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Offline hamza

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Acidity!!
« on: 07/10/2007 07:02:02 »
Is it true that Water is more acidic than Alcohol?? And could anyone please arrange these in increasing order of their acidic character??
Alcohol, carboxylic acids, water, inorganic acids , carbonyl compounds and ethers.


 

Offline rosy

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Acidity!!
« Reply #1 on: 07/10/2007 12:56:22 »
Um, it's not that simple, it depends on the inorganic acid, on the alcohol, on the carbonyl compound, etc.
The acidity of a compound is given by its pKa, which is the dissociation constant for the acid losing its proton in water... the lower the pKa the more acidic the molecule.
The link below gives pKa values for many molecules.
http://www.chem.wisc.edu/areas/reich/pkatable/kacont.htm
 

Offline DrDick

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Acidity!!
« Reply #2 on: 08/10/2007 14:25:42 »
Acidity can also vary with solvent.  Some things are more acidic in some solvents while others are more acidic in other solvents.  It's not usually a huge difference, but I've seen a table of acidity in DMSO, and it has a little different ordering than a table of acidity in water.

Dick
 

Offline DrDick

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Acidity!!
« Reply #3 on: 08/10/2007 14:30:44 »
However, in general, inorganic acids are the most acidic and ethers are the least acidic.  Here's a rough ranking:

inorganic > carboxylic > water > alcohol > carbonyls > ethers

Keep in mind that there is significant overlap in this ranking.  For instance, many inorganic acids are less acidic than many carboxylic acids, and even less than some alcohols.  Yes, water is more acidic than most alcohols.  Aromatic alcohols (e.g., phenols) are one important exception, and halogenation near the OH group can also make alcohols more acidic.

Dick
 

Offline Bored chemist

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Acidity!!
« Reply #4 on: 08/10/2007 21:00:32 »
Incidentally, you don't need a solvent. You can measure acidity in the gas phase- people generally don't bother.
Probably the commonest inorganic acids on earth are carbonic and silicic. They are both weaker than typical carboxylic acids like acetic.
 

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Acidity!!
« Reply #4 on: 08/10/2007 21:00:32 »

 

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