can ammonia really lower ph?

[krap101]

i think it was ammonia. ive told this to a couple people, but im not exactly sure myself. like. can someone explain how this happens?

 

[Bubble_B0y]

i don't think ammonia lowers the pH directly, but the nitrogen cycle DOES !!!

the nitrogen cycle process (ammonia --> nitrite --> nitrate) is an acidic process.
Overtime, the pH will decrease because of the accumulation of poo, waste, decaying matter, uneaten food etc....

 

[TomK2]

uhm, I might hurt myself trying to think so far back, but isn't ammonia actually classified as a weak base? Anyone who is a few decades closer to chemistry courses care to comment? Wait, I know! I'll Ask Geeves at ask.com

"Ammonia solutions are basic, due to the hydroxide ions formed in solution. "

Hah! and I didn't even hurt myself.

 

[krap101]

heh im going to take chemistry next year .

i forgot what i heard before. and bubble you were right. i heard that the poop and stuff lowers ph.

lol im going to have so much fun next year.

 

[TomK2]

Decaying matter is known to cause acidic environments, but I am not sure it is related to the nitrogen cycle. Nitrification is rather different than decay, no? Carbohydrates, proteins, and lipids are all decaying at once, and only some of the nitrogen from protein decay will end up as ammonia. Most organic compounds are weak acids, as would be the products of decay. Conversion of ammonia, NH3 to nitrite, NO3 is an oxidation reaction. Oxidation often results in more acidic compounds, so...

uh oh, starting to hurt myself.....

I suppose nitrification could lower pH but I am not sure. Ouch.

ok, having recovered from my headache, I do think nitrification releases hydrogen ions. Man, its been a loooong time. 25 years to be exact.

 

[malkore]

since ammonia is a base, it would increase pH, not lower it. Acids lower pH, which is why stuff like 'pH Down' contain hydrochloric acid.

 

[TomK2]

Malkore-
Do you know if conversion of ammonia to nitrate lowers the pH? I know that if you have lots of nitrite, it forms nitric acid in water, but I do not think nitrate does anything like that. And since the nitrite your bacteria produce is quickly converted to nitrate, I doubt nitrite metablolism in an aquarium leads to any significant nitric acid. I did try and look up the chemical equations for ammonia conversion to nitrate, and I was able to account for all the Nitogens and Oxygens, but I lost track of a few hydrogens. So I wondered if H+ was a byproduct of nitrification. Pure mental excersise here, but sometimes curiosity must be satisfied.

 

[TomK2]

Wait, I used a different search engine and found exactly what I was looking for! bubble boy was right all along. Kudos to you!
http://www.fishdoc.co.uk/filtration/nitrification.htm

Exerpt from the above link:

From ammonia to nitrate

There two bacterial species involved. Nitrosomonas sp. bacteria which oxidize ammonia to nitrite, while Nitrobacter bacteria convert nitrite to nitrate, with both species utilising the energy released by the reactions. This seemingly simple process involves a complex series of reactions that can be summarised in chemist shorthand as:

For Nitrosomonas: 55NH4++ 76 O2 + 109HCO3- C5H7O2N + 54NO2-+ 57H2O + 104H2CO3

For Nitrobacter:400NO2- + NH4+ + 4H2CO3 + HCO3- + 195 O2 C5H7O2N + 3H2O + 400 NO3-

What these reactions tell us in plain language is that;

in equation (1), ammonia (NH4+) is combined with oxygen and hydrogen carbonate to produce bacterial cell mass, nitrite (NO2-) , water and carbonic acid,

in equation (2), nitrite is combined with ammonia, carbonic acid, hydrogen carbonate and oxygen to produce bacterial cell mass, water and lots of nitrate (NO3-).

While this all seems a bit grand and a bit unnecessary there are two important points that come out of these equations.

Approximately 4.3 mg O2 are consumed for every mg of ammonia-nitrogen oxidised to nitrate-nitrogen

8.64 mg of alkalinity in the form ofHCO3- are consumed per mg of ammonia-nitrogen oxidised. This is quite a substantial amount of alkalinity and will over a period of time dramatically change the character of the pond water, affecting both hardness and pH stability. It is also an acidifying process, producing a gradual build up of nitric acid. It should also be noted that the process does not remove any nitrogen from the system; merely changing it from one form to another.

nitrification uses substantial amounts of oxygen and carbonate, reducing water hardness and buffering capacity and has a mild acidifying affect.

end exerpt.


So there! Curiousity has been satisfied. I feel so much better now.

 

[tetrin]

let me see if i can simplify tomk2's equations -

ammonia, which forms ammonium in water, reacts with atmospheric oxygen to form nitrite -
(NH4+) + 1.5O2 -> (NO2-) + H2O + 2(H+)

this reaction is the source of H+ ions that decrease the ph of water over time. and this is one of the major reasons why pwc's are absolutely necessary.

nitrite to nitrate -
(NO2-) + 0.5O2 -> (NO3-)

of course to simplify things, i didn't take into account any organic/inorganic carbon.