. 7 cheese slices, 5 buns and you have 1, 2, 3, 4, 5, 6. 6 kebabs. Non-veg we are making, right? You have 6 kebabs, right?
I will say tikki. I will say simply tikki. Okay? Kebab or tikki.
Right, for vegetarians we will also have tikki or patty, right? In our menu, everything is there, okay? For people like me who are vegetarians, right? I don't want them to, you know, die hungry, right?
This has happened to me, Baswa sir and Shreya sir and Gopika ma'am. We went in a non-vegetarian restaurant. I thought, we firstly asked them, is there any vegetarian thing also?
They said, yes, yes, yes, we have. Okay? Then they just gave the non-vegetarian within 2-3 minutes.
And when it came to vegetarian, they took about 1 hour. Shreya sir, Baswa sir, Gopika ma'am were done with their lunch. But I was just sitting there and looking at them.
I was like, where is my lunch? And when everyone was like, okay, we are done. Then they were like, ma'am, this is your mushroom, crispy mushroom. What to do with this now? So this has happened to me.
Things only vegetarians can understand. So now students, these are 5 buns, right? Right? These are 5 buns and these are 7 slices. And for 1 burger, you need 2 buns.
You need 2 buns, right? You need better 2 buns. For 1 burger, you need 2 buns, right? In bun, we are just talking about bun, right? For 1 burger, you need 1 bun.
You need 1 kebab, right? And you need 1 slice. One slice. Okay. So, that means how many burgers we can form?
How many burgers we can form everybody? How many burgers can we form? We can form only 5 burgers here.
Because only buns are 5. Right. That means we can only form 5 burgers. Right.
5 burgers. That means out of this 1, 2, 3, 4, 5. 5 cheese slices we will use. But 2 cheese slices will be left. Right. 1, 2, 3, 4, 5, 5 buns we will use but 1 kebab or tikki will be left.
So the thing that is left that is 2 slices and 1 kebab is excess. Right? We are saying this is an excess. We don't have bun.
Right? We do not have bun. That is why we can't make a burger out of that. Right, you can just eat kebab like that but we can't make a burger out of that.
Right, we can only make 5 burgers. Right, so the thing that is completely consumed will be your limiting reagent. Right, will be your limiting reagent because we say because we do not have 6 buns, we do not have 7 buns that is why I can't make 6 or 7 burgers.
Right? That means I don't have these many, I don't have, I have the limitation of buns right that is why burgers are not formed so in the same way when we are reacting when there is reactants and products are being formed there is a limiting reagent that all that is always in limitation that we don't have excess of that thing right and the things that is completely consumed is the limiting reagent right that will be completely used up and other reactants which will be left in the reaction right as it is those will be your excess reagent. Those will be your excess reagent.
Right? Okay? Now students, let us do a question. Let us do a question based off that and understand that how to calculate it.
Right? Understand how to calculate it. Okay? This is in a reaction 4NH3 plus 5O2. In a reaction 4NH3 plus 5O2.
This is a reaction that is given to you. Firstly, always the step. to do this is the step to do this is always see balanced a chemical equation firstly balance the chemical equation firstly balance the chemical reaction second step students what you can do second step is to find the given moles given moles given moles in reaction given moles in reaction for all reactants for all the reactants right okay then you will find the stoichiometric coefficients stoichiometric stoichiometric coefficients are what that are in the reaction ok for example in this reaction the stoichiometric coefficient of NH3 is 4 for O2 it is 5 for NO it is 4 for H2O it is 6 that is in the balanced chemical reaction stoichiometric coefficient that is represented by S and this is represented by G right then you divide G by S then which is the smallest value The lower value, the lowest value is the limiting reagent. The lowest value is the limiting reagent.
Okay? That is the limiting reagent. Okay?
Now, let us see this. Let us see this particular reaction, beta. In a reaction, 4NH3 plus 5O2 give rise to 4NO plus 6H2O. Okay?
Right? Okay, that is given to us. Right?
So just write the equation here. 4 NH3 plus O2, give rise to, plus O2, 5 O2, 4 NO, 4 NO, 5 O2, 4 NO, plus 6 H2. Right?
Okay? Now is the important part. Then, 1 mole of ammonia. They are saying in the reaction, we are taking 1 mole of ammonia, 1 mole of oxygen.
Okay. So, given will be beta. Given that is represented by S will be. Given that is represented by S will be.
Everyone, that will be 1 and 1 for both of them. That is 1 and 1. Right? That is 1 and 1. Right? Now, what is stoichiometry? For ammonia, it is 4. For oxygen, it is 5. right okay now calculate the g by s value that is general science g by s value right g by s value you can learn it by Gopika ma'am is very smart Gopika ma'am smart Gopika ma'am smart ok Gopika ma'am smart ok so here we can say sweet also you can write Gopika ma'am is very sweet right so here it is 1 by 4 right 1 by 4 It is 1 by 5, right?
Okay, so which value is lower among them? Which value? This is more value, so this is going to be the lower value. Lower value.
And the lower value is the limiting reagent. Okay, beta? The lower value is the limiting reagent. So here we can say, what is the first thing is, they will ask you directly that which is the limiting reagent in this reaction. Okay, so by this method, you can calculate the limiting reagent.
And NH3 will be the excess reagent. So here we can write this much, this much. All of oxygen will be consumed because O2 is limiting reagent.
Right? Because O2 is limiting reagent. Right?
That is the first thing. Now, what if they ask you how much NO is produced? How much H2O is produced in the reaction?
So always remember this one more thing that is all the products. All the products depend on, depend on limiting reagent okay they depend on limiting reagent for example for example if they ask you the amount of NO produced here that will be that will be 5 mole of O2 gives 4 mole of NO okay first in the general balanced chemical equation in the general balanced equation what is written 5 mole of O2 is giving 4 mol of NO. In the general equation, it is written, right?
So, that is 5 mol of O2 gives, only compare the product that is asked to you with the limiting reagent, nothing else. 5 mol of O2 gives, 5 mol of O2 gives 4 mol of NO. 4 mol of, 4 mol of NO, right? 4 mol of NO, right?
So, what you will write here? Yes, Pitta. 5 mol of O2 gives 4 mol of NO. But in my question, in the limiting reagent, I am given with 1 mol.
I am given with only 1 mol of O2. So, if I am in the lab, they are giving me only 1 mol of O2. How much NO will be produced? That is dependent on the O2 because that is the limiting reagent.
How many burgers I am going to form? That depends on the buns, right? Because that was the limiting reagent. I had 5 buns, that is why 5 burgers were formed.
Because I had only limiting reagent was buns. Not the cheese slices. Not the kebabs. Right? So, here answer is going to be this.
So, that means 1 mole of O2 will give 4 by 5 mole of NO. So, number of moles of NO produced will be 4 by 5. Right? Now, if they ask you number of moles of NO will be 4 by 5. Can you calculate the volume of NO beta? That will be multiplied by molar volume. 4 by 5 multiplied by 22.4 liters.
Right? Can you also calculate the molecules of NO? Molecule of NO, that will be 4 by 5 multiplied by Avogadro's number, that is the molar particles, right? Can you calculate the mass of NO?
Mass of NO will be, that is 4 by 5, that is number of moles multiplied by beta, that will be multiplied by what? Multiplied by Everyone, mass of NO, molar mass of NO, that is nitrogen is 14, oxygen is 16, so that is going to be 30, right? So, that is going to be molar mass of NO, that is going to be 4 by 5 into 30, this is going to be mass, right? Everybody here, any problem here, any problem in this particular question, right? How to do limiting reagent?
How to solve the questions? I guess there should be no problem because we have done it in a very detailed manner. Right? Okay?
Similarly, you can calculate the number of moles of H2O also. Number of moles of H2O also. So, you will see 1 mole of, no, no, no, not 1 mole. In the question it is 5 mole of O2 gives 6 mole of H2O. Right?
5 mole of O2. 5 mole of O2. gives 6 mole of H2O right that means 1 mole of O2 will give 6 by 5 mole of water from here you can calculate anything mass volume number of molecules of water whatever they ask you right okay yes beta and why have we taken one because in the question it was given 1 mole of O2 right 1 mole of O2 that is one okay yes beta Next part, next question, this is from N.A.Vasthi.
Consider the reaction, bacha. Consider the reaction. Reaction is given to you.
That is 4A plus B plus 3C. Give rise to P plus 2Q. That is given to you.
The question is given to you. Right, bacha? The question is given to you.
The reaction is given to you. It is a balanced chemical equation. They are saying, starting with 6. Starting with 6 mole of A, right? That means given is 6 mole of A, 2 mole of B, right?
And 4 mole of C, 4 mole of C. What is the stoichiometry? Stoichiometry is...
4, this is 1 and this is 3, right? So just divide it, divide it, g by s is going to be beta, that is going to be 6 by 4, 2 by 1 and this is 4 by 3, right? 4 by 3. So 6 by 4 is 2, 3, 3 by 2, that is 1.5 only, right?
That is 1.5, this is 2. And what about 4 by 3? 4, 3, 3, 1, right? 3, 1, 0, right?
3, 1, 3, that is 1, then it is 0, 3, 3, 9, 1.3, right? That comes out to be 1.3, right? That comes out to be 1.3.
So here, as you can see the lowest value is, lowest value, I think you are not able to see this. Wait, wait, wait, I will just write it here. I will just write it here.
That is going to be students. That is going to be 1.5. This is going to be 2. This is going to be 1.3.
Right? So the lowest value is this. This is the lowest value.
This is the lowest value. That is the limiting reagent. Right?
That is the limiting reagent. Right? So we know that C is the limiting reagent in this question.
Right? Now what they are asking you? Starting with 6 moles of this and this, the product Q. After the reaction, Q they are saying, C is the limiting reagent, Q they are asking you, right?
Q they are asking you, C is the limiting reagent. So what you will say that 3 mole of C will give, in the balance equation, 3 mole of C gives 2 mole of Q. It gives 2 mole of, 2 mole of Q, right? 3 moles of C, 3 moles of C gives 2 moles of Q, right? Okay, now in the reaction, in the given reaction, how many moles of C are given to you?
How many 4 moles of C are given to you? So we will have to calculate in 4 moles how much amount is there. So 1 mole of C will have 2 by 3 mole of Q, right?
That means 4 mole of C will have 2 by 3 into 4 of Q, that is 8 by 3. Mole of Q. So, 8 by 3 is the correct answer. Students, what I did here?
What I did here? Firstly, I calculated the limiting reagent by writing given. That is given to me.
That is, here it is 6 mole, 2 mole, 4 mole. 6, 2, 4. What is in the stoichiometry? 4, 1 and 3. 4, 1, 3. Then I divided it. The lowest value.
that is 1.3 is the limiting reagent, right? Now, the product will always depend on the limiting reagent. So, that is why I compared these two that 3 mole of C gives 2 mole of Q. 3 mole of C gives 2 mole of Q.
But in the question, I have to calculate it for 4 moles because limiting reagent is only 4, right? For example, buns were only 5, right? That is why only 5 burgers are available to me, right?
So, This is 4. This is 4. So let us calculate it for 4 by applying the unitary method that is 8 by 3. So answer is going to be B. Right? Answer is going to be B.
Right, bicho? So answer is going to be B. Yes, bicha? Okay. Before going into that, anybody?
How to differentiate? Ma'am, how do we know? How you know that they are asking about the limiting reagent?
Ma'am, how can we know that this question we have to solve with the help of limiting reagent? Ma'am, all the questions seem to be same only. That is the biggest problem that students face in some basic concepts.
Right? So, how do we identify that? How to identify that? What you will do?
Simply one thing you will do. You will see if all the reactants is given to you. That means some...
kind of good word is there right some kind of good word is there that means here they are talking about limiting reagent firstly you have to calculate the limiting reagent in the stoichiometry questions now they will ask give you just two things okay in the stoichiometry see in the stoichiometry based question what will happen this is a stoichiometry based stoichiometry questions stoichiometry right by applying mole concept this is limiting reagent This is limiting reagent. So the difference that you are going to see here is, here they will give you one thing they will ask and one thing they will give. Right?
From given thing, from given thing you will find the asked thing here. That is the criteria of stoichiometry, right? But when it comes to limiting reagent, what they will do? They will talk about, give you all the, all the reactants, okay? All the reactants information, information for moles, information for moles, right?
They will give you number of moles directly. or they will give you the information of all the reactants so that you can calculate the moles for all the reactants. That means they are asking you the limiting reagent. Okay.
That will be solved with the help of limiting reagent. That is the difference of stoichiometry and limiting reagent and to identify that which method to apply. Right. Okay, bicha. Now, now, last part is empirical formula.
Last thing of today's empirical formula. Everybody. Smash the like button right now and share this with your friends.
Share this with your friends right now. And I want all of you to write, comment down, comment something. Like if you like the video, if you like the session, with all the hard work that we are putting here, right? That we also need, we are also humans, yeah?
We are also humans, right? That is, we also need appreciation from your side, right? You may feel like, okay, ma'am, maybe ma'am doesn't even see our comments.
Maybe. She is so like busy. Maybe she is not able to see her comments.
Even if I am too busy, right? Before I go to sleep, that is the thing. Before I go to sleep, I see your comments on my videos, right?
I see your comments. And that makes my day, right? That I feel so relaxed that okay, these students are liking the content.
That is why we ask you to comment down, right? So without even asking, you should comment down and also like the video, share to the other friends. right so that they can also get the knowledge that you already know what kind of content i am providing you in just two to two and two point five hours i am giving you a content of seven to eight hours with not even a single question that you might not see you will say okay not even a single question in today's lecture is like okay so easy they will not ask this in meet exam okay all the questions here are predictable questions for meet exam Right, so I have specially picked these questions from different different sites and I have picked this from TATVA PDFs, I have picked this questions from N Avasthi also, right and picked this questions from PBCL questions also. So that is how I have picked all these questions, right, you will see the screenshots of different different things, why? Because I have personally picked that for you, right, okay, so that you can get an idea of all the kind of questions that they ask you in your exam, right bacha, okay, very good, very good.
Very good. Now, let us see the empirical formula. Any idea about empirical formula, beta?
Any idea about empirical formula? Oh, God. Wait, Hmm, okay.
Yes, bicha. Thank you, bicha. Thank you. Chalo. Now, what is empirical formula?
That is, bicha, the simplest ratio. Let us understand. Let us understand with the help of an example. What happened?
Right? Let us understand this with the help of an example. For example, I am asking you that this is the formula of glucose, okay? That is C6H12O6.
That is the formula of glucose. Bhai sahab, what is happening to you? Is everything alright?
Okay? Are you fine? Good to go?
Shabash. Don't worry. We'll just make you free in just 30 minutes.
I think the board is also tired like... Diksha ma'am is not stopping only. Oh my god, some kind of atma or something is there, is it? That is very scary, right? So, Ghosti, this is Ghosti digital board.
Oh god, what is happening, dude? What is happening? What is happening to this board? It is literally blinking. Okay, relax.
I think what I should do, I should firstly save it. Right? I don't want it to go.
Oh my god something is happening here. Oh my god. Please Bhagwanji help me out. I don't want this PDF to go anywhere.
Guys something has happened here okay? I think the board is also tired. Let us see if it is working or not.
Last time I'm just saving it. I just wanted to get saved. Because I don't want to lose this PDF. Right? I want all of you to go through the notes.
Oh, successfully it is saved. Now we will just exit it and we will see that if it is working. I think the board is only having some issues.
Right? The board is only having some issues. Then we will refresh this. We will try.
We will try our best. Again it is blinking, dear. Again it is blinking. I don't know what has happened.
So guys, we will just wait for two minutes. Right? Anything you want to say to this board? Anything?
Anything? All are laughing here. What is happening, we don't know. Even I have no idea what is happening here. Right?
Okay, let us refresh it, okay? I think it is not going to work. Wait. Let's chit-chat, ma'am.
They're like, ma'am, okay, let the board be there. Okay, let's chit chat. Just give me two minutes, beta.
I need to see that what is exactly happening to this board. Okay? I think the board is totally lost. The board is feeling very sleepy. So, I need to talk to IT team about it.
Can you see? This is actually the color is also different here. Okay? One last try because Diksha ma'am never gives up.
I will give it one last try. Okay. I will give it one last try. Okay. I think now it is working.
I think so now it is not working again. Okay. No issues board.
No issues. We will, we will, you know, summarize the class now. Right. I will not teach you ahead because the board is not in the mood. Right, the board is like, okay, I am tired, right, please free the students as well.
Who, who out of you have prayed for this? I think some of you, some student from this chat only has prayed for that. Please, please, please, ma'am, please, please, we are tired, ma'am, I need to eat something, ma'am, I want dinner, ma'am.
Okay, that is why the board is behaving like that. Otherwise, this board is very loyal to me, otherwise it never behaved like this, okay. This board is so loyal to me, it can even.
even if there is no power there is no power on anything this board is there for like five to six hours the board will be working working working even if this board is totally heated up right it will work it is so loyal to me right but now we can see it is not working so beta I have to go for that right so I have to go right okay okay so everyone please to our beautiful sweet sweet board Because of this board only you are able to understand everything otherwise everything will be in the air only. Right. So please everyone write God bless you to the board please.
To our beautiful board. God bless you. God bless you. God bless you.
Please give blessings to this board. Please give blessings to this board. Okay. Yes.
Everyone. Blessings to the board. Blessings to the digital board.
Yes ma'am. You will get recovered soon board. Okay, so I want to see your creativity here. I want to see your creativity here.
What you can, how, if bored is a living being, how will you talk to the bored right now? Right, how will you talk to the bored? Yes, no creativity. I'm just saying, okay, bored, no, don't worry. Don't worry.
Just don't close your eyes and just open it. Close your eyes and open, close eyes and open. Just relax.
I am giving you proper sleep now. You will relax for 10 to 15 hours only then after we will use you. Okay? Just relax.
Just relax. It's like crying. The board is crying.
Right? Oh my chubby board. Okay.
The board is very young to die. The board is very young to die, no? Don't worry. Don't worry. We have our IT team, the doctors of board.
Right? They will recover it. Right?
They will operate the board and recover the board. Right? Okay? Okay then, bacha.
Okay then, bacha. Bye-bye. Take care.
See you all in the next class. And yes, say bye to God and bye to board and write down your blessings to this board as well as how you liked this session because we are going to just one topic is left. That is empirical formula.
We are going to do that in the next session. Right? In the next session, we will do empirical formula, molecular formula, percentage purity, percentage yield, percentage composition. Then there is one concept that is POAC, that is principle of atom conservation. Then students, we will do concentration terms.
And one more thing that we are going to do is equivalent concept. So that is going to be a very good, interesting session. That is the next session.
Yes, bacha? Okay then bye-bye take care see you all in the next class bye-bye take care write down your comments here and share this with your friends you have to share this with your friends share this on your whatsapp share this on your telegram share this on your instagram also if you do that and if you share this on your instagram then you can tag me also right and my telegram channel is and our english official telegram channel is you with down to neat english where you can see all the updates regarding any class and all the quizzes that happen is there itself right and also students i am also teaching in dna batch right so classes are going on we have started structure of atom in the dna batch so if you still want to enroll there you can enroll it we i have just completed two lectures of dna batch that will be provided to you in the recording itself but now you can continue with that because not much table we what labels we have done now just mole concept and structure of atom mole concept you can do from here also and record it will be provided to you but don't be so late that you skip everything and you have so many backlogs that will be very difficult for you to recover yes okay then bicha bye bye take care see you all in the next session