Test for Ammonia: NaOH & Litmus/HCl

[enc08]

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.

 

[Borek]

Your reaction equation is wrong.

It is about NH₄⁺ being neutralized by NaOH to produce conjugate base.

 

[enc08]

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.

 

[Borek]

Ammonia evolves after being neutralized by the strong base:

NH₄⁺ + OH^- → NH₃↑ + H₂O

 

[enc08]

I see. From what I understand, 'evolves' means that it turns into gas?