Sciencemadness Discussion Board

How to titrate an acid dissolved in acetic acid

mycotheologist - 26-6-2012 at 15:21

I made a solution of HCl in glacial acetic acid and I'm trying to figure out how to determine the exact concentration of HCl in the CH3COOH. At first I thought of using an extremely weak base that can only be protonated by the HCl but that wouldn't work because the end point could never be reached considering the solution would remain acidic due to the acetic acid.

Paddywhacker - 26-6-2012 at 16:00

See this thread.

Poppy - 26-6-2012 at 17:21

I would strongly suggest a fisherman's pH meter. It works much better. Adding loads of electrolytes makes the pH measure innacacurate. Hopefully that i'll make you to the point. Lol.

[Edited on 6-27-2012 by Poppy]

[Edited on 6-27-2012 by Poppy]

blogfast25 - 27-6-2012 at 04:28

Quote: Originally posted by Paddywhacker  
See this thread.


That thread isn't about GLACIAL acetic acid as a solvent.

Quite a bit of information can be gleaned from the relevant Wiki entry:

http://en.wikipedia.org/wiki/Nonaqueous_titration

Titration of a very weak base like pyridine (in GAA) with a solution of perchloric acid (in GAA) appears possible. Perhaps titration of HCl (in GAA) with pyridine (in GAA) is also possible?



[Edited on 27-6-2012 by blogfast25]

weiming1998 - 27-6-2012 at 05:30

I would suggest redox titration. Add KMnO4 or MnO2 to your HCl/acetic acid. Chlorine gas and crystals of MnCl2 would form. When the solution turns purple (KMnO4) or the MnO2 stops dissolving, the titration is over. Acetic acid does not react with KMnO4 under normal conditions.

blogfast25 - 27-6-2012 at 05:49

Quote: Originally posted by weiming1998  
I would suggest redox titration. Add KMnO4 or MnO2 to your HCl/acetic acid. Chlorine gas and crystals of MnCl2 would form. When the solution turns purple (KMnO4) or the MnO2 stops dissolving, the titration is over. Acetic acid does not react with KMnO4 under normal conditions.


That's not a bad idea, weiming. Dilute the GAA/HCl solution a bit first and that probably should work.

unionised - 28-6-2012 at 04:47

Argentimetry?

blogfast25 - 28-6-2012 at 05:16

Quote: Originally posted by unionised  
Argentimetry?


Yep. Bit expensive...

unionised - 28-6-2012 at 05:30

Silver is recyclable.

blogfast25 - 28-6-2012 at 05:33

But you have to have some to begin with... ;)

DJF90 - 28-6-2012 at 06:59

Its also not THAT expensive. I've just bought 10g for about £8. Can't complain, and it'll suffice my analytical needs.

Hexavalent - 28-6-2012 at 07:43

I got about 4g for free from school: they had demonstrated the silver nitrate/copper reaction several times and were just going to throw out the silver produced, so I turned up with my vial and salvaged it.

blogfast25 - 28-6-2012 at 10:29

Quote: Originally posted by DJF90  
Its also not THAT expensive. I've just bought 10g for about £8. Can't complain, and it'll suffice my analytical needs.


I just bought some myself, about the same price. Bit of a battle to get it at the right price, though...

weiming1998 - 29-6-2012 at 00:45

Quote: Originally posted by blogfast25  
Quote: Originally posted by unionised  
Argentimetry?


Yep. Bit expensive...


Not to mention that any additional chloride ions will mess up the result, plus the nitric acid produced might redissolve the AgCl precipitate at high enough concentration, unless the Ag+ ion is in the form of silver acetate.

But then again, my idea of redox titration wouldn't be good if there are reducing contaminants (like ethanol) in the glacial acetic acid. Perhaps I could ask the original poster whether the GAA is home-made or lab grade?