The Naked Scientists

The Naked Scientists Forum

Author Topic: Simple question about ammonia/water solutions  (Read 4920 times)

Offline Somes J

  • Jr. Member
  • **
  • Posts: 13
    • View Profile
Simple question about ammonia/water solutions
« on: 30/06/2011 21:40:30 »
When ammonia dissolves in water some of it reacts to form ammonium and hydroxide ions:

NH3 + H2O = NH4+ + OH-

newbielink:http://scifun.chem.wisc.edu/chemweek/pdf/ammonia.pdf [nonactive]

What happens if you then heat or boil the solution, driving off the ammonia? Does all the NH4+ turn back into NH3?

Just a very basic chemistry question I was wondering about, I can't seem to find the answer on Google.

Thanks.


 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8645
  • Thanked: 42 times
    • View Profile
Simple question about ammonia/water solutions
« Reply #1 on: 30/06/2011 21:53:07 »
Essentially yes, the reaction is driven backwards. The proton moves back from the NH4+ onto the OH- and forms water and ammonia again.
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Simple question about ammonia/water solutions
« Reply #2 on: 30/06/2011 21:59:56 »
I believe you get ammonia (NH3) gas.

Cations rarely exist without their corresponding anions, and it would not be energetically favorable to release cations without anions.  And, some kind of ammonia hydrate NH3H2O would be unlikely to form and remain stable as a vapor.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Simple question about ammonia/water solutions
« Reply #3 on: 05/07/2011 15:14:46 »
NH3(gas over the solution) reversible arrow NH3(gas dissolved in water) reversible arrow NH4+ + OH-.

If you reduce the partial pressure of NH3(gas over the solution) then equilibrium shifts to the left so ammonium ions react with hydroxides ions to form dissolved ammonia which then escapes the solution. Now, this happens when there is equilibrium, but if you leave the solution in open atmosphere, you don't have because the ammonia is not present (or very little) in the air. However the reaction moves to the left only at very little speed, at room temperature. Heating the solution you increase that speed.
 

The Naked Scientists Forum

Simple question about ammonia/water solutions
« Reply #3 on: 05/07/2011 15:14:46 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length