Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Anson on April 13, 2005, 09:26:53 AM
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What is the Acid Dissociation Constant Ka for nitric acid?
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VERY, VERY, VERY HIGH. Nitric Acid is a very strong acid and for all intents and purposes completely dissociates upon dissolution in water.
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MUCH MUCH lover then jdurg thinks :)
http://www.chembuddy.com/?left=BATE&right=dissociation_constants (http://www.chembuddy.com/?left=BATE&right=dissociation_constants)
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But those are pKa values and are even stated to be 'not so accurate'. ;D Here's a pretty good table (http://www.saskschools.ca/curr_content/chem30/modules/module6/acid.html) and you can see that the Ka of Nitric Acid is 24. Yes it's not insanely high, but compare that with the Ka of acetic or oxalic acid and it's substantially higher. ;D
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But those are pKa values and are even stated to be 'not so accurate'. ;D Here's a pretty good table (http://www.saskschools.ca/curr_content/chem30/modules/module6/acid.html) and you can see that the Ka of Nitric Acid is 24. Yes it's not insanely high, but compare that with the Ka of acetic or oxalic acid and it's substantially higher. ;D
So that means pKa for nitric acid is -1,38. Is that high?
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But those are pKa values and are even stated to be 'not so accurate'.
I know, I wrote it by myself :)
Ka of Nitric Acid is 24.
Which is - as Garneck already stated - not far from the value in my table.
Yes it's not insanely high, but compare that with the Ka of acetic or oxalic acid and it's substantially higher.
Yes, but when compared with HClO4 or HCl it is substantially weaker. Nitric acid is probably the weakest of the strongest :)
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http://daecr1.harvard.edu/pka/InorganicAcids.GIF
That's the table from Evan's Harvard class. It's probably decently accurate.
If you want a nice strong acid, why not try 'magic acid'? (This is NOT the kind of magic acid that limpet likes)
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http://daecr1.harvard.edu/pka/InorganicAcids.GIF
That's the table from Evan's Harvard class. It's probably decently accurate.
Thanks, there were a few that I haven't seen before.
However, I feel like I wan't to add my $.02.
I am observing these constants in various sources for about 20 years now. In most cases they were masured two or three times and results were similar - something like -1.3, -1, -1.4 - and they are now quoted again and again, in most cases nobody knows what was the original source and why this or that particular value is better then others. Sometimes sources are quoted but they are often from fifties or even earlier and difficult to check now.
This is not the whole truth at the far end - like HI or HClO4 - where accuracy of measurements is much lower. If the solution is diluted enough to avoid activitiy problems concentration of undissolved acid is often unmeasurable. If the solution is concentrated, activity effects start to play important role and it is not easy to interpolate the results for zero ionic strength.