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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: mc_75 on June 10, 2011, 10:47:59 AM

Title: ammonia - acetic acid
Post by: mc_75 on June 10, 2011, 10:47:59 AM

good morning,

my memories in chemistry is very far....

i have an aqueous solution containing nitrogenous compounds and organic acids. i am quite sure that the nitrogenous compunds are ammonia and the organic acids are above all (99%) acetic acid.
the ph of the solution is 7.1

if I put the solution in a spectrophotometer i find that 12 mg/l are ammonium and 3238 mg/l are total nitrogen. ch3cooh is 4338 mg/l
is it possible that all the ammonia has reacted  with ch3cooh to form the acetate ? in this cas is possible that all the ammonia has reacted ?
if i add NaOH  in order to increase ph to about 9 can I obtain the dissociation of the acetate ? and how much is the grade of dissociation ?

another question how much NaOH per liter have i to add in order to increase ph to 9 ?

thank you very much

please help !!!

massimo

Title: Re: ammonia - acetic acid
Post by: Borek on June 10, 2011, 04:24:01 PM

At pH 7.1 over 99% of ammonia should be protonated. Adding base will convert NH₄⁺ to NH₃, but at pH 9 still over 50% will be in the form of NH₄⁺.

Title: Re: ammonia - acetic acid
Post by: mc_75 on June 15, 2011, 05:31:17 AM

thank you very much for your answer.

now I have to understand the concentrations:

the spectrophotometer is not so good because the total nitrogen test and the ammonia test give contrasting results. maybe the different dilutions and the different reagents could influence the tests.

So i would like to know the quantity of nh3/nh4+ in solution by analytical way. is it possible?
in order to calculate an hypothetical stripping plant, is it possible to calculate the soda consumption per liter of my solution, without knowing the real concentraions of ammonia or acetic acid ? the only data is the start ph and the final ph.

thank you again