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Author Topic: NH3 absorption by H2SO4  (Read 24044 times)

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Bentley

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NH3 absorption by H2SO4
« on: April 18, 2005, 05:39:13 AM »

Hello all,
I am brand new to this forum, but glad I have come across it! I was never incredibly strong in chemistry throughout highschool and undergraduate university, but now in grad school I've been forced to face my fears, SOMEWHAT! ;)
Anyway, I just want to make sure I'm on the right track with my calculations.
Essentially part of my research involves the measurement of ammonia (NH3) emissions during the composting a livestock manure. I am passing composter exhaust air through a gas scrubber containing 1.8 N sulfuric acid (H2SO4).
Firstly...would the balanced equation for this reaction be as follows:
2NH3 + H2SO4 ----->[NH4]2SO4 ??

In other words, is it safe to assume that each unit of H2SO4 will combine with 2 units of NH3?

So...if I have 200 ml of 1.8N (0.9M) H2SO4, would the maximum amount of NH3 absorbed (in theory) be:
0.200L X 0.9 X 2 = 0.36 moles NH3 = (.36g)(17g/mole) = 6.12g NH3, or  5.04g NH3-N

Any assistance would be greatly appreciated!
Thanks in advance

Bentley
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Borek

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Re:NH3 absorption by H2SO4
« Reply #1 on: April 18, 2005, 12:28:04 PM »

Firstly...would the balanced equation for this reaction be as follows:
2NH3 + H2SO4 ----->[NH4]2SO4 ??
In other words, is it safe to assume that each unit of H2SO4 will combine with 2 units of NH3?

Yes.

Quote
So...if I have 200 ml of 1.8N (0.9M) H2SO4, would the maximum amount of NH3 absorbed (in theory) be:
0.200L X 0.9 X 2 = 0.36 moles NH3 = (.36g)(17g/mole) = 6.12g NH3, or  5.04g NH3-N

Something is wrong with the units (.36g is wrong) but you are OK for the second time :)
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Bentley

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Re:NH3 absorption by H2SO4
« Reply #2 on: April 19, 2005, 04:13:19 AM »

Hi Borek,
Thanks for the response. I noticed after I had posted that I put 0.36g instead of 0.36 moles. Oh well, I'm glad I got everything else right.

I have another question re: calculating the pH of an acidic solution.

If we use my 1.8N H2SO4 solution,
would the pH = -log[1.8]?

Thanks again

B.
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Borek

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Re:NH3 absorption by H2SO4
« Reply #3 on: April 19, 2005, 05:03:36 AM »

If we use my 1.8N H2SO4 solution,
would the pH = -log[1.8]?

Yes and no.

Yes - that's a way you do it.

No - in such concentrated solution you must account for ionic strength and activity coefficients to calculate anything with reasonable precision.

To say the truth this solution is so concentrated that even activity calculations won't help much.
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miaskows

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Re:NH3 absorption by H2SO4
« Reply #4 on: May 14, 2005, 05:01:17 AM »

Water solutions of  (NH4)2SO4 have acid reaction
( NH3 is weak base and H2SO4 is strong acid).Consequently if you want to assure that you still absorb NH3 with H2SO4 you have to measure pH of scrabbing solution. End point , indicates that you already spent all of H2SO4 is around pH=3-5. If pH of your absorbtion medium has raised above that value, it is pointed on beginning of absorbtion of NH3 with water. NH3 is dissolved in water (absorbtion of NH3 in water scrabbers is the main method for it's recuperation) , but such solutions are not stable if NH3 contaminated with inert flow (as air,CO2 etc) or hot.Equilibrium concentration of NH3 in water depends on it's concentration in inert flow and temperature of the solution.In the other hand due to very low bufferity of the diammonium sulfat water solutions, raising of pH should be very fast and easily detectable. (It should take only tiny excess of NH3 relatively to H2SO4 to bring pH up to 8-10). Besides you need not to use stoichiometric amounts of reagents. You can (and must) stay with some excess of H2SO4 in spent solution . Common used analitical route for determination of NH3 in spent absorbtion solutions could be described as follows:
1.The spent solution weighted and treated with big excess of strong alkali (water NaOH)
2. Resulted strongly alkali solution (or slarry) is heated in a flask and escaped gaseous NH3  absorbed in cooled water trap.
3.Most of the water distillated from alkali solution and collected in cooled receiver.
Water distillate to be collected untill his pH dropped up to ~7
5. Combined distillates to be titrated with HCl .
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