TBR Gen Chem Chapter 4 Passage 3 #14

[JAH360]

The question goes: The acidity of halide-containing oxyacids increases directly with which of the following?
A. The increasing electronegativity of the halide.
B. The increasing bond length of the H-O bond.
C. The increasing size of the halide.
D. The increasing bond angle of H-O-X

So the answer is A, but couldn't it also be B? The stronger an acid is, the weaker the O-H bond, and thus the longer the O-H bond, right?

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[DrknoSDN]

I think acidity is based on the stability of the conjugate base. Therefore the bond length is not as important as having a more electronegative halide stabalize the molecule for hydrogen donation.

 

[Chrisz]

The halide is connected to O, which in turns connect to H. Through inductive effect, the halide can pull the electron density in the direction away from H. Therefore, Increasing electon increases acidity in oxyacids

 

[Chrisz]

Forgot to answer your OH bond length, O is always sp3 hybridized and H is always s-orbital in oxyacids, the bond length is always fixed

 

[Teleologist]

The halide is connected to O, which in turns connect to H. Through inductive effect, the halide can pull the electron density in the direction away from H. Therefore, Increasing electon increases acidity in oxyacids

So why is chloric acid weaker than nitric acid?

 

[Chrisz]

So why is chloric acid weaker than nitric acid?

Let me ask you a simple question, what is the charge on nitrogen?

 

[Teleologist]

Let me ask you a simple question, what is the charge on nitrogen?

Formal or partial charge? In what too?

 

[Chrisz]

Formal or partial charge? In what too?

Bro, Just draw out the lewis structure, you will find out why HNO3 has such a large acidity. You dont need to know whether it is formal or partial at this moment. Once you draw it out, it will be so obiious to you. Good luck. I know you can do it.

 

[Teleologist]

Bro, Just draw out the lewis structure, you will find out why HNO3 has such a large acidity. You dont need to know whether it is formal or partial at this moment. Once you draw it out, it will be so obiious to you. Good luck. I know you can do it.

I know it's acidic but I don't know if you actually read my original question: why is nitric acid stronger than chloric acid?

PS: I don't think you know.

 

[Chrisz]

I know it's acidic but I don't know if you actually read my original question: why is nitric acid stronger than chloric acid?

PS: I don't think you know.

Ok, i give out the answer to you, stop being a baby, be humble. N is positively charged with +1 when you draw the lewis structure. the halogens do not have a whole charge on it. You think which one has more tendency to draw electrons to it. that is why nitric acid is more acidic than chloric acid.

 

[Teleologist]

tendency to draw electrons to it.

Are you talking about Bronsted acidity or Lewis acidity?

 

[IslandStyle808]

Are you talking about Bronsted acidity or Lewis acidity?

Since it is a Bronsted acid it is also a Lewis acid, but he is trying to explain the increase in acidity. It seems like it has something to do with resonance (I am not sure on this one).

 

[Teleologist]

Since it is a Bronsted acid it is also a Lewis acid.

Damn, what a revelation. I was referring to the proton donating tendencies of nitric and chloric acid.

And don't go Googling either because the only relevant thing you'll find regarding this question via Google is a post that I MADE.

Chemistry is hard, brah.

 

[IslandStyle808]

Damn, what a revelation. I was referring to the proton donating tendencies of nitric and chloric acid.

And don't go Googling either because the only relevant thing you'll find regarding this question via Google is a post that I MADE.

Chemistry is hard, brah.

I will ask this are you wanting to understand or are you asking a loaded question? Chrisz answer previously pretty much describes most instances of why some oxyacids are stronger than others. Of course, there will be times when you need resources outside TBR to understand these chemical behaviors, which can be different from the defined concept.

I never said chemistry was not hard braddah.

 

[Teleologist]

I'm wanting to understand.

 

[IslandStyle808]

Okay I see. As I have said in the previous comment, I am uncertain. One would think that it has to do with the electronegativity in general (more lewis acidity), but I doubt this is the case. As you most likely know, the electronegativity for Cl is greater than N. I think what Chrisz is trying to explain is that since nitrogen is less electronegative than oxygen it is electron withdrawing. Thus it is pulling electron density toward it and stretching the H bond out, increasing the acidity in the process. With chloride, it is more electronegative than oxygen and it is electron donating. Thus the electron density is pushed toward the oxygen with the O-H bond. This decreases the length of the H bond and decreases the acidity.

I think this is the answer he was trying to give, if he could confirm it.

 

[pizza1994]

I think its cause in nitric acid the oxygen has a negative partial charge and the nitrogen has positive negative charge. So nitrogen will want electrons making it more acidic.

In chloric acid the oxygen has a positive partial charge and the Cl has a negative charge...so chlorine doesnt want the electrons cause it will be repelling....

this is how i think of it as to why chloric acid is weaker than nitric acid.....im not sure myself

 

[Chrisz]

I think its cause in nitric acid the oxygen has a negative partial charge and the nitrogen has positive negative charge. So nitrogen will want electrons making it more acidic.

In chloric acid the oxygen has a positive partial charge and the Cl has a negative charge...so chlorine doesnt want the electrons cause it will be repelling....

this is how i think of it as to why chloric acid is weaker than nitric acid.....im not sure myself

No disrespect, just to make something clear, cl have a partial positive charge instead of negative in this case. It is connected by three oxygens, oxygens are more electronegative, so cl has a partial positive charge, oxgyen negative. The partial positive on cl, and negative on oxygen can also be verified by drawing resonance.

 

[IslandStyle808]

No disrespect, just to make something clear, cl have a partial positive charge instead of negative in this case. It is connected by three oxygens, oxygens are more electronegative, so cl has a partial positive charge, oxgyen negative. The partial positive on cl, and negative on oxygen can also be verified by drawing resonance.

So the reason why HNO3 is more acidic than HClO3 is because the nitrogen is more electron withdrawing than chlorine.

 

[Chrisz]

So the reason why HNO3 is more acidic than HClO3 is because the nitrogen is more electron withdrawing than chlorine.

yes

 

[IslandStyle808]

yes

Awesome. Thank you.

 

[Teleologist]

No disrespect, just to make something clear, cl have a partial positive charge instead of negative in this case. It is connected by three oxygens, oxygens are more electronegative, so cl has a partial positive charge, oxgyen negative. The partial positive on cl, and negative on oxygen can also be verified by drawing resonance.

So the reason why HNO3 is more acidic than HClO3 is because the nitrogen is more electron withdrawing than chlorine.

EN of Cl: 3.16
EN of N: 3.04
EN of O: 3.44

What are you guys talking about? Positive charge on chlorine? Then why not nitrogen?

 

[IslandStyle808]

EN of Cl: 3.16
EN of N: 3.04
EN of O: 3.44

What are you guys talking about? Positive charge on chlorine? Then why not nitrogen?

They both have a positive partial charge, but nitrogen's is greater.

EDIT: This is due to the fact that they are both less electronegative than oxygen

 

[Teleologist]

They both have a positive partial charge, but nitrogen's is greater.

EDIT: This is due to the fact that they are both less electronegative than oxygen

So we chalk everything up to a difference in EN of 0.12 units? And so this greater positive charge on nitrogen makes nitric acid more acidic?

 

[IslandStyle808]

So we chalk everything up to a difference in EN of 0.12 units?

Yeah that's the reason.

 

[Chrisz]

So we chalk everything up to a difference in EN of 0.12 units? And so this greater positive charge on nitrogen makes nitric acid more acidic?

Think about the fact why I asked you to draw lewis structure for HNO3. It has a "whole" positive whole charge on Nitrogen by itself. When you draw lewis structure for HOClO2, it does not have a formal charge on it. Then why I say cl has a positive partial charge on it? Inductive effect. It is connected by oxygens. Oxygen have higher electronegativity than Cl. Then, Oxygen pull electron density away from chlorine. Chorine becomes partially positive.

 

[Teleologist]

Think about the fact why I asked you to draw lewis structure for HNO3. It has a "whole" positive whole charge on Nitrogen by itself. When you draw lewis structure for HOClO2, it does not have a formal charge on it. Then why I say cl has a positive partial charge on it? Inductive effect. It is connected by oxygens. Oxygen have higher electronegativity than Cl. Then, Oxygen pull electron density away from chlorine. Chorine becomes partially positive.

Both N and Cl are of basically equal electronegativities and there are three oxygens "pulling" on N and Cl.

What's the difference? The -I effect is equal for the N and Cl in HONO2 and HOClO2.

 

[Chrisz]

Both N and Cl are of basically equal electronegativities and there are three oxygens "pulling" on N and Cl.

What's the difference? The -I effect is equal for the N and Cl in HONO2 and HOClO2.

I think I have made the reason very clear throughout the entier discussion. The "LEWIS STRUCTURE" N has a WHOLE positive charge because it makes 4 bonds with the three oxygen atoms. That is why it make HNO3 especially acidic.

 

[Teleologist]

I think I have made the reason very clear throughout the entier discussion. The "LEWIS STRUCTURE" N has a WHOLE positive charge because it makes 4 bonds with the three oxygen atoms. That is why it make HNO3 especially acidic.

So you think that the O in H3O(+) has a whole positive charge?

 

[Chrisz]

So you think that the O in H3O(+) has a whole positive charge?

Bro, lets stop here, either you dont wanna accept someone's answer, just because accepting it is just equivalent as accepting as if he is smarter than you are, or you really need to work harder on Ochem. Besides these two reasons, I do not see any further reason that you keep asking irrelevant questions, besides proving that you are smarter and attempting to overwhelm someone you think smarter than who you are. If the first one is the case, I assure you that I am a normal person, not like a super genius as you are. The only reason I could give a reasonable explanation to why HNO3 is a way stronger acid than HOClO2 is that I studied hard and solved tons of questions when I took organic chem. In order to have a good sense and logic in Orgo, you need to do tons of questions and be willing to think outside of box but based on all you have learned from the textbook and solving problems. That is it, for this discussion.

 

[Teleologist]

But I drew out a hydronium ion and it had a plus on the oxygen!!! Same with ammonium ion, it had a plus on the nitrogen, so the highly electronegative hydrogens must have been stealing electrons from the nitrogen which makes ammonium ion such a strong acid since the hydrogens are so negative and the nitrogen so positive.

Thanks for clarifying. I'll just look for whole positive charges and obviously this will lead me in the right direction ! Thanks again brah were both gonna get 45s on the mcat.

 

[Chrisz]

But I drew out a hydronium ion and it had a plus on the oxygen!!! Same with ammonium ion, it had a plus on the nitrogen, so the highly electronegative hydrogens must have been stealing electrons from the nitrogen which makes ammonium ion such a strong acid since the hydrogens are so negative and the nitrogen so positive.

Thanks for clarifying. I'll just look for whole positive charges and obviously this will lead me in the right direction ! Thanks again brah were both gonna get 45s on the mcat.

Bro, sorry for the post above. I was being little bit harsh on you in the last post. I want to apologize for it. One more thing for clarification. It is not highly electronegative hydrogen stealing electron density from Nitrogen. It is the positive charge on nitrogen pulling electron density from hydrogen atoms that make ammonium more acidic than ammonia. Lets start with ammonia, the nitrogen has zero formal charge. Once it donates its electron pair to a proton, it gains a + charge, whcih makes it electron deficient, so it has a stronger pull on electrons from hydrogen atoms through inductive effect. This will in turn make hydrogen even more electron deficient than when it was in ammonia. The hydrogen are more prone to accept electron pair from electron donors. Remember, acid are electron accepters, and bases are electron donors. I really have to go back to my own studies. MCAT is coming up very soon.

 

[pizza1994]

No disrespect, just to make something clear, cl have a partial positive charge instead of negative in this case. It is connected by three oxygens, oxygens are more electronegative, so cl has a partial positive charge, oxgyen negative. The partial positive on cl, and negative on oxygen can also be verified by drawing resonance.

thanks. my bad...got caught up in the dang periodic trend without carefully thinking about oxygen and chlorine....

 

[pizza1994]

I dont know how you guys knew oxygen is more electronegative than chlorine actually.....if I wasnt provide the actual values then I would be like wtf no way to tell.....dang it

 

[pizza1994]

So the reason why HNO3 is more acidic than HClO3 is because the nitrogen is more electron withdrawing than chlorine.

this makes the most sense to me. I finally get this in terms of EWG........what an interesting question!!!!! love it

 

[Teleologist]

this makes the most sense to me. I finally get this in terms of EWG........what an interesting question!!!!! love it

The N isn't any more electron withdrawing than the Cl; they have essentially equal electronegativities. Using formal charges to determine that the N is electron withdrawing is like taking the movie The Polar Express seriously and trying to find the train that goes to Santa Claus.

1) H3O+. Positive formal charge on the oxygen. Do you really think that the oxygen is positively charged in hydronium ion?

So now we've destroyed the idea that formal charges can actually predict the real charge on an atom, here's the real reason nitric acid is stronger than chloric acid: resonance. And solvation entropy.

If it hurts too much to take it from me, take it from a MIT grad:

If you use formal charge to determine electron densities you will get screwed over on a regular basis.

So the reason why HNO3 is more acidic than HClO3 is because the nitrogen is more electron withdrawing than chlorine.

 

[IslandStyle808]

So now we've destroyed the idea that formal charges can actually predict the real charge on an atom, here's the real reason nitric acid is stronger than chloric acid: resonance. And solvation entropy.

LOL you are taking this too seriously. The only two explanations I could think of at the time were the differences in the electronegativities and the resonance. The electronegativities was the most significant thing I could think of as different at the time, but you do realize that I was trying to confirm this right? I also knew that chloric acid has one more pie bond than nitric acid, but how does the resonance work in this case (I know this is most likely the reason but can't figure out why)? I would love to hear an explanation of why resonance and solvation entropy accounts for this difference.

 

[Chrisz]

I'm wanting to understand.

The N isn't any more electron withdrawing than the Cl; they have essentially equal electronegativities. Using formal charges to determine that the N is electron withdrawing is like taking the movie The Polar Express seriously and trying to find the train that goes to Santa Claus.

1) H3O+. Positive formal charge on the oxygen. Do you really think that the oxygen is positively charged in hydronium ion?

So now we've destroyed the idea that formal charges can actually predict the real charge on an atom, here's the real reason nitric acid is stronger than chloric acid: resonance. And solvation entropy.

If it hurts too much to take it from me, take it from a MIT grad:

Bro, this is the last time I am going to explain this one more time. Read my reasoning carefully. Actually your electron density distribution does not have any contradiction with it. Electron density distribution is the final graph after electrons redistribution. Using formal charge is a way to predict how the electron density will redistribute after the oxygen of H2O donates a pair of electron to H+. Since the oxygen has donated a pair of electron to form a sigma bond with the proton, the oxygen becomes more electron deficient. Nobody likes to become electron deficient, especially a very electronegative atom. What can it do? It withdraws electron density (redistribution) from the rest of the molecules( hydrogens). In another words, it pulls stronger on the electron density of the 3 hydrogen to compensate for the electron density donated to make up for the density contributed to making the sigma bond. Hydrogens become more electron deficient than when they were in H2O. Same reasoning can be applied to NH3. I wont rewite this again for ammonia. Below is the statement I made in the previous post. Yout can also think of in terms of physics. Protons of an atom are always concentrated in an atom and surrounded by movable electron cloud. One more thing to add. If you have learned a nitrate group as a meta directing group on benzene, it will be also obious to you. The nitrate group is electron withdrawing because it has a nitogen directly connected to the benzene ring and it has a positive formal charge on it.

Bro, sorry for the post above. I was being little bit harsh on you in the last post. I want to apologize for it. One more thing for clarification. It is not highly electronegative hydrogen stealing electron density from Nitrogen. It is the positive charge on nitrogen pulling electron density from hydrogen atoms that make ammonium more acidic than ammonia. Lets start with ammonia, the nitrogen has zero formal charge. Once it donates its electron pair to a proton, it gains a + charge, whcih makes it electron deficient, so it has a stronger pull on electrons from hydrogen atoms through inductive effect. This will in turn make hydrogen even more electron deficient than when it was in ammonia. The hydrogen are more prone to accept electron pair from electron donors. Remember, acid are electron accepters, and bases are electron donors. I really have to go back to my own studies. MCAT is coming up very soon.

 

[Chrisz]

@Teleologist, probably the nitro group a directing group is not a good example. Think you gonna find somewhere else that you will claim that it is due to the resonance effect. But indeed, it is a combination of inductive and resonance effect