Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: onefear on August 27, 2009, 05:43:27 PM
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right so im doing Advanced Higher Chemistry (equivelent to first year course in university)
and for my project i want to create an acid independant of water.
So my question is, is it possible to isolate a lewis acid from solution so that i can compare it with a normal acid?.
Thanks for the help
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an acid independant of water.
What do mean exactly?
So my question is, is it possible to isolate a lewis acid from solution so that i can compare it with a normal acid?.
What is 'a normal acid' in this context?
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well a normal acid requires H2O and can be measured using the pH scale
so for instance
-->
H2O H+ + OH-
<----
you then add say Na+ which removes the OH- shifts the equlibrium to the foward reaction and leaves an excess of H+ ions, you have your acid
but lewis acid is based on the principle that an acid is an electron pair donator or acceptor
so you have say a reaction like this
-->
NH4 NH3- + H+
<----
where adding say Na+ will remove the ammonia ions to leave an excess of H+ ions, and there you also have an acid
the only problem is NH3- + H+ are in solution
and since my project is to create an acid independent of water i need to find out if i can extract the lewis acid from solution once it's ready..?
Note that the pH scale doesn't apply to a lewis acid.
however i intend to create a theoretical pH scale for my lewis acid during my project.
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In pure liquid ammonia, ammonia can ionize like this:
2NH3 ::equil::NH4+ + NH2-
And you can distil acid solutions but you can't get 100% pure acid because acid molecules form hydrates with H2O
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thank you but how to i get the ammonia to ionize?
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thank you but how to i get the ammonia to ionize?
You don't have to - it ionizes when pure and liquid by itself, just like water does.
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so how much pressure would i have to apply to achieve this?.
And what do you mean by distil acid solutions as in solutions that use the pH scale?. if thats the case wouldn't that stop it being an acid as there's no water to form H+ ions?.
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so how much pressure would i have to apply to achieve this?
To make liquid ammonia? Depends on the temperature.
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thank you but how to i get the ammonia to ionize?
You don't have to - it ionizes when pure and liquid by itself, just like water does.
Except that the dissociation constant is almost 20 orders of magnitude smaller.
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Except that the dissociation constant is almost 20 orders of magnitude smaller.
Yep, [NH2-][NH4+]=10-32.
Sulfuric acid will be much better example:
[H3SO4+][HSO4-]=10-2.9
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hmm well could you please give me a reasonable pressure and temperature that i could achieve liquid ammonia in a school lab.
unfortunately sulphuric acid requires water
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I doubt anyone will allow use of liquid ammonia in the school lab.
Sulfuric acid reaction - the one I wrote - occurs in anhydrous acid.
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dont worry they do your american version of school is different from our scottish version
so any idea roughly what pressure and temperature i could do it at?.
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although if that sulphuric acid one is a lewis acid, independant of water and easier to make then please do tell. :)
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your american version of school
No american schools in the 6000 km radius from here ;)
so any idea roughly what pressure and temperature i could do it at?
-34 deg C and atmospheric pressure will do. Still, it is not a chemical that you wan't to work with. Concentrated sulfuric acid is much more easy to handle and much less dangerous - it is not volatile, it won't boil at room temperature, it doesn't emit poisonous vapor and so on.
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ahhh yes poland that is quite a bit away from america haha
thanks i've got a fume cupboard so im ok for poisonous fumes.
The only tricky bit would be keeping it in liquid form
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so how do you remove it from solution?. The only Sulphuric acid i know is always in an aqueous solution.
In it's concentrated form it is a lewis acid yes?, and can it be measured with the pH scale?.
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hmm ok so i've went and done some research
found out aboout anhydrous sulphuric acid, but i can't find out how to make any.
Can you help me out please
Thanks
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Time for shopping most likely.
OTOH, you may also try acetic acid - glacial acid (that is, one without water, that can be easily bought) behaves similarly:
[CH3COO-][CH3COOH2+]=10-15.2
Of all substances listed so far this is probably easiest to find, and most safe.
Other substances to consider - ethanol:
[C2H5O-][C2H5OH2+]=10-18.9
and methanol:
[CH3O-][CH3OH2+]=10-16.7
Both should be easy to find in anhydrous form.
Note, that even if these substances are bought or prepared anhdyrous, just opening the jar/bottle means contaminating them with water.