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Topic: why do chlorine atoms in acid molecules lower the pH so much?  (Read 7934 times)

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Offline jsmith613

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why do chlorine atoms in acid molecules lower the pH so much?
« on: August 31, 2009, 11:24:02 AM »
why do chlorine atoms in acid molecules lower the pH so much?

Offline bstapes99

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #1 on: August 31, 2009, 12:48:07 PM »
What type of acids are you working with? And what specific acid, for that matter, are you concerned with?
If its something like Hydrochloric Acid, HCl, then the answer is because its a strong acid that dissociates almost completely in solution.

Offline kapital

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #2 on: August 31, 2009, 01:09:06 PM »
I think the question was moore in organic carboxylic acids when the presence of the chlorie decreses pH.

Offline jsmith613

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #3 on: August 31, 2009, 01:34:02 PM »
What type of acids are you working with? And what specific acid, for that matter, are you concerned with?
If its something like Hydrochloric Acid, HCl, then the answer is because its a strong acid that dissociates almost completely in solution.

Yes i was referring to HCl, but how does it dissociate due to Cl2

Offline Borek

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #4 on: August 31, 2009, 02:51:27 PM »
Yes i was referring to HCl, but how does it dissociate due to Cl2

Please elaborate, what you wrote doesn't make any sense.
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Offline jsmith613

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #5 on: August 31, 2009, 03:15:25 PM »
Quote
Please elaborate, what you wrote doesn't make any sense.

What I mean is bstapes99 said
Quote
If its something like Hydrochloric Acid, HCl, then the answer is because its a strong acid that dissociates almost completely in solution.
And what I am saying is, what has that got to do with the presence of Chlorine as my questions is
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why do chlorine atoms in acid molecules lower the pH so much? [/quoute]

Offline Arctic-Nation

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #6 on: August 31, 2009, 03:31:30 PM »
You're still not making all that much sense. The (Bronsted) acidity of any compound is ruled by the stability of the corresponding anion, and there is a clear correlation between acidity and the presence of electronegative elements (or functional groups).
Hydrochloric acid is a strong acid because its dissociation yields a very stable chloride anion. Cl2 is actually completely unrelated, as its dissociation (in water) will not result in the formation of hydrochloric acid, but hypochlorous acid.

Offline jsmith613

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #7 on: August 31, 2009, 03:53:48 PM »
You're still not making all that much sense. The (Bronsted) acidity of any compound is ruled by the stability of the corresponding anion, and there is a clear correlation between acidity and the presence of electronegative elements (or functional groups).
Hydrochloric acid is a strong acid because its dissociation yields a very stable chloride anion. Cl2 is actually completely unrelated, as its dissociation (in water) will not result in the formation of hydrochloric acid, but hypochlorous acid.

but this does not answer the original quesiton. What is it about Cl that causes it to give Acids such as HCl such a low pH

Offline Arctic-Nation

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #8 on: August 31, 2009, 05:09:22 PM »
First of all, chlorine only gives one acid such as HCl, and that is HCl itself. It seems like you want to have a talk about acidity, which is perfectly fine, but refuse to consider anything but HCl.
Second, I'll give you what you want. HCl is a strong acid because chlorine is a very electronegative element (second only to fluorine), which means that the dissociation of HCl gives a very stable chloride anion. Other effects to consider are bond strength (which is rather small) and hydration energy (which measures the stabilization of the ions). There's more to it, but I'm afraid it will be too difficult for you.
Either way, if you really want to know why HCl is a very strong acid, you will have to compare it to other acids to understand all possible influences.

Offline jsmith613

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #9 on: September 01, 2009, 08:09:03 AM »
First of all, chlorine only gives one acid such as HCl, and that is HCl itself. It seems like you want to have a talk about acidity, which is perfectly fine, but refuse to consider anything but HCl.
Second, I'll give you what you want. HCl is a strong acid because chlorine is a very electronegative element (second only to fluorine), which means that the dissociation of HCl gives a very stable chloride anion. Other effects to consider are bond strength (which is rather small) and hydration energy (which measures the stabilization of the ions). There's more to it, but I'm afraid it will be too difficult for you.
Either way, if you really want to know why HCl is a very strong acid, you will have to compare it to other acids to understand all possible influences.

So if i compare it to something like H2SO4 then what is the difference? thanks

Offline jsmith613

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #10 on: September 01, 2009, 10:46:51 AM »
Quote
So if i compare it to something like H2SO4 then what is the difference? thanks

As well as H2SO4  compared to HCl, what about HCLO compared to HCL

Offline bstapes99

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #11 on: September 01, 2009, 11:15:30 AM »
If you want to compare them, find a chart of the strength of these acids (also known as the acid dissociation, or Ka). I have a cheat sheet for my class that says there are 8 strong acids and the rest are weak. By the way, its HCl not HCL (the L isnt capitalized).
Also, just in case you don't understand why the Cl is important, HCl dissociates into H+ and Cl- ions. Because the original bond between the two was weak, this happens to most of the HCl. And all we're worrying about is the concentration of H+ ions (which is the same as the concentration of Cl- ions). Sorry if I'm repeating what the others have said.

Offline jsmith613

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #12 on: September 01, 2009, 11:50:33 AM »
If you want to compare them, find a chart of the strength of these acids (also known as the acid dissociation, or Ka). I have a cheat sheet for my class that says there are 8 strong acids and the rest are weak. By the way, its HCl not HCL (the L isnt capitalized).
Also, just in case you don't understand why the Cl is important, HCl dissociates into H+ and Cl- ions. Because the original bond between the two was weak, this happens to most of the HCl. And all we're worrying about is the concentration of H+ ions (which is the same as the concentration of Cl- ions). Sorry if I'm repeating what the others have said.

I understand that, but how do the Chlorine atoms make the pH so low. H+ ions cause something to be acidic but how do the Cl atoms themselves lower the pH (or is it just they make the molecules easy to dissociate)

Offline Borek

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #13 on: September 01, 2009, 12:08:13 PM »
how do the Cl atoms themselves lower the pH

They don't.

Quote
(or is it just they make the molecules easy to dissociate)

This is much closer.
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Offline jsmith613

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Re: why do chlorine atoms in acid molecules lower the pH so much?
« Reply #14 on: September 01, 2009, 02:48:02 PM »
Quote
This is much closer.

Does that mean it is correct

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