So hello, my name is Abhishek and I welcome you all to our lovely and beautiful platform which is called JR College. So how are you all? I hope you all are doing great. Your studies must be going very well. So guys, as you all know, we have started the 12th chemistry batch on our channel.
Where you will be getting regularly 12th chemistry lectures. and all other remaining subjects All those lecture videos are available in our playlist section So if you want to study biology, chemistry, physics, maths, then do check our playlist There are lectures videos of every subject and every chapter I had taught you biology last year So keep watching all the other subjects Chemistry is coming regularly for you so keep your studies in a good gear because I have already told you that when you will reach the end of your semester then you will not get the chance to study there are many things that happen there like prelims, orals you have to write assignments, practicals so many things happen that you will not get time so from now on, study as much as you can and try to finish your syllabus as soon as possible ok? so let's start today's lecture as you know that we have started a very simple and very interesting lesson from the last few lectures it's name is ion equilibrium and 3 lectures of this are already uploaded on our channel so if you haven't watched it then definitely watch it ok?
definitely watch this video because if you start from the beginning then you will understand things better if you jump in between and watch this video directly then you may not understand things in a better way so watch things from the beginning and you will understand things better and your concept will be clear so in the last video, in the last topic we had studied Oswald dilution law we had completed Oswald dilution law for weak acid and weak base I have shown you many formulas in it so write those formulas in your books write it somewhere in the heading because when you solve many numericals then you will get those formulas I will also try to make a lecture video on numericals ok what are we going to study in this lecture today? today we will study Autoionization of water we will study about pH and pOH we will see their relationship so many things are going to be in this lecture today pH what is pOH and what is their relationship and then there is a scale of pH so today we will learn about all these things in detail so let's start today's lecture one more thing that if you have any doubt about the things that I have taught in chemistry and biology then you can come to my Instagram this is my Instagram ID, you can message me there Okay, that's fine. So let's start our today's topic that is our auto ionization of water and after that we will come to our pH and pOH. Let's start.
First of all, we have to understand what is auto ionization? Now you must be understanding a lot of things from the name itself. What is the name of it? Auto ionization. Ionization means dissociation.
When ions form, when ions are formed, then it is ionization. but here we have auto ionization what does auto mean? automatic what does auto mean? automatic means that you will not add any other reagent you will not add any acid or base still there will be ionization whose ionization will happen? water will be ionized so water itself does ionization this is called auto ionization of water what did i say?
did you understand? Ionization means that if a molecule breaks into smaller molecules, we call it ionization or dissociation same thing then, the water molecule is auto ionized, it starts breaking into smaller molecules we get to see its ionization that's why This topic is known as Auto Ionization Now see, I want to tell you one more thing It is not like you will mix water in water at home and it will get ionized It happens but in a very small amount In a very small amount So auto ionization happens in water but is very less in quantity you have to know this did you understand? so come on guys let's understand what is auto ionization first thing you have to write we are talking about water we are talking about water only ok?
so first thing you have to write write this statement that water ionizes in very very less quantity less amount you can write it like this what does it mean? this is also a weak word partial dissociation you can write as a to understand partial dissociation first of all, you are reading it partial dissociation you are reading it so what is the meaning of saying this? the meaning of saying this is the water is ionized, but it is very less so this is partial dissociation and if you are watching my previous videos, you already know that if you get partial dissociation anywhere then you will have to use this type of arrow I have already told you that if you do partial dissociation, then you will have to use this type of arrow understand?
Now let's see the reaction. What is happening in the reaction? What are the things that are causing the auto ionization of water?
Listen carefully. What your book is saying is that if you react H2O with H2O If you mix water in water, then it will have auto ionization. What will happen to it? Auto ionization.
Now I told you that it is not like you take a glass of water and mix it with another glass of water Now you will say that you can't see any ions in it Why is it happening? Why can't you see anything? Because this first line justifies it Water ionizes in very very less amount Very very less amount of ionization happens If the molecules of water interact And how do the molecules of water interact?
Through hydrogen bonding You know this, right? This is a very interesting concept Here H will be here and here. This is a water molecule. Similarly, here is one H and here is one H. So if you look carefully, this oxygen is more electronegative than this hydrogen.
So very slightly, a partial negative charge comes on this. Partial negative charge comes on this oxygen because this is more electronegative. If this is electronegative, if this is electronegative, So your hydrogen will be electropositive which means it will be charged positively on them Similarly, it will be charged on this one too This one is electronegative and this one is electropositive So if you see This one is negative and this one is positive So there will be a slight interaction between them This is a venerable interaction There will be a slight interaction between them too So because of this interaction These molecules break These molecules get ionized But in a very small amount So what is your book saying?
Now see, this H2O, let's say I write this H2O like this, HOH, this is the H2O, so nothing will happen, one H will go to this and you will have 2H left. From this H2O, one H will go here and you will have OH, OH-. So what will happen? What is left?
OH-. See, this is written as OH, so OH- is left and where did this H go? So, H3O2 is here.
Is it clear? Did you understand what happened here? Why did I put the sign of reversible here? Because it is partial dissociation.
There is very little dissociation. And you have to put this symbol in partial dissociation. What if there was complete dissociation? In complete dissociation, you will put a normal arrow. You find the rate constant there.
So here you... dissociation constant because here partial dissociation occurs we call this equilibrium constant so far you have understood things think and understand that you have understood things that auto ionization is water water is ionizing with its own molecules now you understand why it is called auto ionization because water with its own molecules It is doing ionization, dissociation, it broke by itself with its own molecules But this is very less, very less amount So, what did we find out? We found out that if we did its reaction, we will get one OH and one H3O. How did we get it? I have written it like this.
So, this H has gone to this, H3O plus. And this OH is left here, OH minus. Now, you have to write its constant.
Write it like this. You have to write its constant. What is its constant? Dissociation constant.
Okay, what is its constant? Dissociation. What is the value of constant?
I have told you. What is constant? Concentration of product divided by concentration of reactant.
So concentration of product divided by concentration of reactant. This is the formula. We have been following this since long. Now we can write here that what is our product? our product is this, so I will write it here on the side so k is equal to product which means H3O plus its concentration multiplied by OH negative its concentration divided by your reactant.
what is reactant? one H2O molecule is here, one H2O molecule is here, two H2O molecules are here so can I write like this? H2O and I have put square here what does square mean? two H2O molecules so what I did was I put square here.
it doesn't mean write one H2O then write H2O. what is H2O and H2O? what is 2x2?
it is 2 square so what happened here? it became square did you understand this? now this is a constant.
you got this as a constant now what will you do? you know this much Now what will you do? Now you will take this here.
See, see, this H2O square, the concentration of H2O square, what is this here? It is in divide. So if this is equal to this side, then what will happen in multiply? So K, wait a second, K into, what will happen?
Concentration of H2O square is equal to your H3. concentration of H3O plus and concentration of H. Did you understand? Are you clear or not? Have you understood or not?
Tell us. Tell us how but you are watching recorded. No problem.
I hope you understood. I haven't done anything. It's very simple. Take the value of K. This is your dissociation constant.
This K is your dissociation dissociation constant. Here dissociation is happening. Ok. Dissociation constant is what?
Product divided by reactant. So product is this. This is our product.
This is our product. And what is this guys? Reactant. This is our reactant. Clear?
So product upon reactant. I wrote H2O square twice, just this one. Now, let's move on.
Till where have we found? We have found, kids, constant into H2O's concentration, concentration of H2O square is equal to OH negative, then, write as we had written. H3O positive, concentration of H3O positive and concentration of OH negative. Is it clear? Have you understood the things till now?
It is very easy. Now if you look carefully, now if you look carefully, then in this condition, whatever is your water, whatever is the value of your water, that will remain the same. You know the value of water, that will remain the same throughout the reaction.
That will not change. So I can say, I can say, that the value of H2O is also constant. This will also be constant.
Because you know the volume of water. So, in this condition, you will write Here, the concentration of H2O is also constant. This is also your constant. So I will show this constant.
I will show this constant, children. K' from this constant. So how will this equation be?
This equation will be K multiplied by K' is equal to concentration of H3O positive and concentration of OH negative. Did you understand? I have not done anything.
I have just told you that the water molecule will also have constant concentration. So I took this constant as k' k' is the constant of concentration of H2O So instead of H2O, I have added k' Now you see, k is also a constant and k' is also a constant So instead of these two constants, can I write only one constant? Instead of these two constants, can I write only one constant? Yes, you can write So instead of this, I will write kW instead of this I will write kw now kw is also a constant value and what will be its value? concentration of P and H did you understand what I said?
did you understand what I said? it was very easy this is also a constant so from whom did I show this? from kw now there is a name for this kw This KW is a recognition of KW. So, write here.
Where KW is the ionic product of water. What is KW? KW is the ionic product of water.
And it is a concentration. It is your constant value. What is this?
Constant value. Along with that, this H3O positive, what is this? It is a concentration of hydronium ion.
Hydronium ion. So, this is your OH minus. What is this? This is your concentration of hydroxyl ion. Did you understand?
Did you understand? How much is it? This was your child's auto ionization of water.
After doing auto ionization of water, what do you get? You get KW is equal to KW is equal to this one. KW is equal to H3O positive concentration of H3O positive and concentration of which?
Is it clear? Did you understand? Now you should also know the definition of Kw. Read this definition after 2 minutes.
What have we found now? Kw means ionic product of water. Kw is equal to concentration of H3O positive and concentration of OH negative.
What is H3O positive? H3O positive is your hydronium ion and OH negative is your hydroxyl ion. So this is your hydronium ion and this is your hydroxyl ion. Now read this definition.
Now read this definition and you will understand everything. What is the definition? This is the definition of Kw, i.e. the definition of ionic product of water. What is the definition?
The product of a concentration of hydronium ion. What does product mean? Multiplication.
The product of the concentration of. Whose concentration is this multiplication? Whose concentration is this multiplication?
Concentration of hydronium ion What is hydronium ion? H3O positive So concentration of hydronium ion And the concentration of hydroxyl ion Of a pure water You need to write this And in which? At equilibrium condition Where did it go?
At equilibrium condition So the formula you have found Same definition You don't need to write this definition If you find this, then what can you write from this? You can write this definition. This is the definition. I found this value in front of you. I found this thing in front of you.
I derived this thing in front of you. And after that, I have written the definition. Same to same. Whatever is written here, that thing is in your definition.
That is ionic product of water. This is your ionic product of water. What is ionic product of water? Multiplication, kids. Multiplication.
What is the product? Concentration of hydronium ion. and concentration of hydroxyl ion in pure water and at equilibrium you will remember this because reaction in equilibrium is called as ionic product of Is it clear?
I hope you guys understood this much Now let's move on Now you guys have to know something else What did scientists do? Scientists did experiments Scientists do experiments It is their job to do experiments So scientists did experiments After experimenting, they found out that the concentration of H3O positive in pure water So what they found out was that after the experiment they found that the concentration of the hydronium ion That is 1 into 10 raised to minus 7 mol per liter. Okay. Mol per liter.
And the children who have studied lesson number 2 with me, those children know that this mol per liter is whose unit? This is the unit of molarity. Those who have not studied yet know that this is the unit of molarity.
What is molarity? I have told you the formula of molarity. Number of moles of solute divided by volume of the solution in liter. So, this is moles and liter.
So, when scientists did a lot of experiments, they found that the concentration of H3O positive, how much is its concentration? 1 into 10 raised to minus 7 moles per liter. Similarly, concentration of OH- is the same as 1x10-7 whole per second.
So, from here, I can find the value of Kw. Yes, I can do it. How will I do it?
See, what is the formula of Kw? Kw is equal to concentration of Hydronium ion and concentration of hydroxyl ion. How much value did I get?
I got 1 x 10 raised to minus 7 and multiply it by 1 x 10 raised to minus 7 So 1 will remain 1, 1 x 1 will remain 1 10 raised to minus 7, minus 7. How much will it be? 10 raised to minus 7 plus, so here it will be minus 7 minus minus plus will be done. So, what value will you get? You get Kw is equal to 1 into 10 raised to minus 14 moles per liter.
You have to remember this. Okay. Kw is equal to 1 into 10 raised to minus 14 moles per liter. See, it becomes minus minus plus.
This is what we studied in our childhood. We studied in 5th and 6th. So, here, kids, your end is this topic. Did you understand?
I hope you have understood these things So this is the auto ionization of your water Now next, we will jump into another topic that is our pH and pOH We will learn about pH and pOH What is pH and pOH? We have been learning since childhood that pH is that value pH is the value that tells us if something is acidic or basic Which is neutral and which is acidic We put it in the pH paper and then we get different solutions for pH If you put that solution in it, it changes the color And according to that color, you can also tell if it is acidic or basic Now we have to talk about what is pH pH means the potential of hydrogen atom Here also the potential of your hydroxyl atom. So if I talk about H, then remember its formula. Its formula is, kids, minus log to the base 10 of concentration of hydrogen.
Okay? Minus log to the base 10 of concentration of hydrogen. Meaning H plus.
H plus. Not just hydrogen. H plus hydrogen ion.
Understood? Okay? So, what can you write as the definition of this?
Its definition will be simple. That pH is defined as negative logarithm. See, this is negative logarithm. Don't forget this minus sign.
Right? So, you can write as it is defined as it is defined as negative logarithm to the base 10 of concentration of concentration of Hydrogen ion. This is Hydronium ion. You can write H plus ion also. No problem.
So this is your definition of pH. We will always remember the formula of pH. The formula of pH is minus logarithm to the log 10 Minus logarithm to the log 10 at the concentration of Did you understand? Did you understand? Okay Next come Yes Next we will talk about pOH Now what is pOH? pOH is also very simple One thing comes and the other also comes pOH What happens?
Listen This is the formula of pOH pOH is equal to minus log to the base 10 concentration of OH minus ion. Okay, concentration of OH minus ion. Means, you have to find out whose log is concentration of OH minus ion. So, you can make a very simple definition of this.
You can make a definition of this. What will be its definition? You can write.
It is a fine ass It is defined as negative logarithm of or you can write to the base 10 negative logarithm to the base 10 of of concentration of hydroxyl ion. Okay. The concentration of hydroxyl ion.
What is the negative logarithm of that? What is it called? It is called pOH. Okay. So, take a screenshot of this.
Then we will move on to our next topic. Next topic is Relationship between PH and POH This is very important topic Many times in exams, they ask that give the relationship or state the relationship between pH and pOH and then you have to solve it I remember when I was in 12th standard then this question came in my board paper also when I was giving the board exam then this question came in the same time state the relationship between pH and pOH so it is very important and I also solved it I will solve it here and tell you listen, listen it is very easy now we have read a formula of ionic product of water What was the ionic product of water? Kw is equal to Concentration of H3O positive H3O positive And OH negative If you look carefully, we have read this formula Now if you talk about H3O positive What will H3O positive donate? What is positive in it?
The positive is actually H+. What is the positive in this? H+. So instead of H3O positive, you can modify this equation and write TW is equal to H plus and OH minus.
I have written Q like this. This is H3O positive. H3O is positive. What is the work of positive? Donating.
When will it donate? If it has donated, it has one extra hydrogen. So, it has one extra hydrogen. That is why it has positive. So, I have removed H2O.
And I have made an equation for H+. This is your equation. This is your equation. That is Ionic. product of water water water water ok one more thing we had just found out some time ago that kW is equal to 1 into 10 raised to minus 14 should be 14 not 4 10 raised to minus 14 mol per liter we had also found this out ok We just found this value.
So, this is equation number 1. This is equation number 2. If you look carefully, then in both equations, KW, KW is common. That means KW is equal to this. KW is equal to this. KW is equal to this.
So, can I say, this whole term can be equal to this? Can I say, kids, this whole term can be equal to this? So, how will I write here?
I will write here, kids, that is, concentration of H plus and concentration of O minus is equal to 1 into 10 raised to minus 48. We will apply that later. Now you understand how this happened. Give this equation number 3. You will understand everything.
You will understand everything. If you listen carefully, you will understand everything. What did I say? See, we just found this KW.
What did we find for KW? H3O plus. H3O plus is positive. H plus is more. so we modified this equation for H+.
This is your equation. Then I found the same thing that is KW, the theoretical value that scientists got from experiments that is, KW is 1 into 10 raised to minus 14 mol per liter. If you look at the equation in front of you then KW is equal to this and KW is equal to this.
So from 1 and 2 you can write this equals to this. Now come to the second page. Let's solve the new page.
What did I write? The concentration of H plus and O minus is equal to 1 into 10 raised to minus 14. Okay. I am forgetting. I am forgetting to write 14. Okay.
Now, we have to take, what has he done? Multiply. This is your equation number 3. multiply log to the base 10 in equation means what you have to do is multiply equation 3 by log to the base 10 so what will be your value log to the base 10 and here what will be your concentration of H+, concentration of H- is equal to log to the base 10 of 1 into 10 raised to minus 14 now see this is in multiply you must have read log you must have read that if any sum is in multiply then if we take it in log then plus comes in between so if this is in multiply then what will happen here the equation will be log to the base 10 concentration of H plus plus here log to the base 10 concentration of OH, right Similarly, you can see here.
You must have read the formula. That is log to the base 10 of 10 raised to x. 10 raised to x. Whatever happens in 10 raised to x, what is its value? x.
If there is a minus here, then minus will be applied here. If there is a minus there, then minus will be applied here. There is no value of this 1. So log 10, log to the base 10. you have to find the value of 10 raised to minus 14 so what will be the value of 10 raised to minus 14?
we all know this formula you will know this formula in the future log to the base 10 raised to minus x so what is the value of 10 raised to minus x? it is minus x so i have written the same thing here 10 raised to minus 14 is not the value of 1 So 10 raised to minus 40, what will be its value? Minus 40. Did you understand the question? Now, you have to multiply. Now what you have to write is multiply the above equation, this equation, so give equation number 4. So you can write it like this, multiply equation 4 by minus 1. Now if you multiply this whole equation by minus 1, then what will happen?
If you multiply the whole equation with minus 1, then what will happen here? Minus log 10. H plus, this will also be minus log to the base 10, which negative is equal to, now see this was in minus from before, this will be plus, plus 14. We understood till here, we will write it again. What is this? Log to the base 10, H plus minus log to the base 10, which minus is equal to 14. Okay? Is equal to 14. Now we know, What does minus log to the base 10 H plus mean?
Minus log to the base 10 H plus means what? Where did it go? Look here. Minus log to the base 10 H plus means what? pH. And similarly, Minus log to the base 10 OH means what?
OH. So instead of these two, Listen carefully. Instead of these two, Look here. Minus log to the base 10, Minus log to the base 10, instead of this I can write pH. Right?
And minus log to the base 10, instead of this what will come? POH. And in between this will come plus symbol.
Why did plus symbol come? Because this minus is this. Right?
So, is equal to 14. This child got the value. You understood? You got this value. Is it clear? Is it clear?
Did you understand? So, this is the final equation. So, here you can write that if you add your pH and pH, then you get 14. This is the final step. Done. Let's move on.
Let's move to our next topic that is aqueous solution. We know a little bit about what aqueous solution is. So, let's know about this.
What are the things present in it? We will know in detail in the next class. Look.
There are three types of Aqua solution. First is Acidic solution. Second is Neutral solution.
and one is your basic solution. So, there are three types of aqueous solution in your book. Which are they?
There are only three. Which are they? One is your acidic solution, one is your neutral solution, and one is your basic solution. So, these are the three types of aqueous solution.
What happens? The pH value in this is always equal to pOH. Do you understand?
The pH value is equal to pOH. same same what happens in this? The value of pH in this is more as compared to pOH.
Okay? The value of pH in this is more as compared to pOH. That's why, your pH is smaller than your 7. What is the value of pOH? 1 x 10 raised to the power of minus 7? 1 x 10 raised to the power of minus 7, so you'll get log fog.
When you'll put the value of log fog, you'll get 7. So, you'll get something like this. Right? Do you understand?
Similarly, if you see here, the concentration of pH is higher than pOH. Then you get this derivation. Yes, correct.
And if you see in this condition, the value of pH is less as compared to pOH. Here pOH is higher. So in this condition, the pH is higher than 7. Here the value of pH is equal to 7. I have explained this to you in detail. We will discuss the rest in detail in the next lecture. So, that's all for this lecture.
I hope you have understood all the things I have taught you. Autoionization of water, what is pH, what is pOH, what are their relationships, whatever derivation I have taught you, you must have understood. Do write this in your book. Do practice this. The more you practice, the more things will be clear for you.
So do practice as much as you can, only then you will be clear about these things. On this, I have formulas are made, on those formulas also many numericals will be asked to you right kids, ok if you like this video then you will like the video if you are new to the channel then subscribe to the channel share this video to your friends spread this video to all your friends ok, so I will meet you guys in another video where we will talk about many more things till then take care of yourself and keep studying