[Scyther_88]

Hello, I started a post regarding the composition of an unknown salt a few days ago. After lab yesterday, I found out that my unknown salt contains sulfide as the anion.

What cation combined with sulfide would make a green powder?? I looked up the possible cations, Cu, Fe, Cr, Ni, Ag, Pb, Bi, Sb4, Sb5, Sn2, Sn4, Al, Zn, but I have not gotten a positive answer. I am 100% the sample contains sulfide...but what on earth can the cation be? Please share your thoughts so I can do some definitive tests tomorrow in lab. It's my last day. Thank you.

[Scyther_88]

Please help. I just need some direction.

By the way, the green salt turned into a bright yellow clear soln. when it dissolved in 12M HCl. I don't know if this helps.

[enahs]

Either your wording is confusing me, or you are mixing things up.

You ask which cation would make a green precipitate with sulfide. Yet, you say you found out your unknown salt contains a sulfide. But you also do not know what cation is in your salt?

See the problem

The unknown cation in your unknown most likely did not react with the sulfide in your unknown to produce the green precipitate.

Or are you saying you are starting with a green powder?

Quick review of everything you did and what you know.

[Scyther_88]

Okay, this is what I know so far:

My original sample was a green powder.

It was insoluble in water, but soluble in both 3M HCl and 3M HNO3. The solution turned clear when it dissolved in the acids.

The sample was insoluble in both 3M and 6M NaOH. However, it was soluble in 6M NH3. It was only slightly soluble in 3M NH3.

The solution was also clear when the sample dissolved in the 6M NH3.

I did a confirming test for sulfide, phosphate, and sulfite, and found that the test for sulfide was positive. Thus, I know from my original green inorganic salt, the anion is sulfide.

However, what is my cation?

The choices are:  Cu, Fe, Cr, Ni, Ag, Pb, Bi, Sb3, Sb4, Sn2, Sn4, Al, Zn. I don't know that any of these would form a green powder substance with sulfide.

[enahs]

Your solubilities seem to be contradicting any common green powder one would find in a education lab. Even from a really mean professor trying to make things hard.

Are you sure you did not make a mistake in your notes or lab? Anybody else in your class get the same compound and you can compare with their notes?

[Scyther_88]

No, I'm sure I didn't make a mistake. I did the solubility tests twice. And no, I can't compare notes with someone else considering everyone got a different compound.

[macman104]

You sure it is Sulfide (S^2-) and not Sulfate (SO₄^2-)

[Scyther_88]

sulfates are soluble in water. This wasn't soluble in water.

[macman104]

sulfates are soluble in water. This wasn't soluble in water.

Careful, there are exceptions to that rule.  However, none of those exceptions are listed in your possible cations, so it's moot.  I was just checking.

Anyway, you might want to look at the following sites:

Link 1
Link 2
Link 3

[DrCMS]

I remember a story from my universities days.  In the analysis lab there was a very annoying cocky student (no not me) who thought he knew everything.  So the lecturer gave him a purple salt to identify.  All the tests came back as Sodium and Chloride as the only ions present with no organic compounds either.  He knew it couldn't just be NaCl beacuse it was purple, right?  What the student didn't know was the lecturer had taken some NaCl down to the basement Co-60 source and irradiated the hell out of it producing purple sodium chloride. 

[Arkcon]

Like DrCMS: says, they are allowed to deliberately confuse you in a variety of ways, one way -- adding organic dyes to color your unknown.  One class we were given contained any of 4 different salts, one possible one, Cu.  One guy found all spot tests failing for him, even though he had a blue solution, turns out his results were correct, he was given none of the 4 ions in question, just plain water dyed blue.  Check with your instructor to see if they'll give you any insights about what info you're supposed to use, for example the initial color of the solid.  'Tho probably, they won't want to give up any of their secrets.

[Borek]

I still wonder how it is possible you have found sulfide by test, but you have not smelled it when dissolving in concentrated acid. What was the sulfide test you did?

I don't remember blue nor green sulfide, all that I recall were yellow, brown or black.

[AWK]

The choices are:  Cu, Fe, Cr, Ni, Ag, Pb, Bi, Sb3, Sb4, Sn2, Sn4, Al, Zn. I don't know that any of these would form a green powder substance with sulfide.

What does mean Sb3, Sb4, Sn2, Sn4?

No sulfides of these metals are green. Only As2S3 or As2S5 are soluble in concentrated ammonia (both sulfides are yellow).

[Borek]

Most likely Sb³⁺, Sb⁴⁺ and so on.

[AWK]

Sb⁴⁺ on analytical chemistry?