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Topic: Acid Strength  (Read 9832 times)

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nemzy

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Acid Strength
« on: April 18, 2004, 09:10:24 PM »
Why is HSO3- a stronger acid then H2SO3?

And also, i know that When the size of an atom X increases, the H-X bonds decreases, meaning the strength of the acid increases since more H+ are ionized.

But when when H-X are more electronegitive, doesnt it mean the bonds between the H-X gets stronger, meaning fewer H+ ionizes?? But this is not the case, the more electrongetive the bond between H-X, the acid strength gets stronger. Is my conceptual idea wrong?

Also, lets say you have solutions of NH3, HCl, NaOH, and HC2H3O2 , all with the same solute concetrations. How would you know rank the pH of these solutions from highest to lowest or vice versa?

Offline AWK

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Re:Acid Strength
« Reply #1 on: April 19, 2004, 03:51:48 AM »
HSO3- is weaker (not stronger) acid than H2SO3
K1H2SO3=1.7.10-2, K2H2SO3=6.2.10-8


TRUE


NOT TRUE: HF is a weak acid,
H2S is the weakest acid, H2Se - medium, H2Te the strongest one in this serie.

HCl, CH3COOH, NH3, NaOH - the first one is the most acidic substance, the last one  - most basic
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Re:Acid Strength
« Reply #2 on: April 19, 2004, 04:43:59 AM »
So how exactly can you conclude from the structure of the acid to its strength if not by looking at the electronegativity of the atoms?
How about looking at the stability of the product - the corresponding base?

Offline Mitch

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Re:Acid Strength
« Reply #3 on: April 19, 2004, 04:50:40 AM »
electronegativity is negligeable when compared to the polarizability of the molecule, in general. HI is more polarizable than HF.
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Re:Acid Strength
« Reply #4 on: April 19, 2004, 05:40:35 AM »
Thanks for the response.
I just had a look at google about polarizability and it looks like a pretty complex subject since the polarizability of molecules is linked to its environment and stuff.
Looks like I'm gonna need some freetime to understand this one ;)

Offline jdurg

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Re:Acid Strength
« Reply #5 on: April 19, 2004, 05:07:07 PM »
Also, remember that the most electronegative halogen is fluorine.  Iodine is the least electronegative.  (Aside from Astatine, but we'll just ignore that one ;)).  So the electronegativity actually decreases as you move down the group, thus making the bond between H and the Halogen less "strong."
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Offline hmx9123

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Re:Acid Strength
« Reply #6 on: April 21, 2004, 12:37:48 AM »
HF is a weak acid in polar protic solvents.  In polar aprotic solvents, it is a strong acid. :)

Offline AWK

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Re:Acid Strength
« Reply #7 on: April 21, 2004, 01:34:32 AM »
"HF is a weak acid in polar protic solvents.  In polar aprotic solvents, it is a strong acid"

Can you show such a solvent which is at least as polar as water. Hydrogen bond in H2F2 (this is more correct formula for HF) is very strong (the strongest hydrogen bond ever known?) and only can be broken by strongest interactions than in H2F2 take place.
« Last Edit: April 21, 2004, 01:40:43 AM by AWK »
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Offline hmx9123

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Re:Acid Strength
« Reply #8 on: April 21, 2004, 05:36:08 PM »
Not quite as polar as water, but I have always been taught that HF was a strong acid in polar aprotic solvents, such as DMSO.  Perhaps this is incorrect, but I have heard it in multiple places.  As for the H2F2, I'm sure you're more well read in the subject than myself.  What is your knowledge about HF in, say, DMSO or HMPA, etc.?  I'm curious.

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