Sciencemadness Discussion Board - unknown substance

unknown substance

CharlisonX - 23-11-2016 at 09:41

Hello, Sciencemadness! I am Charlison, a long-time lurker of this forum(~2 years) and small-time chemist, amongst other hobbies.
I finally decided to create an account for a question i had for a long time ago.
this '?' labeled dust is a pure lab reagent, i forgot which one.

what i know is that i got him together with sulphuric acid, nitric acid, potassium iodide, NaOH pellets,metallic iodine and sodium sulphate.
it's not lead nitrate, my teacher didn't let me touch that one

how can i know what is this dust?

0747fb60-72e7-47d6-92de-64b383ff6b49.jpg - 84kB

Maroboduus - 23-11-2016 at 10:15

Go get, or download, a Quantitative analysis textbook.

Read it.

Buy the reagents they use.

Do what they tell you to do.

Alternatively you can try and find some lab to analyze it for you at a reasonable fee. Or it may be easier to try and find some lab to analyze it for you for a hefty fee.

TheMrbunGee - 23-11-2016 at 11:02

You need to do some tests, I assume you will not get and read Quantitative analysis textbook.

As I understood - it is one of "sulphuric acid, nitric acid, potassium iodide, NaOH pellets, metallic iodine and sodium sulphate" correct?

sulphuric acid, nitric acid - liquids, so no.

NaOH pellets - not dust so - no!

"Metallic" iodine I think you mean crystalline, but it is dark colored, so no!

So it is either sodium sulphate or potassium iodide?

Easy test is to try dissolving it! If you can dissolve 10 g of it in ~50 ml fridge temperature water - then it is Iodide, if you can’t - it is sulphate!

aga - 23-11-2016 at 11:26

Put a tiny amount on a spoon and tip the dust into a flame.

See what colour it makes.

CharlisonX - 23-11-2016 at 11:54

i did try dissoluting it, it is lighter than water, and it didn't reacted until i mixed manually. it's heavier than 98% ethanol tho, and soluble on the latter, i don't have a scale so i can't say how much.

also, i put it in the spoon and pointed a flame, besides the blue color of the flame, i didn't saw any particular color, i mean, the dust started glowing bright yellow, so maybe that caused some interference

EDIT: i'll point out that i think it's talc, and if it is, i'll be so disappointed that i'll make sure the sample never existed
also, i have matters to attend later so i can't do any experiments after a hour or two from now

[Edited on 23-11-2016 by CharlisonX]

Maroboduus - 23-11-2016 at 12:06

Quote: Originally posted by TheMrbunGee

You need to do some tests, I assume you will not get and read Quantitative analysis textbook.

As I understood - it is one of "sulphuric acid, nitric acid, potassium iodide, NaOH pellets, metallic iodine and sodium sulphate" correct?

sulphuric acid, nitric acid - liquids, so no.

NaOH pellets - not dust so - no!

"Metallic" iodine I think you mean crystalline, but it is dark colored, so no!

So it is either sodium sulphate or potassium iodide?

Easy test is to try dissolving it! If you can dissolve 10 g of it in ~50 ml fridge temperature water - then it is Iodide, if you can’t - it is sulphate!

If it is in fact one of those chemicals then you're certainly right.

It was my impression from his post that he was telling us he bought this along with those other chemicals, and that he had no idea what it is.

Can't imagine why he wouldn't say it's one of those chemicals if it is, in fact, one of those chemicals. However the only other bit of information he gave us is that it's NOT lead nitrate. Why would he point out it isn't lead nitrate if he's telling us it's one of those other chemicals?

aga - 23-11-2016 at 12:12

Heigh-ho. Best of luck with it then.

Some Qualitative analysis might be easier to get started with.

Maroboduus - 23-11-2016 at 12:13

Quote: Originally posted by CharlisonX

i did try dissoluting it, it is lighter than water, and it didn't reacted until i mixed manually. it's heavier than 98% ethanol tho, and soluble on the latter, i don't have a scale so i can't say how much.

also, i put it in the spoon and pointed a flame, besides the blue color of the flame, i didn't saw any particular color, i mean, the dust started glowing bright yellow, so maybe that caused some interference

EDIT: i'll point out that i think it's talc, and if it is, i'll be so disappointed that i'll make sure the sample never existed
also, i have matters to attend later so i can't do any experiments after a hour or two from now

[Edited on 23-11-2016 by CharlisonX]

Talc is much higher in density than water, and is not soluble in water or ethanol. This should be good news, as it will relieve you of the necessity of making sure the sample never existed.

CharlisonX - 23-11-2016 at 12:17

oddly, the alcohol-? solution went grey in the meantime

CharlisonX - 23-11-2016 at 12:30

i'm leaving now, as an extra i'll leave my last two tests:

added silver nitrate on the two solutions: no change
added '?' on vinegar: insoluble, no reaction

TheMrbunGee - 24-11-2016 at 06:18

Quote: Originally posted by CharlisonX

It is probably floating in top of water because it is fine powder and there is air trapped within the pile.
So it is soluble in water? Is the solution clear and colorless?

Talc will react with strong acids.

Quote:

oddly, the alcohol-? solution went grey in the meantime

Did the powder just sank to the bottom? Alcohol might have extracted some impurities from the powder if so!

Bert - 24-11-2016 at 07:30

Potassium iodide is soluble in methanol, and PROBABLY in ethanol. Your sample dissolved in alcohol?

Take a few ml of alcohol, dissolve as much chemical as will easily do so in it. Ignite the solution on a CLEAN surface. Does it have a lilac/lavender colored flame (Potassium spectrum).

https://youtu.be/jJvS4uc4TbU

[Edited on 24-11-2016 by Bert]

NitratedKittens - 29-11-2016 at 02:31

The only thing about potassium flame test is that it is very easily contaminated with other compounds, However if it is a pure reagent, and it has been stored properly then it should work.

Texium - 29-11-2016 at 06:21

There was no precipitate with silver nitrate. Potassium iodide has already been disqualified by that test. Plus he said from the start that he got it with KI, not that it could be KI.

I'm wondering if it's an organic compound, perhaps a sugar. Try adding a drop of conc. sulfuric acid to a pile of it, carefully, and see if it carbonizes.

Otherwise, just test an aqueous solution of it using a bunch of different qualitative tests if you have the materials. See if you get a precipitate with chloride, sulfate, carbonate, barium nitrate, etc. See if it will reduce a dichromate or permanganate solution.

NitratedKittens - 29-11-2016 at 12:30

Get some distilled water, and dissolve the substance then test for electrical conductivity, if it is ionic it will disassociate and start conducting electricity. if it is covalent the conductivity will not change.

CharlisonX - 4-12-2016 at 09:49

Quote:

I'm wondering if it's an organic compound, perhaps a sugar. Try adding a drop of conc. sulfuric acid to a pile of it, carefully, and see if it carbonizes

i added a drop of sulfuric, but there was no reaction,
I suspect my acid absorbed atmospheric water, as i tested it with regular sugar and didn't carbonized. too

Quote:

Otherwise, just test an aqueous solution of it using a bunch of different qualitative tests if you have the materials. See if you get a precipitate with chloride, sulfate, carbonate, barium nitrate, etc. See if it will reduce a dichromate or permanganate solution.

ferric chloride: no precipitate
sodium carbonate: no precipitate
copper sulfate: it seemed the compound flaked but I tried again with a new sample after the insoluble part went to the bottom. no precipitate
barium nitrate: I don't have BaNO3, but I tried with silver nitrate: no precipitate
potassium permanganate: no reduction, at least not any bubbles or precipitate,
(my pernanganate is part reduced to MnO2, but it still can draw oxygen from H2O2)
sodium hydroxide: no precipitate
i also felt all mixtures, there wasn't any significant change of temperature at all

Quote:

Get some distilled water, and dissolve the substance then test for electrical conductivity, if it is ionic it will disassociate and start conducting electricity. if it is covalent the conductivity will not change.

i don't have distilled water, but I have a multimeter, and I made some tests:
tap water: 115k ohms
tap water with '?': 200k ohms
tap water with table salt:12k ohms
tap water with sulfuric acid: 0,8k ohms
i also apologize for almost necroing the thread, but my laptop died when i tried to open it later that day, fixed it today.

phlogiston - 5-12-2016 at 07:13

If it was organic, very likely you would have observed it decomposing and/or melting when you heated it directly in a flame. However:

Quote:

also, i put it in the spoon and pointed a flame, besides the blue color of the flame, i didn't saw any particular color, i mean, the dust started glowing bright yellow, so maybe that caused some interference

With 'glowing bright yellow', do you mean you saw the powder sitting there on the spoon emitting a yellow glow, or do you mean the flame itself turned yellow, possible from vapor from the powder or particles being blown into the flame?

NitratedKittens - 6-12-2016 at 00:02

also, did some sooty smoke come from the compound when heated.

CharlisonX - 6-12-2016 at 04:36

No. It was the powder that was glowing, like a piece of charcoal. It cooled very fast when I stopped heating,
No soot either, the dust was as white as packed.
Except for some dark in the vicinity of the flame(probably from the butane flame itself, i didnt pointed at those areas)

Harristotle - 6-12-2016 at 06:37

Titanium dioxide powder glows yellow when it is heated up, and loses it when it is cold.
Test by adding 0.5g to 5ml conc sulfuric and heat until fumes are formed. Dilute to 100ml, then add 6% H2SO4. Should turn orange-red if TiO2.

phlogiston - 6-12-2016 at 07:34

So, it is likely to be an inorganic compound.

What is puzzling is that it dissolves in ethanol, but not in water.

TiO2 nor any other metal oxide I can think of has that property.