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See, Here we are going to study
ionic equilibrium
and it has many parts like
ionic product of water, weak acid / weak base.
Strong acid/base, buffer solution, salt hydrolysis, amphoteric ions
various types of titration,and solubility products and its applications.
ok, it is a vast topic and ofcourse if not understood properly it is the toughest topic or if understand properly, perhaps it is easiest topic of a entire physical
You need not learn anything. Let us start with ionic product of water, I will give you few points here which are important
So first I will write it, then i will explain it, ionic product of water.
Now, listen, although I could not write all the points related to ionic products of water
here, I require still more place. So now let it be there. Let me first cover it, then
I will like other instalments of ten and carry this, first thing, where we talk ionic equilibrium,
we must remember that talking about the situation where ions are placed in water, whenever you
prepare any solution in water, the behaviour of that solution because that is prepared
in water is treated with aqueous properties and one of the aqueous property is
ionic product of water. So, we we should understand how the water behaves so the behaviour of water and its properly is actually explained through these points.
Before that I will also explain one thing. Suppose I am taking a liquid in the container.
Container holds the liquid and the liquid acquire the shape of that container.
If the container is having some wholes water will ooze out through that will flows through that or liquid will flow through that.
If a liquid is flat and not having enough height sorry. Container is flat not having enough height, it can't hold too much amount of water.
So we know that container is very important to understand the property of liquid. Now here, my meaning of container is not physical container. I am not talking about a glass,or a tumbler,or a cup or tank or bucket, no, its not like that.
Basically ionic product of water is a conceptual container.
It is a conceptual container which holds all concept in it.
I mean if we are talking about acid and bases, weak acid and base, buffer solution salt solutions whatever, whenever you are talking in ionic equilibrium anything, it is there in premises, it is there in the conceptual container of water
that means you are in the framework of water
So until you understand what is the Nature of water.
You can't understand what happens on acid in to water
Because there are two members. Most of times we forget that when we add acid into water,we think
that its acid which shows the behaviour. It is not the acid which shows the behaviour.Its the acid and water,they are joined,
their combined behaviour is what we observe.
we are adding some salt into water
we think that it's a property of salt that should appear there, but we forget that water is also there.
So, salt and water, the joined effort, that's what we see as the resultant, behaviour also solution.
So, it is very-very important to first know that what are limits of water, what are the capacities of water, what is behaviour of water
How actually water has its own chemical properties and chemical events.
When we compare them with these all situations.
So if we don't understand water, we will not understand anything.
So, first, we go for that OK, it is again I would to like to tell that,
water, behaviour of water is again something like that you are preparing for IIT
and a container of IIT having Physics, Chemistry, Mathematics, but just imagine that in IIT-JEE paper
you got some question from Zoology & Botany, what will happen
There will be big problem.
This exam will be cancelled and people are unanswerable
So what happen that container it is out of container, it is beyond the premises
It is beyond the definition of container. So ionic product of water something like that our syllabus of all these topics.
It covers that, it holds everything here that a strong acid will, see you here, a weak acid, see you here, everything is here, everything's take permission of water
You people getting it ? When in your higher classes you go instead of water
you will have other liquid, like ammonia, sulphur di-oxide, you can have other like formic acid, like acetic acid, so not only ionic product of water, you might have in future you probably
How to study ionic product of acetic acid, ionic product of liquid ammonia
Are you people getting it. So which container are you going to study
that is first needed, that's why I explain here.
Ionic product of water. Now, there are many things in these sentences
In order to start it, this first line is very important it's says that in water
we know that there are water molecules and these water molecules do move in random manners
They are continuously in motioned and we cann't defined a motion of specific particle with certainity
The particles is randomly moving. Second thing we know that although they are randomly moving but their speed are not the same
Few particles move very fast and few particles are dad slow, slowly they are moving
All particles move with different speeds
Third thing we know that particle moving very fast
always do not move very fast throughout it slights pans
It moves fast for a small period of time
then due to collision its energy is transferred in some other molecule and that start to move fast and that the first one slows down
So it is true that different molecules moved with different speeds but a specific molecule does not always moving with that speed
So speeds also varies
So Maxwell has discussed all these theories in a good deed & says that if we arrange them in their statics
in the statics where population is drawn against the energy acquired by them, a curve of this type is observed
Where as you know from left to right,
the energy increases and this we moves from the horizontally y dimensions, the population increases
We know that at this reach, the maximum population has the energy which is seems to be an average energy
This is an average energy
It is not too high not too low
of course some particles are there some slow and they are almost dead
They don't have the energy, but few particles are so high energetic, that their motion can't be imagined that how fast they are moving
OK, and this curve as a fixed area between this curve and this axeses
as you keep the temperature constant
If the temperature in thermometer
it is showing the specific values say right now supposeit is 20ºC. So if it is 20º this will not change, this is a fixed value wherever you are in India or Pakistan or you are in Japan, anywhere
Throughout the universe the distribution of the energy of water particles will be like this
OK, now let me tell you if, suppose I'm going to visualize, the collision of 2 particles to water molecules and both the water molecules are same this reason from 1 and 2
They are moving very slow, slow and slow
Collide it then it's starting moving here, nothing have happened
Collision could change only the directions. The bond does not broken
OK, something like that. I'm going very slowly on car 20 km per hour and another car also coming here with 20 km per hour, there was a collision and I got irritate it
I come out of the car and saw the car.
Nothing it has happened, so we shake hand. Hello, how are you
What is your Name ? and all that
We are luckily because nothing has happened today
OK, so this water molecule shake hand and move on, that's it
But imagine this water molecule, first water molecule, this one belong in this region
Incidently the second one also moving in this region. Move very fast like the young people drives the bykes and all that.
It is looking that no one faster them here
It is true that one is faster than here to go in the product side
They really want to go to the product very fast.
OK, so such two water molecules are coming moving very fast. As soon as they collide, what happens
a bond should be broken because collision transfers the energy. Molecules don't know what to do this energy
They can do 2 things. First they can increase their speed and the speed is already very high
Second with this extra energy, they can break there some extra bonds.
So this is water molecule moving very fast and heating to this water
This depends on the angle of the collision and the central of the mass of collision two molecules
It depends on number of things, but something will happen like that they transferred from one molecule to another and increase the energy molecules will lose a proton
Are you understood
Something like we that as you seen in movies there are sometime two cars are coming very fast and colliding and people sitting in them don't find them the shake hands
They directly move to products
Some finder them and I taught earlier the bumpers which we keep there front and bottom they will get through in random manner and observe the energy and all that.
We know what they were expecting the scenes there
Similarly when the water molecules attacks, having very high speed and very high speed if they are colliding
what happens the lone pair, it takes the hydrogen of one of the water and that becomes H3O+
See one of the lone pair not present here only one pair
usual ware has two lone pairs. see I am going to shade it so it can easily visualizes so there are two lone pairs after accepting proton it has only one lone pair.
and what then happen this bond is broken this pair of electron also become a lone pair so this OH has three lone pair this is called auto ionization of water
Its also called self-ionization. It is self explanative word why it is called self-ionization.
So, it is clear that two water molecules collide, some this reason is very important. I want to attention you're here. It is very important
I am talking about collision of only these water molecules, which lie in very high energy level, very high energy band
I can't say that all the water molecule which collide twin into a H3O+ & OH--. Understood ? So what is here idea
The thing that is a large number of water molecule exist in that from which is very high energy
no, its very small, very negligible amount of water molecules only moves like moving rockets. So what happen
only those molecules collide are enable enough to break the bonds and transfer the proton
All water molecules can't do that understood ? So, I were see the ionization, the feeble ionization is written here, we can write it H2O+, giving H3O+ & OH--.
I would like to mention I thing that when people write thing equation, this seems more logical but in a simpler form it can be written in this form also
That one water effectively dissociated into H+ and OH--
Here I would like to draw your attention here with specific problem
What is that it is be very attentive, here H+ ions, these H+ ions are not alone, they are actually in the vicinity of water molecules
So some water molecules can solved it and it by its lone pair. You know lone pairs are electron
So bonds happen into H+ ions. This lone pairs called a kind of hydrogen bond. Now, let getting other water a many waters
So these many water are actually forming a layer around in it
A layer around in it all around because of the attraction and this is called hydration of H ions
Now, what is important ? I have to explain you
You understood that what I did here. I first took H+ OK, then I brought one water and says that this water will form a hydrogen bond
Can you guess what a formula now ? H3O+ why
This positive charge of H+ is consumed that there is 3 hydrogens exist
Now just some thing that I say that instantly another water also approach and said that I will also attract that proton
So, we can't stop that OK you also attract like proton. So what happens
what did the formula them ? 1, 2, 3, 4, 5, H, 5, 2, O (H5O2+) and what is the charge
Still +1 because charge entity is only here the proton. Now, since it is water molecules
We can't not say only two water. It third water comes, what we can do
We have to accepted. Then the formula should I have at 7, O 3, + even if the 4th come. You and me, we cant have object that
What will the formula ? H9O4+. So one will be full is just thing that proton can move around in a sea of water molecules
Proton is immediately captured by water molecules. Understood ? It something like that we are saying that in a jungle
where too many lions, tigers are living and they are very hungry and I am crossing that jungle and coming here to teach you chemistry you will say that sorry Sir
we know that whenever coming here, he will very good breakfast for those people
It is not possible to say that I am living that jungle of tigers and lions
What they are waiting for some food and I would be good food for them. Understood
So what is proton ? Good food for water molecules
All these species there OK. What is the way, I'm writing still don't want to irritate
put the value of n here and write condensed form and all having here negative charge. OK
What I did here, H+ with H2O whole N, put a value of N. 0, 1, 2, 3, 4 and write the value of species.
So an e.g. can I ask you ? In water, which of the following are found ? H2O, obviously that is not the choice
In water, which of the following is found H+, OH--, H3O+, H9O4+. Now those student is saying that there is a, b, c
these two ions are not alone, they are actually hydrated.
These points are all over. These points are very important. Whenever these reactions is taking place it is endothermic reaction, its very important to explain, why it is endothermic
Can anybody could tell why ? Endo-thermic means those reactions which will take up the heat, which absorb the heat, to happen this reaction, heat is absorbing by the surrounding.
Now, a question is, why is heat supplied. A good bond is found here, the answer is that we are breaking a covalent bond, inturn of that we are forming a very weak hydrogen bond.
Cause of breaking covalent bond which goes into the system is something about 200 K Jule and the energy which is release by the formation of hydrogen we will say 1, 2, 3, 4 and the rate of 40 KJ.
it may be 40, sorry 10 kj, it may be 10, 20, 30....... If suppose I go by 6.
It is only 60 KJ at this is not fully hydrogen bond, because as there as covalent bond get forms, the chances of heat releases getting lesser & lesser
So what happened to break a covalent bond ? More energy flowing into the system suppose this is water,More energy flows into the system , then why such kind of formation and lesser energy out of the system
So what happen system retain some amount of extra heat, suppose, I send into a 200 KJ and I received only 30 KJ
So what happened. This the having 170 KJ retain with it. Understood
Should I repeat ? Now, let me know, I said that constant temperature. If temperature is constant what will you think that the energy continuously flowing in
OK, Now, listen I'm saying that temperature is constant
So do you think that the continuous flow of energy into the system, see heat flows when the different temperature
If I maintaining constant temp. do you think that continuous energy take place ? No... ........... If it is no
then the once the energy which consumes to break the bond, it is all said that done. After that nothing happens
Now, no more energy to flowing, because the temperature is constant. If no more energy is flowing, whatever number of molecules dissociated
they are still there in and that will be conserved, that will not change.
OK. If I increase the temperature, what would happen More heat will flow, then more water molecules will break. So you find increase the temperature this graph will change like this
that dotted lines, increase the temperature T2,this is T1.sorry this is T1 this is T2.
So what you find that at higher temperature, greater area represent greater frection of molecules which should under go the dissociation
Now, why ? What is the thermodynamic reason ? It's simple at higher temperature one more instalment of heat will flow into system that more extra instalment heat
will break few new molecules of water. That you will produce more H & OH ions these ions that the number of ions increase
So whether this thermodynamic approach or the mass well approach, the idea is the some, it will change therefore it was demanding, the constant temperature
OK, Now one very important point that hydrosonium ion is the entity responsible for acidic behaviour
Whenever we say something acidic, we must immediately stand that it is H positive. To make a sense I will just tell that you all in 9th class
You are taught, very strongly that H is an element. What is atomic number of hydrogen ? 1. How many proton does it has
1. How many neutrons ? It is only a atom which has no neutrons. 1 Proton
How many electron should have around it ? 1.
Now, just think, its one proton, 1 electron system. How that remove 1 electron. What is left ? The most energy positive charge
Why, It's said that didn't demanding 1 electron, didn't demanding anything in this world
That's wanted a single electron. You didn't allow me to have or electron with kept me. You snached that mine electron
Now, you face the heat and the strongest and the most dense positive charge of the universe. Understood
That the positive charge of the universe is the proton but when the proton was satisfied with a electron, it is hydrogen
So when we write H+ satisfied you must understand what is it ? It is a energy proton and energy proton like angry birds
They are ready to do anything, which we call acids. So you all see here acids
You will be afraid. Why ? Angry proton
You are afraid of not me, you are afraid of angry proton so, this the entity which is the basically causing acidity anywhere
In universe positive charge is acidity. Its another have the looking of the same concept which is study the Physics
That there are 2 terminals if battery, positive & negative. Positive terminal of battery as it is said, you are having H positive
It is as good as saying acid. So during physics you look OK
Understood ? Now, likewise if you have hydro-oxide ions, called base. This is the responsible of basic behaviors
OK I would like to tell that OH-- that means the negative terminal of battery that is means the base
Don't forget the ions system, in inverse we find 2 charges, positive & negative. In Chemistry, we call same charges positive & negative as acid & base.
Battery has 2 terminals acidic terminal, basic terminal OK, come on. This is another important discussion. After studying all this, we are at 1 very conclusing point
Here it is that out of the bulk water, only few water molecule dissociated
It something like the behaviour of the acidic acid. Which we studied in this chapter. At acidic acid dissociate feeble to produce acetate ions & protons
Do you remember that only 2% to 5% maximum 5%. 2 to 4% dissociation confirms that it is a weak acid. So here it's not 2% not 4% even less than 1%. Its very poor dissociation.
I will not hesitate to say that dissociation is actually a type of weak acid dissociation. Understood
If it is like a weak acid dissociation, it gives & encourage me to write an expression as we use to do for weak acids
How ? This is water equilibrium. With this equilibrium, If I write the value of K. It should be produced active masses divided by reactant that is water active masses
I had written it. Now this is the place where has asked different many questions
First thing, many people get confused by KA, because the book everywhere KA is 10--14, but I didn't here that I had written 1.8 × 10--16,
because I'm not writing ionic product of water. I am saying that water is like weak acid
If you write weak acid, write benzoic acid 1.8 × 10--16 and sorry for acetic acid we write 1.8 x 10--5 as we have written it acetic acid
we write for water also values 1.8 × 10--16 for phenol we write 10--10, for alcohol we write 10--14. We have written this values consistently
Understood ? Now, this the first thing where students may leave this value. This value could be obtain experimentally.
How could be experimentally just before 3 and 2 days. I told conductomatic titrations. I'm not describe here
but conductomatic titrations when conducts it. It can tell me the value of conductivity CAPAA
from CAPA by dividing can see that I get the molar conductivity
I know this molar conductivity. Conductivity at C on infinity. It give with alpha.
Once I know alpha I multiplying this alpha. As K = C alpha 2, I can get to the value of K. So its not very surprising to write this K
So it can obtain experimentally. Understood ? So I you pluged this value here, I have rewritten this expression
This K value which is the obtain by conduct ionic titration is plugged here. Will you remember
Second thing water concentrations, Now which is the place, where 95% will students fail to put the correct value, that's why
it is asked in IIT-JEE in 2008-09. I just having a slip of it. About 2008
it is asked in IIT-JEE in 2008-09. I just having a slip of it. About 2008
Well, it is asked that the molar concentration of water you know 99% student will Write 1
because in chemically equilibrium water means 1. So its molarity are put 1.
There I very specially told you that was not molarity that was the activity of water
I am going to activity of water it would have been 1 am I writing the activity here
NO it the molarity so lets see what is how to calculate the molarity we all know that the molarity is moles divided by volume
let we assume 1 liter water every knows that density of ware 1 gram per ml near about
not very praises but for our study purpose it is sufficient 1 gram per ml so 1 liter of water is 1000 ml water so it is 1000 gram of water
1000 gram of water divided by the water molecular wait that is 18 will gave me 55.53 it is a molarity what does it mean.it means that when you take 1 liter contenar. I am going to tell you a real sense of life
please try to follow this when ever you have 1 hand full of water. this size can hold only 18 gram of water
this is about 18 gms that one hand full of water. Then how many such hand full of water I have needed here
55.54 this was amount which here, everyone knows this. Now if I plus this value and this value in this expression.
See, this expression, I placed value, multiply them, when you multiply you find at 18 × 5 = 90 and again 90. So its going to be 100
This multiplication is 100 and 100 is 10--16 forms 10--14.
Right side is left side with H & OH ions so you find that this multiplication is a simplified expression of the product of OH ions and OH ions
That is called 10--14 which is called ionic product of water. Understood
So, what does it say ? Please listen. Initially I said that the container ........... the capaicyt of container that it can hold H and OH ion in any number
The capacity doesn't allow the go beyond this value, when they are multiplied. OK, 1 very important thing H and OH ion should be essential to present in water
Take some water. Some people think that I am taking acid,only H ion should be there can I ask a question
How many people think that this is a HCl solution and OH ions are presents there
If I say probably some students go out of the class and say that this teacher doesn't do anything
He say that HCl here and OH ion in the solution. So you don't want to study here, you are a big fool
But remember, I'm telling still correct you are asking it then you are fool because there is no solution in universe which is mode up of water
Its divide of OH ions must have OH ions. If it is water, acidic water, basic water, salt water sea water, lemon water, lime water, say any kind of water.
Rain water, Tank water, any kind of water if you take that will have H2O and H ions and OH ions
So then answer is I am going to tell the answer is quantitatively its very important to go further
I can write 100% surety. You should also remember H ion will never be O & OH ion will never be O in water
It's for your confidence only. Then 1 thing when we understood at that H & OH ions are essentially present
then a question is asked what is the relation between this H & OH ions. It is here to draw a graph
So you find that a kind of hyperbolic curve is observes, why
What it is ? Because the product of these two is constant. Understood it ? What kind of curve you call
Rectangular hyperbola. It is rectangular hyperbola. Whenever you have x & y. Equal to constant
It is a rectangular hyperbola that for PV is constant.
It is similar curve. So this is what. Now the next important point OK if you understood this
we should know, what is the acidic solution & what is the basic solution ? What are all that
So before were jumping all that. I want to finish something that pKw. We call ionic product of water
It is only effected by 1 thing, that is temperature OK Whether you take acidic or basic solution, you take neutral solution
You take any kind solution, kW value will not change. It is always 10--14.
Why I said you whole drama is going in the container
That container size, container's limit are enclosed with the 10--14
Understood ? Suppose, I will tell you will answer one question I give you NH4Cl adding into water till the ionic product of water
I say that one more solution. In water. What is ionic product of water > 10--14
If I am taking NaCl adding water till that ionic product of water 10--14. If given that the condition is 25ºC
The room temperature then you will give this value
OK I have taken from water and I added acid, then I added base, then I added salt, even that I'm not happy
I added some organic molecules, and you are not satisfied and asking
The what is ionic product of water, 10--14. Don't change that, that is a container that holds everything will you remember this
Now, after this discussion a question comes that your are telling 25ºC. It is not necessary that have a water at 25ºC
Now in cold days, we have 10º water 9º water, 7º water then what is about this rule
The answer is that Kw value is changed. Kw the containers ability
It is changed when the temperature is changed because I have told you if you give more heat
more water dissociates will produce more H ions,more OH ions, more H & OH ions produced, will cause higher value of ionic product
So ionic product changes with increase temperature
So this value can be calculated by Kirchoff equation. This is Kirchoff equation. You getting my point
There are the 2 ionic product. OK at 2 different situations T1 & T2 and some people are surprised
& wondered by this delta H and delta H is equation which is telling water dissociated into H & OH ions
These equations delta H is supplied here the heat energy needed, which is added here to break the water is the delta H
So I will call this is the bond energy of water. Bond dissociation energy of water