Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Testing for ammonia

  1. May 4, 2013 #1
    Hi,

    I'm looking at a question which asks how one can test for ammonia in

    [NH4]2Fe[SO4]2

    The answer says that you add sodium hydroxide, and get

    [NH4]2Fe[SO4]2 + 2 NaOH -> [NH4]2Fe(OH)2 + 2 NaSO4

    This is what I don't get: it then says you test the ammonia gas with litmus paper, or with HCL. In the former case, the litmus paper turns blue, and in the latter, you get white smoke.

    My two questions: I know ammonia is alkaline, but how is [NH4]2Fe(OH)2 a gas? Secondly, why do you get white smoke when you add HCL?

    Thanks for your input.
     
    Last edited: May 4, 2013
  2. jcsd
  3. May 4, 2013 #2

    Borek

    User Avatar

    Staff: Mentor

    Your reaction equation is wrong.

    It is about NH4+ being neutralized by NaOH to produce conjugate base.
     
  4. May 4, 2013 #3
    Hi Borek

    I'm beginning to see how it's correct...that the ammonia dissociates in water so it can react.

    Could you please describe what the correct equation is? We haven't looked at conjugate bases, could you elaborate?

    Thanks.
     
  5. May 4, 2013 #4

    Borek

    User Avatar

    Staff: Mentor

    Ammonia evolves after being neutralized by the strong base:

    NH4+ + OH- → NH3↑ + H2O
     
  6. May 4, 2013 #5
    I see. From what I understand, 'evolves' means that it turns into gas?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Testing for ammonia
  1. Detecting Ammonia (Replies: 3)

Loading...