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Topic: pH of Ammonium Nitrate  (Read 48092 times)

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Offline J-Mart

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pH of Ammonium Nitrate
« on: March 18, 2008, 09:52:31 PM »
I am given a solution of .1M Ammonium Nitrate and asked to calculate the pH. I do not know how to even really begin in dissociating it down into ions. Here's what I know:

NH4NO3(aq) --> N2O(g) + H2O(l)

H2O <==> H+ + OH-

I don't really know how to pull it all together or if I am even on the right track. 

Offline LQ43

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Re: pH of Ammonium Nitrate
« Reply #1 on: March 18, 2008, 11:43:46 PM »
No, not quite on the right track.

NH4NO3 --> NH4+  +  NO3-

which one of these ions will affect pH?


then check this out
http://www.chembuddy.com/?left=pH-calculation&right=pH-salt-solution

Offline boesmanprinses

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Re: pH of Ammonium Nitrate
« Reply #2 on: March 19, 2008, 03:41:09 AM »
Actually when AmoniumNitrate is heated up you will get N2O and 2H20
NH4NO3 ----> N20 +2H2O

If I am Wrong Please tell me?? and State youre reason

Offline Borek

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Re: pH of Ammonium Nitrate
« Reply #3 on: March 19, 2008, 04:46:02 AM »
It decomposes - slowly. You will have plenty of time to measure pH :)
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline AWK

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Re: pH of Ammonium Nitrate
« Reply #4 on: March 19, 2008, 04:49:26 AM »
Actually when AmoniumNitrate is heated up you will get N2O and 2H20
NH4NO3 ----> N20 +2H2O

If I am Wrong Please tell me?? and State youre reason
This is out of subject (frankly saing, a very narrow temperature range is needed).
Use Ka of NH4+

AWK

Offline chienbinhnam2324

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Re: pH of Ammonium Nitrate
« Reply #5 on: March 20, 2008, 12:17:21 PM »
You were wrong ! When we heat the solution of ammonium Nitrate , there will be exist the equation that NH4NO3 --> N2O + H2O
In the water , NH4NO3 is dissolved into NH4+ and NO3-
There is a reversible equation :
NH4+ <=> NH3 + H+ Ka
and then we have a solution for this problem .

Offline AWK

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Re: pH of Ammonium Nitrate
« Reply #6 on: March 20, 2008, 12:32:39 PM »
You were wrong ! When we heat the solution of ammonium Nitrate , there will be exist the equation that NH4NO3 --> N2O + H2O
In the water , NH4NO3 is dissolved into NH4+ and NO3-
There is a reversible equation :
NH4+ <=> NH3 + H+ Ka
and then we have a solution for this problem .

when we heat solution, nothing is happen. For thermal decomposition we need higher temperature

What des mean this eqution?
AWK

Offline Borek

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Re: pH of Ammonium Nitrate
« Reply #7 on: March 20, 2008, 12:48:33 PM »
You were wrong !

Who "you"? 5 people posted earlier in this thread.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Saint

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Re: pH of Ammonium Nitrate
« Reply #8 on: March 20, 2008, 02:35:36 PM »
Well NO3- does not react with water (dissolve in water i mean, or ionize in water, Actually i am new one here and i am not adapted with english words of Chemistry) because the conjugative(συζυγες for those who are Greek) acid is strong

So
NH4NO3 ->NH4+ + NO3-

goes to

NH4- + H2O -> NH3 + H3O+

If we know Kb of NH3 which is i think 10-5
with Kw we have Ka=Kw/Kb
If it's 25oC Kw=10-14 so Ka=10-9

Ka=[NH3][H3O+]/[Nh4+]

then
[NH3]=[H3O+]=x
[Nh4+]= C-x=1-x

so
10-9=x2/1-x
Ka/C<0,01 so from the approximate calculation we have:
10-9=x2
PH=5-1/2log10=4,5

Is that solution ok. I tried to be complete...
(By the way Hi Everyone!)

E=mc2

Offline Borek

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Re: pH of Ammonium Nitrate
« Reply #9 on: March 20, 2008, 02:54:09 PM »
Well NO3- does not react with water (dissolve in water i mean, or ionize in water, Actually i am new one here and i am not adapted with english words of Chemistry) because the conjugative(συζυγες for those who are Greek) acid is strong

In general - you are right. For the nitpickers, nitric acid is the weakest of strong acids, with pKa=-1.

Your approach seems correct, just Kb of ammonia is 1.8x10-5.

Please read forum rules (especially Answering Questions section).
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Offline AWK

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Re: pH of Ammonium Nitrate
« Reply #10 on: March 21, 2008, 02:00:49 AM »
Quote
Nh4+]= C-x=1-x
The concentration of ammonium nitrate is 0.1, not 1 M.
pH of 0.1 M NH4NO3 is about 4.1 (pH of 1 M - about 4.6)
AWK

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