So guys back to ionic libria weak acids I wrote a recap for you right and I hope you remember I said that weak acids are not a category, some acids will be stronger some will be weaker, I mean its K will be more, K will be less, K will be weaker So basically if this is a carboxylic acid right So basically, this is a carboxylic acid, so it depends on this bond, the acid strength. If the bond is weaker, then the acid is stronger and will dissociate faster. If the bond is stronger, then the acid is weaker and will break the bond less quickly and will dissociate less. Now to understand why the bond is weaker and stronger, we have studied two concepts, electron donors and withdrawers and delocalization. Right now I'm connecting these two concepts right with this concept.
So are you ready? So there we go So examples start cut there let's take an example Example let's say methanoic acid or ethanoic acid. Methanoic acid is also called as formic acid which I hope you remember it dissociates it gives you methanoate ion plus oxonium. So ethanoic acid and water it gives you ethyl newate iron plus oxonium So, according to the Bronsted and Lowry theory, I have defined the acids and bases. I will remember acids as proton donors and bases as proton acceptors.
Right, so, methanoic and ethanoic acids will act as water bases and in reverse, ions will act as acids and bases. So, Now let's see why methanoic acid is stronger than ethanoic acid. You know, the Ka value of methanoic acid is around 2.52 10H to the power of minus 5 and its Ka value is 1.51 10H to the power of minus 5. It seems that methanoic acid has more Ka which means that methanoic acid is a stronger acid than ethanoic acid.
And I think obviously you can see that OH bond, methanoic acid, The opposite of the word is weaker and the opposite of the word is stronger. It will be difficult to write this word. But we will explain how it is happening.
Okay. Now the explanation will go in two ways. Right? So you have to get my word now. Listen to this very carefully.
We basically... So we have to explain the phenomenon from reactant to product side and product to reactant side. So we will explain in two ways, reactant to product and product to reactant. So in either way you should write in the paper and then you score the marks. But remember the points explained in this scenario will remain same for all other scenarios but then only the examples will change.
the concept will remain same okay so see how I explain it so listen very carefully now please stay very attentive now very attentive Let's talk about the acid molecules first. Now, think about it. Hydrogen is neither donor nor withdraw. But this CH3 is electron donor.
Therefore, can I say that this is an electron donor. But hydrogen is nothing in methanoic acid. But don't forget that the OH bond is polar. And here oxygen is negative.
Hydrogen is positive. Oxygen negative, hydrogen positive. Oxygen electron is pulling from H.
It is pulling from H here too. Is it okay? Is it Now, in methanoic acid, Oxygen is pulling electrons from H Right? And this hydrogen is not saying anything It's saying do whatever you want So oxygen is pulling electrons from full strength It's polarizing the bond and weakening it But what is happening in this case?
Oxygen electron pulls, Methyl says don't pull. That electron is giving it. It says don't pull. It's not supporting it, it's anti-supporting it.
If there was an electron withdrawal here, I think it would have supported oxygen. But here, a donor is attached. When oxygen electron pulls, Methyl says don't pull.
Right? So what happens? Then this bond can't polarize as much, it can't be as weak as this bond was weak.
I think this becomes a point. So how do we write that? So we said, that kch3 is electron donor and creates positive inductive effect Making OH bond less polar. You don't get this in a market.
Right? This is what happened in terms of reactants. And with that, immediately I think, you will say that the OH bond in ethanoic acid is not a good bond.
is stronger than methanoic acid is that so so basically these two concepts are on the reactant molecule side now let's see the prod molecule side Are you seeing that since methyl is electron donor and hydrogen is not, then can I say that electron density will increase on the ethylenoid ion? On this ion, electron density will increase. Why? Because methyl is electron donor. When electron is donated, then electron density will increase on it.
Hygiene is neither donor nor withdraw, it's normal Although it's delocalised here and here So this is not a reason of difference It's similar in both, that's why I'm not talking about delocalisation Because delocalisation is happening here too PPI is happening here too, that's common I'm asking about the reason of difference So because of this I'm talking in terms of donating and withdrawing groups Right? Whatever So I think methyl is electron donor, hydrogen is none Right? Can I say that on ethinoate electron density increased? If electron density is being increased, can I say ethinoate is actually more negative than methanoate?
If it is more negative, then it will gain more age-positive wine. Therefore, it will act as a stronger base. So I think ethanoate will be a stronger base than methanoate because it's more negative. Or if it is a stronger base, then its conjugate acid should be weaker. Great.
So how do we say that? Like this. So we say that CH3 is electron donor. creating greater negative charge on ethnoate than methanoate. right so it will be a walk a up here I mean you can say that case ch3 co negative is a stronger base than methanoate right and fourth point which is code is moving with time you're at an away type basically can I say get it innovate is now less stable than methanoate okay so we can say that eth08 is actually I know a stronger base can I say it's also less stable because it's more negative it'll gain age possible more easily than Ethanoate.
It has one mark separate. We say Ethanoate is a less stable anion but please remember stronger acids, like stronger acids have more stable anions weaker acids have less stable anions right so fourth mark is that Ethanoate is less stable than methanoate. Right, so that's how you technically score four marks The ethanoate is less stable than methanoate But see me please the other can again saying you that stronger assets have more stable anions and weaker assets have less stable anions And that's a fact You get a good a weaker acid that those got anion will be a stronger base Because it'll be more negative go what negative would you use page possible easily tacker Degas? So always remember that stronger assets have more stable anions weaker assets have less tape Well, I know it's... Now I think in the name of these concepts we can say that in the homologous series of carboxylic acids, which is a homologous series of carboxylic acids, I have methanoic acid, then ethanoic acid, then followed by propanoic acid and the story continues.
Can I say that acid strength decreases? K decreases. Why?
Because the electron donor group is getting bigger and bigger. Larger the electron donor, so better the electron donor. Which makes OH bond stronger and stronger.
So I can say the OH bond becomes stronger. Now, let's conclude that methanoic acid is the strongest carboxylic acid among the homologous series. This is formic acid, by the way. Okay?
This is formic acid. And since nowadays, it's... You know like COV, nowadays COV ID is in the market in the environment and atmosphere. So I think that this formic acid, in fact formaline is formaldehyde, methanol, formic acid is made from methanol. So if you have a mixture of formic acid and formaline, right, so hands if, okay, if you wash your hands, It can be a good antiviral and antibacterial.
May Allah protect us. So, among all carboxylic acids, methanoic acid is the strongest carboxylic acid we have. Okay?
So, let's compare methanoic acid with benzoic acid now. Now, let's see what this is. Now, this is methanoic acid. and let's say this is benzoyl gas okay Now guys, everyone, so I think that's the concept, I won't write it, I'll just say it.
It'll be verbal only, but the conversation will be the same. I think that electron is pulling from here and from here as well. But the funny thing is that hydrogen is neither donor nor withdraw but in case of benzene it is a pi electron cloud inside.
I know it must have been delocalized. It must have done this too. But eventually because one bondway is another pi electron cloud, it delocalizes into the benzene ring.
So a withdrawing effect is created because electrons are rushing inside. for delocalization of the benzene ring. When electrons rush into the benzene ring for delocalization, this actually creates a withdrawing effect, which makes this OH bond weaker.
And this OH bond remains stronger. Please, I'm comparing. It's all comparative. Okay? So I think that the OH bond in benzoic acid becomes weaker due to which the acid becomes stronger Moreover, I think in case of this benzoate, I think electron cloud is completely delocalized The charge is completely spread, when the charge is completely spread, it means that the AH-positive ions will not be accepted here This means that it is a more stable anion, I think it is a weaker base Right?
Should I repeat? In Benzoic and Methanoic acid, I think that the delocalization in case of Benzoic acid Right it goes into the benzene ring for delocalization This creates a withdrawing effect making this OH bond weaker moreover in Benzoate again the charge is more spread It's more delocalized. It's stable.
It can't accept H-Posetamide more easily therefore It's a weaker base its acid is stronger And then of course you remember the stronger acids have more stable acids So Benzoate is a more stable anion than methanoate. Great? So guys, we're going to have more examples, right? Let's say if we talk about Benzoic Acid. So if we talk about this.
Let's say if I have Benzoic Acid. And I have, let's say. Chlorobenzoyl Casidol and let's say if I have 4-methylbenzoic acidol Let's ask a question And I will ask you which one is the strongest or weakest So I think that, what will you think?
That Cl is electron withdrawer Methyl is electron donor So I think Benzoic is nothing So can I say that Cl which is electron withdrawer So it becomes OH1 the weakest I think this should be strongest asset among all Can I say it has the greatest K value The smallest pK value But I think benzoic acid will be lesser and I think methyl benzoic will be the weakest. It will have the smallest K value. If we do it in ranking, then I can say this one is the strongest, this one is weaker and then 4-methylbenzoic acid is the weakest acid. Because electron donating groups reduce acidity, electron withdrawing groups increase acidity. So we can write the conclusion here that electron donating groups can negate the positive inductor effect.
Reduce acidity or electron withdrawing groups increase acidity. True. I think same concept goes on when I talk about some more acids let's say if I go in comparison to suppose connect a heiji mayor pass ethanol cassette or messy compare cartel with chloroethanol acid now I'm writing some examples right I will give you time to work on them so get ready please So there you go.
Please tell me which acid is stronger, which acid is weaker. You have two minutes. It starts now.
Okay, so ready? So I think that in my point of view. This will be stronger acid because electron is a withdrawal I think in ethanoic and propanoic, I think ethanoic is stronger acid because methyl is a smaller group.
It's a bigger group Although both are donors. I Think third example is fluoroethanoic and chloroethanoic. Fluoroethanoic will be actually The stronger one because it's a better withdrawal This is two chloropropanoic acid this is three chloro propanoic acid I hope you remember the acid carbon is always one when we name it and I think that K in case of two chloro propanoic acid see it is closer to the functional group it will have a better withdrawing effect than this therefore 2 chloropropanoic acid should be stronger why because CL is closer to the function group and will have a better withdrawing effect that's why 2 chloropropanoic acid seems to be stronger than 3 chloropropanoic acid but the fact remains saying electron withdrawing groups increase acidity electron donating groups reduce acidity let's move on Let's talk about ethanol and water. Ethanol.
Water. Let's talk about phenol. Phenol.
I'm writing very simplified dissociation equations. Okay? So everyone, I think that phenol should be the strongest one among all.
Let's say water is extended. What is happening in phenol? In phenol, the p electrons of oxygen when they are delocalized by pi electrons then the p electrons of benzene delocalize with the pi electrons of benzene it creates withdrawing effect.
It's pulling the electron from here and there and here and there When this withdrawing effect is created, this OH bond becomes the weakest And in my point of view, in this case of ethanol, since ethyl is the electron donor, this OH bond will be stronger Strongest among all Right, so I think that phenol becomes the strongest acid among ethanol and water. First of all, it creates a benzene withdrawing fat. Due to delocalization, OH bond has become weakest in phenol. Moreover, electron cloud is very much in phenoxide ion. I think it's the weakest base and I can't say it's the most stable anion.
Isn't it? Right? That's how we can say that those two phenomenons of delocalization and withdrawals and donors can be used to explain the strengths of assets It's actually a connection of ionic equilibria with organic Okay Again, I think yeah, I think you have a good thing worth discussing it You may be a little bit easy, but I think it's worth discussing actually Thinking I jump out cut them mono basic now.
I'm out of that league. I'm going into another concept Monobasic acid, it can be strong like HCL, it can be weak like HF because HF bond is too strong, it can be broken that easily. Monobasic acid is one that gives one H positive and one salt because anion is the salt of acid.
If we talk about dibasic acid, here dibasic acid is a very important acid. Because it can be strong too, like sulfuric. Vapra will first give 1H completely, giving hydrogen sulfate. But when it comes to hydrogen sulfate, it will be partial. Because hydrogen sulfate is a negative ion.
It will give positive ions with great difficulty. It will rather attract it. That's why it undergoes a partial dissociation.
But let's say sulfuric is strong. But in dibasic acid altogether, let's say if I talk about carbonic acid, it is a weak acid. Giving you H positive plus bicarbonate.
And then bicarbonate giving H positive and carbonate. But can I say that its Ka value will be greater and its Ka value will be lesser. Because carbonic acid is giving a molecule of H-positive ion In the next case, the bicarbonate ion is giving a negative ion of H-positive So to release the H-positive of the negative ion is a difficult process So I can say that every next dissociation becomes weaker I mean the Ka decreases but I can say that the P-Ka increases If we talk about tri-basic acid And please, if I talk about this, then it won't be K.
It will be K, because it is a weak acid of K. Weak acid of K values. It will be K.
Let's talk about tri-basic acid. Phosphoric acid. It is weak by nature. H positive plus H2PO4 negative one. Then H2PO4-1 gives you H positive plus HPO4-2 and HPO4-2 gives you H positive plus phosphate.
I think here and there I can say Ka decreases or I can say Pka increases because every time when negative i is given as h positive that becomes difficult is that so so guys so they were the mono basic acid die basic and try basic acids we had tego yeah let's move on now we know about weak acids how they are strong and weak right the K values and some facts about dissociation this was weak acids and now let's see weak bases of course weak base care which partially dissociates an aqua solution that partially dissociates in aqua solution Right? I think very famous examples can be aqua simonia or it can be amines. Let's talk about weak acids have k values and weak bases have kb values Basic dissociation constant If I talk about ammonia for example When we add ammonia to water it dissociates to give you Ammonium Plus or minus So the same thing will happen to casein Casein will be equal to Ammonium into OH negative divided by ammonia into water. And we know that water basically, its concentration remains fairly constant, there is no use in it. So if I take water up, right?
So I think that, what happens? It becomes K into water is equal to Ammonium into OH negative divided by ammonia. This K into water is called as K.
So I can say K is equal to ammonium ions into OH negative ions divided by ammonia. And can I say that Since we are talking about monoacetic bases So can I say that ammonium and OH-ions will always be in one ratio of 1 So can I say that K will be equal to Since these two are equal right These two are equal basically So we can say that ammonium ions and OH-ions are actually equal at equilibrium So if we make these two x square So K equals to x square over ammonia concentration And that's all. now what if I tell you the K value of ammonia let's say it is 1.47 10 is to power minus 5 to get x square over let's say many kaji game a ripass 0.1 mole per dm cube ammonia T let's say or 0.1 so I can find the value effects so it is 1.21 10H to power minus 3 mol per dm cube But these are hydroxidines Now I have to find H positive So I will use the formula KW is equal to H positive Into OH negative 110H to power minus 14 H positive I have to find OH is 1.2110H to power minus 3 So therefore H positive Will be equal to 8.2610H to power Minus 12 So now I have to find its pH So minus log 8.26 10 is to power minus 12 so I think minus log the answer is 11.08 is that so okay let's do a question calculate pH of 0.145, mole per team cube, methylamine, its PKB is 4.65. Start.
Okay everyone, so there we go. So basically I think that, I think this is your dissociation equation by the way. And the K of this will be CH3NH3+.
into OH negative divided by CH3 NH2 PKB will be equal to anti log minus PKB is it? anti log minus PKB that is 2.2410 raised to the power minus 5 2.2410 raised to the power minus 5 is equal to x square over methyl minus 0.145 into 0.145 under root it's 1.80 10 is to minus 3 Now that is the OH negative ion concentration. Now to get H positive from here, then KW is equal to H positive into OH negative. So 110 is to power minus 14 is equal to H positive into 1.8010 is to power minus 5. So H positive ion will be equal to 5.5510 is to power minus 12. therefore its pH will be equal to minus log 5.55 10 is to power minus 12 so I think it's minus log 11.25 is a pH did you get to know how the weak base is you know CalcTran goes was out to be is that so I'm just now weak assets key category may stronger weaker asset is the weak base category means stronger weaker base hoagie right let's see that too So we have a weak base category In which we will have a stronger base In which we will have a weaker base Stronger base will have more K, I mean PK will be less Weaker base will have less K PK will be more This explanation is easier It's actually easy to explain. Let's see.
This is ammonia. Its derivatives are amines. Let's say I have taken this.
Methylamine. It's a primary mine because it has two H's. If I take dimethylamine, it has one H.
Similarly, trimethylamine is also present. No age, all are alcohol groups All are aliphatic amines Now every N has a loan payer When we explained weak acid, we explained it in Bronsted theory Weak base we do in Lewis theory I hope you remember, what is Lewis base? Electron donor So in ammonia, there is no H in the donor So these electrons are readily available for donation Is that so?
So I think in case of ammonia there is no H but in primary mine there is one electron donor, in secondary there are two electron donors, in tertiary there are three electron donors. Isn't it? So...
in this phenomenon i can say in case of primary mine i think this is a better donor you know we will be a stronger base why because methyl electron donor is there okay so i think the electrons are more readily available for donation on nitrogen in case of secondary mine two electron donors are electrons are more readily available for donation right so we can say in these cases electrons are more readily available for donation Why because the Alcalgros Electron Donors? Yes, the Territory Mine should have been the strongest But the problem is that, well there is no syllabus here But you should know that the Territory Mine should have been a little stronger than all of them But it is slightly weaker than secondary mines But it is still stronger than primary Why is it slightly weaker than secondary? Because The alkyl groups that are present These non-polar groups They don't let tertiary mine dissolve in water Okay Just like that it becomes a weaker base further But that's generally a fact That aliphatic amines are Stronger bases than ammonia Right, so we can say that Ammonia has stronger bases than aliphatic amines And the reason for it to be a stronger base is because the alkyl groups electron donors and the electrons on nitrogen are more readily available for donation. But if we talk about its contrary, let's say phenylamine, I mean aromatic amine Now this is aromatic amine. So aromatic amine is actually a weaker base than ammonia.
Right, so aromatic amine where nitrogen is directly applied to the benzene it's a v-resonant monium why because its electrons will delocalize with the pi electrons of the benzene ring and they will be less readily built for donation so we say that that p electrons on nitrogen delocalize with pi electron of benzene therefore they are less readily built for donation Available for donation. Is that so? So, we can say that aromatic amine is less than pneumonia and pneumonia is less than elephatic amines.
Okay? So guys, so basically I think here the fact is that lecton donors increase base city Right? I think it's converse of acids And I think we can take an example further We can take actually further example And we can talk about the phenomenon That let's say if I have phenylamine Let's say I have 4-methylphenolamine and let's say I have 4-chlorophenolamine.
So I think this is an electron donor and this is a withdraw. So I think that 4-methylphenolamine will be the strongest base. I can say it has the highest K value. I think that Phenylalanamine will be the weaker base and 4-Chlorophenylalanamine will be the weakest base.
I can't say it has the smallest KV value. True. So electron donors increase basity and electron withdrawers reduce basity. So guys this was weak assets, weak bases, K, A and KV.
I hope you liked it and this was Happy Learning. Thank you.