Sciencemadness Discussion Board - Help identifying a completely unknown compound

Help identifying a completely unknown compound

Oscilllator - 15-1-2015 at 01:14

I could do with some help from some fellow mad scientists about identifying a compound I found in a jar labelled silver nitrate. I have conducted a battery of tests that I think should narrow it down. Here are my observations:

-The compound is a very pale yellow powder, almost off-white

-The compound is hydrophobic and insoluble in water

-The compound does not appear to decompose under the influence of a propane lamp

-The compound does not dissolve in hot concentrated NaOH

-The compound does dissolve in hydrochloric and nitric acids to give a turbid yellow solution with bubbling. (I can't identify the gasses smell, but it certainly has some kick)

-If the solution is sufficiently concentrated, upon cooling the above turbid yellow solution turns into a wobbly gel! (see picture)

Don't mind the carbon stains, they're from something else entirely

-When heated with 98% sulfuric acid, the compound appears to partially dissolve (although I could be wrong) and the test tube turns brown

-The compound does not dissolve in acetic acid, even when heated

-When added to an acidic permanganate solution, a chlorine smell is observed and after a time the test tube becomes turbid due to a MnO2 precipitate

Does anybody have an idea as to what this compound might be, or to tests that could narrow it down? So far it seems to me that it's *probably* an inorganic chloride of some kind, based on its flame resistance and chlorine smell from the permanganate. But what kind of inorganic chloride dissolves vigorously in an acid???

j_sum1 - 15-1-2015 at 04:03

Quote: Originally posted by Oscilllator

-When added to an acidic permanganate solution, a chlorine smell is observed and after a time the test tube becomes turbid due to a MnO2 precipitate

What acid are you using with the permanganate? If it is HCl, that would account for the chlorine smell and the precipitate.

Edit.
Any results from a flame test?

[Edited on 15-1-2015 by j_sum1]

IrC - 15-1-2015 at 05:05

Are you sure you do not have a mislabeled bottle of Silver Chloride (possibly with impurities)?

phlogiston - 15-1-2015 at 05:31

AgCl does not dissolve in nitric acid and converts into black silver oxide in conc. sodium hydroxide, so that doesn't fit the evidence.

Is it light sensitive?
Is it soluble in concentrated ammonia?
Do you get a precipitate if you add a soluble chloride or sulfate to the (diluted) solution in nitric acid?

Silver iodide and bromide are yellowish.

[Edited on 15-1-2015 by phlogiston]

Fantasma4500 - 15-1-2015 at 06:03

try to dry some of it out and mix up with roughly equal amounts of metal powder (Mg would probably be the best)
perhaps try to see if the gel can dissolve in something like acetone?

Bert - 15-1-2015 at 07:11

Take a tiny bit of it on a clean Pt wire and hold it just above a blue flame of Bunsen burner or methanol burner. How does it behave, and what colors are seen in the flame over sample?

The Volatile Chemist - 15-1-2015 at 09:10

The 'gasses' could be nitrogen oxides from nitrogen, since they have some 'kick'.

Oscilllator - 15-1-2015 at 17:05

Thanks for all the responses everyone, I'll do some more experiments today and get back to you.

Quote:

What acid are you using with the permanganate? If it is HCl, that would account for the chlorine smell and the precipitate.

Good point! I'll go try that with nitric acid now

Quote:

Is it light sensitive?
Is it soluble in concentrated ammonia?
Do you get a precipitate if you add a soluble chloride or sulfate to the (diluted) solution in nitric acid?

1: I'll check.
2:I don't have any concentrated ammonia, but I'll first add NaCl to a soln in HNO3, then try using a NaOH/NH4Cl solution, which should have the same effect.
3: I'll do this before test 2.

Quote:

try to dry some of it out and mix up with roughly equal amounts of metal powder

I only have Aluminium powder, but I'll try with that.

Quote:

Take a tiny bit of it on a clean Pt wire and hold it just above a blue flame of Bunsen burner or methanol burner

I don't have any Pt wire, but I'll try again with a clean stainless steel spatula and report back.

Also, I can tell for sure the gas is not NO2. I know what that smells like.

Oscilllator - 15-1-2015 at 21:46

Quick update before I go to work:

-Placing some on a clean stainless steel spatula and heating with a propane lamp resulted in a strong sodium colour, but this of couse could be contamination, since the spectrum of sodium is so strong. The compound turned slightly black, but this occurred only after heating to an incandescent temperature, so it is probably just some organic contamination. No decomposition of the compound was observed.

-Upon dissolving in HNO3, there was no precipitate upon adding aqueous NaCl or NH4Cl.

-The compound shows no signs of degradation after 40 minutes in full sunlight.

-Even when dissolved in HNO3, the compound still discolours a KMnO4 solution, and a very faint odour of chlorine can be smelt, much fainter than when the compound was dissolved in HCl

- The compound does not dissolve in a concentrated solution of NH4Cl and NaOH, and thus I conclude it also will not dissolve in concentrated ammonia solution

-When cleaning out the test tubes of gel, I noticed that the gel does not appear to melt appreciably, showing the gel is relatively temperature tolerant. Certainly it melts at a far higher temperature than agar gel, a gel that has easily melted under the same circumstances

I hope this helps narrow it down!

phlogiston - 16-1-2015 at 03:47

I think you can exclude it being a silver salt.
Halides would be sensitive to light, yield a precipitate upon addition of chloride to the solution and decompose to black silver oxide in concentrated sodium hydroxide.
Silver chloride and bromide (though not the iodide) would have dissolved in ammonia.

Wild guess: could it be silica gel, perhaps scraped of a TLC plate?

It is likely to be inorganic, given its resistance to strong heating. So, doing precipitation tests from your nitric acid solution (filter it first to get rid of the turbidity), should allow you to narrow down the cation and/or anion.

[Edited on 16-1-2015 by phlogiston]

[Edited on 16-1-2015 by phlogiston]

gdflp - 16-1-2015 at 06:33

If it was silica gel, wouldn't it dissolve slowly in the hydroxide, and not dissolve in an acidic solution? Have you tried a molten fusion with sodium hydroxide? If that works, is it possible that it's contaminated stannic oxide? The yellow color could be due to hydrated SnO contamination, that would make the slight black color when heating in air anhydrous SnO formed by the dehydration.

Random - 16-1-2015 at 06:57

Check is it irganic or inorganic. Check the flame color. Acid and base test. Does it yield precipitate with alkali carbonate. Yes/no. Check color. Go through the periodic table. Eliminate everything that's not. Check more specific things to determine exactly.

The Volatile Chemist - 16-1-2015 at 06:58

If you can get any reaction products to dissolve, try a ferrocyanide or ferricyanide test. They can be rather useful.

gdflp - 16-1-2015 at 07:15

Quote: Originally posted by Random

Check is it irganic or inorganic. Check the flame color. Acid and base test. Does it yield precipitate with alkali carbonate. Yes/no. Check color. Go through the periodic table. Eliminate everything that's not. Check more specific things to determine exactly.

Read through the thread, he already tried a flame test, solubility in acid and alkali, charring, and chloride precipitation.

DJF90 - 16-1-2015 at 09:30

One quick question that no-one seems to have asked; how did you obtain this mislabelled jar of "silver nitrate". Was it something that you've accidentally mislabelled yourself?

Random - 16-1-2015 at 13:32

Quote: Originally posted by gdflp

Quote: Originally posted by Random

Read through the thread, he already tried a flame test, solubility in acid and alkali, charring, and chloride precipitation.

He didn't try to add carbonate to dissolved salt in acid and then analyze the result. He didn't try to incinerate this yellow gel and it probably should dissolve in acid. He didn't try to add reducing agent like bisulphite to non oxidizing acid like acetic.

Wobbly gel looks like very hygroscopic solid.

For example MnO2 seems resistant unless you add reducing agent.

[Edited on 16-1-2015 by Random]

[Edited on 16-1-2015 by Random]

AJKOER - 16-1-2015 at 14:22

AgCO3

gdflp - 16-1-2015 at 14:29

Quote: Originally posted by AJKOER

AgCO3

Nope, that would dissolve in acetic acid, and would precipitate AgCl on addition of chloride.

Oscilllator - 16-1-2015 at 14:47

Righton! On to more experimentation

Quote:

If you can get any reaction products to dissolve, try a ferrocyanide or ferricyanide test

I'll add this to the list of todays experiments.

Quote:

One quick question that no-one seems to have asked; how did you obtain this mislabelled jar of "silver nitrate"

It is a ~150g sample taken from a 30+ year old jar that was about 750ml in volume and was labelled silver nitrate. However I could tell that that jar was not the original jar, as the label was stuck on the side of a ground-glass reagent jar I got it from an old relative who has since died, so no help there...

Quote:

I will do all of these things today! Except I will try metabisulphite, thiosulphate and hydrolysed sucrose instead. Also, the yellow gel was formed upon addition of acid to the compound, so it obviously isn't really soluble in it.

I will also try addition of an iodide today, as well as following up on that aluminium powder reaction I said I would do. I for one am quite disappointed that a silver salt seems out of the question, as there is a decent amount of powder there, and I was hoping to try that N2O5 synthesis mentioned elsewhere

phlogiston - 16-1-2015 at 17:12

Nobody said this yet: please be very careful with it until you have established its identity. For all you know it could be a cyanide, or a compound of thallium, cadmium or mercury.

IrC - 16-1-2015 at 17:26

Quote: Originally posted by phlogiston

Nobody said this yet: please be very careful with it until you have established its identity. For all you know it could be a cyanide, or a compound of thallium, cadmium or mercury.

That is a good point, CdS comes to mind when I see yellow although from several observations he has made I would not think so. Experimenting with a cyanide would not be good when one was unaware of the fact.

Oscilllator - 16-1-2015 at 18:26

Ok, more experiments have been done and the results are in:

-Once dissolved in HCl, the compound does not appear to react with metabisulphite, hydrolysed sucrose or thiosulphate, although the last is uncertain because of the formation of colloidal sulfur that could have obscured any reaction.

-There is no precipitate with the addition of potassium iodide to the compound once it is dissolved in HCl.

-A white precipitate is observed upon addition of the dissolved compound to a solution of sodium carbonate. No surprises there.

-Addition of the compound to a solution of copper sulphate resulted in a greener solution and the formation of a precipitate (see picture). I suspect the green colour is caused by the chloride ions coordinating to the Cu²⁺ ion.

-The compound does not appear to react with trichloroisocyanuric acid.

-A 50/50 mix of Aluminium powder and the compound was made, and I attempted to light it first with a propane lamp, then with a sparkler. The first did not succeed, but the second resulted in intermittent flashes as the sparkler burnt. However a control test with plain aluminium powder yielded the same flashes, so I don't think any reaction occurred.

-Now for the interesting one: Addition of aqueous potassium ferrocyanide to the solution resulted in an initial blue colour, followed by the formation of a dark green turbid solution over a period of ~30 seconds (see picture).

I think the ferrocyanide test should narrow it down considerably - thanks to The Volatile Chemist for that suggestion.
As always, any suggestions as to additional tests I could take are appreciated.

Random - 17-1-2015 at 09:31

Take this white precipitate and go on from there. It could be a mixture of stuff and it could damage analysis. White precipitate should be dissolved in acid again. Then check properties.

Also this will get rid of anion contamination because you aren't sure if anion is also reactive. Some anions can produce a mess and rhus interefere with cation analysis.

It could also be a jar full of mixed chemical waste.

[Edited on 17-1-2015 by Random]

The Volatile Chemist - 17-1-2015 at 12:33

"It could also be a jar full of mixed chemical waste."
That would be hilarious. So I assume you haven't done the ferrocyanide test yet? I'm looking forward to a picture. The permanganate solution could just be the formation of manganate ions.

Oscilllator - 17-1-2015 at 16:41

Quote: Originally posted by The Volatile Chemist

That would be hilarious. So I assume you haven't done the ferrocyanide test yet? I'm looking forward to a picture.

Errr...

That green stuff? Thats the picture.

I'll try isolating the white precipitate and analysing that. We'll see what we can get.

The Volatile Chemist - 18-1-2015 at 11:58

Quote: Originally posted by Oscilllator

Quote: Originally posted by The Volatile Chemist

That would be hilarious. So I assume you haven't done the ferrocyanide test yet? I'm looking forward to a picture.

Errr...

That green stuff? Thats the picture.

I'll try isolating the white precipitate and analysing that. We'll see what we can get.

Oh! Now we're getting someplace! The blue almost has to be Iron, likely oxidized to (III) since you used ferrocyanide, and not ferricyanide. The green color could be the Prussian blue (the blue stuff, if it was iron related) being turned into a cyanide of sorts because of whatever ion was attached to the compound, but I think not. I think it's either a mix of lots of metal ions all with the same cation (in short, someone's waste, 2nd most likely), or a single compound with iron impurities. The impurities caused the blue, and the actual metal ion caused the green. This would also make sense if the compound is a chloride, as HCl usually has Iron(III) impurities in it. I'd bet $10 on that last one, it fits the most evidence.

Oscilllator - 18-1-2015 at 15:55

I'll try adding plain ferrocyanide to my HCl to see if I get a blue colour. I'll also conduct more tests to see if the yellow colour is caused by the addition of HCl, and as well as that I'll conduct tests with the ferrocyanide on some known compound I have (FeSO4 being among them).

Perhaps isolating the precipitate from the addition of carbonate as Random suggested and testing that will yield some better results.

The Volatile Chemist - 18-1-2015 at 16:03

Quote: Originally posted by Oscilllator

I'll try adding plain ferrocyanide to my HCl to see if I get a blue colour. I'll also conduct more tests to see if the yellow colour is caused by the addition of HCl, and as well as that I'll conduct tests with the ferrocyanide on some known compound I have (FeSO4 being among them).

Perhaps isolating the precipitate from the addition of carbonate as Random suggested and testing that will yield some better results.

DON'T DO IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
That would produce HCN gas!!!!!!!!!!!!!!!
I'm kinda hoping you don't try it..............
Evaporate a sample of HCl, dilute residue, then add ferrocyanide.

Oscilllator - 18-1-2015 at 17:56

Quote: Originally posted by The Volatile Chemist

DON'T DO IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
That would produce HCN gas!!!!!!!!!!!!!!!

If I remember correctly from the cyanide preparation thread it shouldn't produce much cyanide gas unless heated, but your way sounds much safer so I'll do it that way.

The Volatile Chemist - 19-1-2015 at 14:34

Quote: Originally posted by Oscilllator

Quote: Originally posted by The Volatile Chemist

DON'T DO IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
That would produce HCN gas!!!!!!!!!!!!!!!

If I remember correctly from the cyanide preparation thread it shouldn't produce much cyanide gas unless heated, but your way sounds much safer so I'll do it that way.

Good. I'm curious as to what it will show.

sulfuric acid is the king - 16-4-2024 at 08:38

I needed some iron sulfate so i disolved scrap from scrapyard.
Few such metal sheet triangles (probably after some cutting process) disolved in 250ml Erlenmeyer gave such mass.
It broke my flask unfortunately when i tried to crush it with something.
It was insoluble even in boiling solution of iron sulfate/sulfuric acid.
So what can it be?

bnull - 16-4-2024 at 11:36

It's hard to say just by looking. I have some suggestions that may make it easier to identify the substance.

Could you please describe in details the procedure you employed? How did you get the grey pancake? Was it by boiling to dryness?
Could you try one or more of the following:
1. Dissolve a fragment in ammonium hydroxide;
2. Dissolve a fragment in a concentrated solution of sodium hydroxide;
3. Dissolve a fragment in hydrochloric acid;
4. Melt a fragment in a crucible.
If you still have some triangles left, could you please sandpaper one of them and test the powdered stuff as in (2)?

If I were to guess--and it's a very wild guess--, I'd say it is lead(IV) oxide, produced by the reaction of sulfuric acid and the dark paint on the surface of the triangle. It is very similar to one of those old rustproof primers based on lead(II,IV) oxide. When attacked by acids, lead(II) oxide is dissolved and lead(IV) remains, although in this instance the insoluble lead(II) sulfate would also deposit.

sulfuric acid is the king - 16-4-2024 at 12:28

I think it's definitely not from the paint beacause the quantity was much higher, and there was no paint on that steel as you can see, it's natural gray colour of the steel.
I just put 33 percent sulfuric acid and added that triangles, it was made in the process (gray cake), after everything cooled next day i had green crystals of iron sulfate, black stuff around (probably carbon from the steel) and that unsoluble cake at the bottom.
When i wash cake and add tap water (mine is chlorinated) interesting thing happens.
It seems that cake is slightly soluble. Water first becomes milky and then it gets red-yellowish colour, little bit like rust.
Also when i slowly shake it seems like i have 2 separate liquid layers, oily like at the bottom and that rusty above, but it's probably just density difference.
All this is from simple steel cuts, i don't think it's possible to make some alloy with such large proportion of lead in it, but i don't know really.
Thanks for suggestions i'll try some of them.

sulfuric acid is the king - 16-4-2024 at 13:44

That relatively unsoluble, white-grayish stuff from the picture above:

1.Few hours in tap water
2.Immidiate raction with 10% NaOH. (deep green precipitate)
3.Extremely slow reaction with 16% HCl. (it tends towards yellow-green)

So mistery compound is some iron hydroxide?
How can it be formed together with sulfate at the same time?
Interesting

bnull - 16-4-2024 at 15:14

Quote: Originally posted by sulfuric acid is the king

That relatively unsoluble, white-grayish stuff from the picture above:

1.Few hours in tap water
2.Immidiate raction with 10% NaOH. (deep green precipitate)
3.Extremely slow reaction with 16% HCl. (it tends towards yellow-green)

[...] Interesting

It is really interesting. It seems that the triangles were plain carbon steel; the orange smudges shown in the picture must be rust, so there was no lead paint. And iron doesn't alloy with lead. The cake seems to be a mixture of iron oxides and hydroxides, iron(II) sulfate, and maybe even iron powder^{Note 1}. This explains the partial solubility and the green precipitate in the reaction with NaOH.

Quote: Originally posted by sulfuric acid is the king

So mistery compound is some iron hydroxide?

Probably. If you add hypochlorite or hydrogen peroxide to the green precipitate, it will get brown or orange if it's iron(II) hydroxide. There's a table here that may help you confirm the identity: https://www.docbrown.info/page07/appendixtrans12.htm.

Quote: Originally posted by sulfuric acid is the king

How can it be formed together with sulfate at the same time?

Perhaps^{Note 2} by the sequence of reactions below:

Iron is dissolved by sulfuric acid:$$Fe(s)+2H^+(aq) \rightarrow Fe^{2+}(aq)+H_2(g)$$
It reacts with the air dissolved in the solution and is oxidised:$$4Fe^{2+}(aq)+O_2(aq)+4H^+(aq) \rightarrow 4Fe^{3+}(aq)+2H_2O(l)$$
The ferric ion attacks the solid metal:$$2Fe^{3+}(aq)+Fe(s) \rightarrow 3Fe^{2+}(aq)$$
If there's an excess of solid iron, as it seems the case, the metal that is attacked in step 3 will end up reacting with the oxygen dissolved and the water, forming oxides and hydroxides^{Note 3}:$$Fe^{2+}(aq)+O_2(aq)+H_2O(l) \rightarrow Fe(OH)_2(s)+Fe_2O_3(s)+FeO(OH)_2\cdot nH_2O(s)+other~stuff$$

The reactions stop when there is no more acid and oxygen to react with the iron.

Note 1: Maybe not exactly iron powder. Some iron carbide, silicon perhaps, iron phosphides/phosphates (I don't know which) maybe, and manganese carbide. Every carbon steel has some manganese in it.
Note 2: The electrochemical potentials are favorable.
Note 3: The equation is unbalanced because the composition is unknown. Well, at least unknown to me.

sulfuric acid is the king - 17-4-2024 at 07:27

Quote: Originally posted by bnull

If you add hypochlorite or hydrogen peroxide to the green precipitate, it will get brown or orange if it's iron(II) hydroxide. There's a table here that may help you confirm the identity: https://www.docbrown.info/page07/appendixtrans12.htm.

And exactly that happened, mistery solved, thanks