What would happen when you mix liquid $\ce{NH3}$ and excess of sulphur?

The answer key states that a solid with $\ce{N}$ and $\ce{S}$, and a gas which gives a black precipitate with lead acetate is evolved.

Surely, $\ce{H2S}$ gas will evolve. What about the solid? Is it ammonium sulphide or ammonium sulphite?

  • $\begingroup$ Are you sure they meant excess sulfur and not sulfur dioxide? The reaction of sulfur dioxide with ammonia is a famous industrial reaction, so that might be the reaction in the test. Though I reckon the products would be the same. $\endgroup$ – M.A.R. Jun 6 '15 at 13:21
  • $\begingroup$ Yes they meant excess sulphur. $\endgroup$ – lucy G Jun 6 '15 at 13:33
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    $\begingroup$ If you’re sure that you only have sulphur and liquid (i.e. cold, pure, not dissolved in water) ammonia, then only one of your two suggestions is possible. $\endgroup$ – Jan Jun 9 '15 at 20:03

I don't think this question has a simple answer.

This paper's first page (all I can see without a subscription) indicates that sulfur can dissolve in liquid ammonia, producing hydrogen sulfide (as the question correctly states) and... complicated stuff: S7N-, which disproportionates into S4N- and "an" ammonium polysulfide (maybe (NH4)2S6, maybe another composition).

The paper's first page also refers to the system's light sensitivity, so if you don't keep it in the dark, you may get different products.

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If you really mean sulfur plus ammonia, then the solid cannot contain oxygen which is not present in the system.

There could be several products, but we would expect some sort of sulfur-nitrogen compound such as $\ce{S4N4}$, a reaction referred to here.

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  • $\begingroup$ We could write any reaction of N and S such that $\ce{x N + y S -> N_xS_y}$. I wish to ask how "we would expect" that only $\ce{S4N4}$ would be formed, and not any other compound (like $\ce{S5N5}$)? $\endgroup$ – Gaurang Tandon Jul 1 '18 at 9:53
  • $\begingroup$ There are multiple sulfur-nitrogen compounds, really. But $\ce{S4N4}$ is a relatively common and well known one. $\endgroup$ – Oscar Lanzi Jul 1 '18 at 10:05
  • $\begingroup$ Okay, I was only worried, even though $\ce{S4N4}$ may be a common and well-known compound, if the reaction conditions allow for its formation or not? $\endgroup$ – Gaurang Tandon Jul 1 '18 at 10:08
  • $\begingroup$ Hard to say. The problem stayement is not very specific. $\endgroup$ – Oscar Lanzi Jul 1 '18 at 12:02

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