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Offline neilep

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Re: The strongest acid...
« Reply #25 on: 21/03/2004 03:39:59 »
quote:
Originally posted by Donnah

quote:
Originally posted by NickNYC
yes, donnah, you're strictly forbidden to think about it because of your woman-ness... that is exactly what i intended and i'm glad you caught that and didn't just go ahead and think of anything because that would be wrong.


Yes NickNYC, we mere women cannot possibly think as well as men.  They have two heads to our one after all, and we know what wonderful decisions men make with the aid of that second head.;)




Thanks Donnah, that's really supportive of you:);), and as males we appreciate your kind understanding and concurrence :D......I just hate it though ,when one head does not do what the other one wants it to do...errhmmmm!!:)[:I][:I]

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Offline MayoFlyFarmer

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Re: The strongest acid...
« Reply #26 on: 21/03/2004 05:30:42 »
[:0][:p]  that could have SO many meanings, NONE of which I was prepared for!

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Offline ruthenium

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Re: The strongest acid...
« Reply #27 on: 04/04/2004 21:46:47 »
HJ is the strongest acid among simple, mineral acids
 

Offline CsManiacDan

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Re: The strongest acid...
« Reply #28 on: 05/04/2004 09:12:53 »
What's Element J? I wasn't aware of an element having the symbol J.

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Offline MayoFlyFarmer

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Re: The strongest acid...
« Reply #29 on: 05/04/2004 13:55:47 »
thank you for asking that, I thought I was even dumber at chemistry than I had previously thought I was.  So...what is "J"??

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Offline gsmollin

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Re: The strongest acid...
« Reply #30 on: 05/04/2004 20:20:30 »
I think ruthenium means HF.
 

Offline ruthenium

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Re: The strongest acid...
« Reply #31 on: 05/04/2004 20:59:02 »
Sorry, it is HI
 

Offline Big_Jules

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Re: The strongest acid...
« Reply #32 on: 09/04/2004 03:18:15 »
I'd like to go right back to Chris' very early comment regarding conception of strength. In distilled water, all 'strong' mineral acids dissocite fully, while many of the weak organic acids dissociate only partially, though that does depend on actual concentration of any given acid, and the resulting pH). As he indicated, strnegth by this definition relates to the ability to generate hydrogen ions, the concentration of which defines pH in a model system.

I'd like to take another angle. Organic acids are used quite widely, either through addition or generation during fermentation processes, as antimicrobial preservatives in foods. At a given, moderate pH, such organic acids prove more effective and could thus be viewed as 'stronger' than  mineral acids in preventing the growth of microorganisms. This is due to the partitioning of dissociated and undissociated acids between the external and internal cell environment, respectively. Undissociated acids (e.g. acetic acid as CH3COOH, rather than CH3COO- and H+) are taken up passively by bugs and accumulate in the cell, lowering pH. The cell has to expend a lot of energy to pump the acid out of the cell. If sufficient acid exists in the food product, it continues to flow into the cell, which eventually becomes exhausted, acid accumulates sufficiently to destroy key cell functions and the cell dies. Imagine being in a boat with a hole in it and having to continually bail out water. Eventually, you get too tired, the boat sinks and you drown! As mineral acids do dissociate, they don't 'behave' this way. If they are used in sufficient concentration to lower external pH sufficiently, then there will be a killing effect, but by then the food is probably too acid to be enjoyable!
 

Offline chris

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Re: The strongest acid...
« Reply #33 on: 09/04/2004 05:56:06 »
Nicely put. So the mineral acids in their non-dissociated form - e.g. vinegar CH3.COOH - can move readily across the lipid membrane (because they are uncharged) of cells. Within the intracellular environment they then dissociate - CH3.COOH -> CH3.COO - + H+ and impede cellular functions in contaminating microbes. Brilliant.

There is actually a human correlate and that's the example of aspirin (acetyl salicylate), which is itself a weak acid. In the stomach, where there is a lot of acid) the aspirin molecule remains un-ionised - in other words it mops up hydrogen ions (H+) - and stays in its uncharged form. In this form it can cross the stomach wall, by using the fact that it is an organic molecule to 'soak' through the lipid in the stomach cell membranes and into the blood stream. Once in the blood (where the pH is weakly alkaline - about 7.4 in an artery - it ionises).

Hence aspirin is one of the few drugs able to be directly absorbed through the stomach wall where most agents rely on the intestine to pick them up.

Chris

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Offline ruthenium

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Re: The strongest acid...
« Reply #34 on: 04/04/2004 21:46:47 »
HJ is the strongest acid among simple, mineral acids
 

Offline CsManiacDan

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Re: The strongest acid...
« Reply #35 on: 05/04/2004 09:12:53 »
What's Element J? I wasn't aware of an element having the symbol J.

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Offline MayoFlyFarmer

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Re: The strongest acid...
« Reply #36 on: 05/04/2004 13:55:47 »
thank you for asking that, I thought I was even dumber at chemistry than I had previously thought I was.  So...what is "J"??

This is a signature.... AND YOU WILL LIKE IT!!
 

Offline gsmollin

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Re: The strongest acid...
« Reply #37 on: 05/04/2004 20:20:30 »
I think ruthenium means HF.
 

Offline ruthenium

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Re: The strongest acid...
« Reply #38 on: 05/04/2004 20:59:02 »
Sorry, it is HI
 

Offline Big_Jules

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Re: The strongest acid...
« Reply #39 on: 09/04/2004 03:18:15 »
I'd like to go right back to Chris' very early comment regarding conception of strength. In distilled water, all 'strong' mineral acids dissocite fully, while many of the weak organic acids dissociate only partially, though that does depend on actual concentration of any given acid, and the resulting pH). As he indicated, strnegth by this definition relates to the ability to generate hydrogen ions, the concentration of which defines pH in a model system.

I'd like to take another angle. Organic acids are used quite widely, either through addition or generation during fermentation processes, as antimicrobial preservatives in foods. At a given, moderate pH, such organic acids prove more effective and could thus be viewed as 'stronger' than  mineral acids in preventing the growth of microorganisms. This is due to the partitioning of dissociated and undissociated acids between the external and internal cell environment, respectively. Undissociated acids (e.g. acetic acid as CH3COOH, rather than CH3COO- and H+) are taken up passively by bugs and accumulate in the cell, lowering pH. The cell has to expend a lot of energy to pump the acid out of the cell. If sufficient acid exists in the food product, it continues to flow into the cell, which eventually becomes exhausted, acid accumulates sufficiently to destroy key cell functions and the cell dies. Imagine being in a boat with a hole in it and having to continually bail out water. Eventually, you get too tired, the boat sinks and you drown! As mineral acids do dissociate, they don't 'behave' this way. If they are used in sufficient concentration to lower external pH sufficiently, then there will be a killing effect, but by then the food is probably too acid to be enjoyable!
 

Offline chris

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Re: The strongest acid...
« Reply #40 on: 09/04/2004 05:56:06 »
Nicely put. So the mineral acids in their non-dissociated form - e.g. vinegar CH3.COOH - can move readily across the lipid membrane (because they are uncharged) of cells. Within the intracellular environment they then dissociate - CH3.COOH -> CH3.COO - + H+ and impede cellular functions in contaminating microbes. Brilliant.

There is actually a human correlate and that's the example of aspirin (acetyl salicylate), which is itself a weak acid. In the stomach, where there is a lot of acid) the aspirin molecule remains un-ionised - in other words it mops up hydrogen ions (H+) - and stays in its uncharged form. In this form it can cross the stomach wall, by using the fact that it is an organic molecule to 'soak' through the lipid in the stomach cell membranes and into the blood stream. Once in the blood (where the pH is weakly alkaline - about 7.4 in an artery - it ionises).

Hence aspirin is one of the few drugs able to be directly absorbed through the stomach wall where most agents rely on the intestine to pick them up.

Chris

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Offline lightarrow

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Re: The strongest acid...
« Reply #41 on: 26/08/2006 23:13:22 »
quote:
Originally posted by Exodus

Can anyone tell me what the strongest acid known to man is, assuming each acid type is of similar molar concentration.[?]
Let's go a bit into science-fiction.

the strongest acid I could think of is...antimatter.

I explain: according to Lewis definition of acidity (more general than the Brownsted one with protons only) an acid is a substance which reacts with another substance's electrons to form a bond. What does react with a substance's electrons more than antielectrons?

You know, when an antielectron approach enough an electron, they disintegrate each other generating a flash of light energy.
(The same with protons and antiprotons)

Incidentally, that would also be the most reactive acid!
 

Offline Mjhavok

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Re: The strongest acid...
« Reply #42 on: 30/08/2006 02:59:43 »
In general scientific usage an acid is a molecule or ion that is able to give up a proton (H+ ion) to a base, or accept an unshared pair of electrons from a base. An acid reacts with a base in a neutralization reaction to form a salt.
 

Offline bostjan

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Re: The strongest acid...
« Reply #43 on: 30/08/2006 06:28:25 »
wouldn't the strongest acid be h3o+?  i know nothing of chemistry.
 

Offline lightarrow

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Re: The strongest acid...
« Reply #44 on: 30/08/2006 15:46:32 »
In general scientific usage an acid is a molecule or ion that is able to give up a proton (H+ ion) to a base, or accept an unshared pair of electrons from a base. An acid reacts with a base in a neutralization reaction to form a salt.

What does exactly mean "...accept an ushared pair of electrons..."?

...It means that it forms a bond with them, and to do it it must take the other specie's electrons!

What does exactly mean "...from a base"? That is, what's exactly a "base"?

It's something able to give its electrons to another species.

In the reaction between an acid and a base, there could form a salt but it could also NOT form any salt! I could make a lot of examples of this, but I'll write only some:

Al3+ + 3H2O --> Al(OH)3 + 3H+ ; Al3+ is the acid and water is the base.

H2SO4 + CH3COOH --> CH3COOH2+ + HSO4- ; H2SO4 is the acid, CH3COOH (acetic acid) is the base!

NH3 + H2O --> NH4+ + OH- ; H2O is the acid, NH3 is the base...

« Last Edit: 07/11/2007 16:42:35 by lightarrow »
 

Offline lightarrow

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Re: The strongest acid...
« Reply #45 on: 30/08/2006 16:38:39 »
quote:
Originally posted by bostjan

wouldn't the strongest acid be h3o+?  i know nothing of chemistry.
This is true only if all the chemical species you are considering are in dilute acqueous solution. Infact, since the water molecule can act as a base (electron pairs on the outer of the oxygen atom), if there existed a stronger acid than H3O+, it would react with water molecules forming H3O+ :

HA + H2O <--> H3O+ + A- ; for protic acids
Acid + 2H2O <--> AcidOH- + H3O+ ; for other acids.

Anyway, from the equilibriums above, we can understand if an acid is stronger than H3O+ : if the reaction is shifted to the right (I'm sorry, I don't know how to translate this exactly into english) then it's stronger than H3O+ , weaker in the opposite case.

Example: which is stronger, HCl or H3O+ ? Amswer: HCl. Why? Because:

HCl + H2O --> H3O+ + Cl- . In this case I didn't wrote two arrows, because the reaction is shifted (goes) completely on the right. So, HCl is much stronger than H3O+.

Wikipedia (http://en.wikipedia.org/wiki/Strong_acid) gives this range of acidity :
Hydroiodic acid HI > Hydrobromic acid HBr > Hydrochloric acid HCl > Perchloric acid HClO4 > Sulfuric acid H2SO4 (Ka1/first dissociation only) > Nitric acid HNO3 > Hydronium ion H3O+.

To measure the acidity of very strong acids, so, it's better to use chemical species less basic than water, for example CH3COOH, because in this case the equilibrium is not completely shifted on the right.

The acidity, then, can be expressed with the "Hammett acidity function".
« Last Edit: 30/08/2006 16:51:48 by lightarrow »
 

Offline bostjan

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Re: The strongest acid...
« Reply #46 on: 31/08/2006 05:40:15 »
ahh, i see.  very good response.
 

Offline bostjan

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Re: The strongest acid...
« Reply #47 on: 30/08/2006 06:28:25 »
wouldn't the strongest acid be h3o+?  i know nothing of chemistry.
 

Offline lightarrow

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Re: The strongest acid...
« Reply #48 on: 30/08/2006 15:46:32 »
quote:
Originally posted by Mjhavok

In general scientific usage an acid is a molecule or ion that is able to give up a proton (H+ ion) to a base, or accept an unshared pair of electrons from a base. An acid reacts with a base in a neutralization reaction to form a salt.
What does exactly mean "...accept an ushared pair of electrons..."?

...It means that it forms a bond with them, and to do it it must take the other specie's electrons!

What does exactly mean "...from a base"? That is, what's exactly a "base"?

It's something able to give its electrons to another species.

In the reaction between an acid and a base, there could form a salt but it could also NOT form any salt! I could make a lot of examples of this, but I'll write only some:

Al3+ + 3H2O --> Al(OH)3 + 3H+ ; Al3+ is the acid and water is the base.

H2SO4 + CH3COOH --> CH3COOH2+ + HSO4- ; H2SO4 is the acid, CH3COOH (acetic acid) is the base!

NH3 + H2O --> NH4+ + OH- ; H2O is the acid, NH3 is the base...

 

Offline lightarrow

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Re: The strongest acid...
« Reply #49 on: 30/08/2006 16:38:39 »
quote:
Originally posted by bostjan

wouldn't the strongest acid be h3o+?  i know nothing of chemistry.
This is true only if all the chemical species you are considering are in dilute acqueous solution. Infact, since the water molecule can act as a base (electron pairs on the outer of the oxygen atom), if there existed a stronger acid than H3O+, it would react with water molecules forming H3O+ :

HA + H2O <--> H3O+ + A- ; for protic acids
Acid + 2H2O <--> AcidOH- + H3O+ ; for other acids.

Anyway, from the equilibriums above, we can understand if an acid is stronger than H3O+ : if the reaction is shifted to the right (I'm sorry, I don't know how to translate this exactly into english) then it's stronger than H3O+ , weaker in the opposite case.

Example: which is stronger, HCl or H3O+ ? Amswer: HCl. Why? Because:

HCl + H2O --> H3O+ + Cl- . In this case I didn't wrote two arrows, because the reaction is shifted (goes) completely on the right. So, HCl is much stronger than H3O+.

Wikipedia (http://en.wikipedia.org/wiki/Strong_acid) gives this range of acidity :
Hydroiodic acid HI > Hydrobromic acid HBr > Hydrochloric acid HCl > Perchloric acid HClO4 > Sulfuric acid H2SO4 (Ka1/first dissociation only) > Nitric acid HNO3 > Hydronium ion H3O+.

To measure the acidity of very strong acids, so, it's better to use chemical species less basic than water, for example CH3COOH, because in this case the equilibrium is not completely shifted on the right.

The acidity, then, can be expressed with the "Hammett acidity function".
« Last Edit: 30/08/2006 16:51:48 by lightarrow »
 

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Re: The strongest acid...
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