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j_sum1
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[*] posted on 31-7-2017 at 21:16
Discoloration of stannous chloride


I have been cleaning up some old stock solutions in my school lab and have come across some stannous chloride solutions that are quite discoloured. I am used to SnCl2 being an off-white but this is something different.

The first solution was actually one I prepared myself about a year ago by dissolving some tin pellets in HCl. It has been stored in a PE dropper bottle for over that time. It is now a bright yellow colour.

The second is in a glass reagent bottle dating back at least ten years. It seems someone inexpertly attempted to dissolve SnCl2 in neutral distilled water. There is a thick white sludge on the bottom of the bottle. Stirring it up reveals some pale yellow discoloration. There are also some greenish lumps in the very bottom of the sludge which I assume originate from the bottle not having been properly cleaned.

Anyway, I am curious as to what the yellow colour is. My intention is to purify and recycle if possible. there is quite a bit there.

Actually, advice on purification would be welcome too. I am predicting that it will be a bit of a dog to work with.

[Edited on 1-8-2017 by j_sum1]
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[*] posted on 31-7-2017 at 23:25


Could the yellow precipitate be insoluble lead stannate, Pb2SnO4, due to lead (plus O2 from air) contamination ?
https://en.wikipedia.org/wiki/Lead-tin-yellow




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[*] posted on 1-8-2017 at 02:51


Quote: Originally posted by Sulaiman  
Could the yellow precipitate be insoluble lead stannate, Pb2SnO4, due to lead (plus O2 from air) contamination ?
https://en.wikipedia.org/wiki/Lead-tin-yellow

Lead contamination in the reagents used? Maybe. I'll check the source of the tin metal tomorrow. I have since mixed the two samples together but I can test for lead -- I think. Ill have to work out a way of detecting trace lead and differentiating it from the tin.

It is likely that the sludge came from the one of the (very old) bottles of SnCl2 we have on the shelf. One is the dihydrate and the other anhydrous. One might have an assay on it but the other is pre-metric and poorly labelled.

It's nice to have a little puzzle.

I will see if I can test the solution for lead.
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[*] posted on 1-8-2017 at 20:03


Update.

All three sources of tin -- the granules I used, the SnCl2 and the SnCl2.2H2O te technical grade. Which means that lead contamination is reasonably likely.

The 1 year old solution prepared from metal dissolved in HCl was a yellow solution with no precipitate. It was quite strongly coloured. I can't figure out what this is yet. I am picking that Sn is in the +4 state as a stannate as a result of available oxygen but then it should precipitate if lead is present. It certainly had sufficient time to settle out and so I am not thinking of fine particulate material.


I combined the two mixtures, partially boiled it down to get rid of water and left it to settle. What remains is a cream-yellow fine powder and a slightly cloudy yellowish liquor. The liquid is highly acidic. It tests positive for chloride with AgNO3 (hardly surprising) and negative for sulfates with Ba(NO3)2.

Testing with potassium iodide causes a deeper yellowing but no precipitate. This could easily be lead iodide at low concentrations. I am not seeing any red/orange precipitate of tin(II) iodide.

Neutralising with NaOH gives interesting results. Cloudiness begins to appear at around pH 4. By the time it becomes alkaline the cloudiness disappears and is replaced by a grey-green flocculant material. This resembles the greenish lumps that appeared in the sludge.
On filtering it separates into a yellow precipitate (Pb2SnO4? PBO?) and a small amount of grey material that settles last. The filtrate does not appear to contain any lead when tested with a carbonate solution.

I would be tempted to think the grey material is metallic except that it was the last to settle in the filter paper. It looks pretty dark. It is also extremely fine. Tin and lead convert from 2+ to elemental at almost the same reduction potential and so if it is metallic it could be both. I am not picking what would have done the reduction though. Perhaps I am missing something obvious.

Returning to the original liquor, I have carefully adjusted the pH to 6 using NaOH. A white precipitate is slowly settling out. At least I think it is white. It is a bit hard to tell in the presence of universal indicator. I intend to test the liquid portion with carbonate. If any lead remains then it should be visible.


I think the conclusion is that Pb is likely in my original reagents and that I have a bit to learn about distinguishing between tin and lead.
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[*] posted on 2-8-2017 at 05:06
Ammonium thiocyanate test colors


It is known that a qualitative test for iron ions (Fe+3) is the blood red color they form with a thiocyanate ( link )

Do you know any other metal that forms the same blood red color when reacted with a thiocyanate? (e.g. heavy metals, precious metals?)


I see this blood red color when adding thiocyanate in an Au chloride solution (Au was of .999 purity). Does this mean that the Au is contaminated with iron?

(the acids used were tested and found to be free of iron)
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[*] posted on 2-8-2017 at 12:56


I recently purchased a Corning PC220 hot plate stirrer off eBay. The stirring functions normally, but when I turn the heating on it makes a loudish buzzing noise when starting up. This noise subsides as the unit warms up. Is this anything I should worry about? I did remove the ceramic top before powering it on to clean out some accumulated dust.
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[*] posted on 3-8-2017 at 03:59
Question and Answer


I recently received 5 kg of cobalt (II) sulfate heptahydrate as a gift. Any ideas for interesting things to do with it? I'm not too keen on messing around with heavy metal salts (cumulative toxicity makes me nervous), but this seems like too large a quantity to ignore if there is anything worth doing with it.

Edit: Cryolite, I wouldn't worry too much about the buzzing unless parts other the ones that are supposed to are heating up. The oscillating magnetic field induced by the alternating current can cause slight vibrations in the conductors/resistors that result in audible frequencies.

[Edited on 3-8-2017 by agent_entropy]

[Edited on 3-8-2017 by agent_entropy]
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[*] posted on 3-8-2017 at 04:49


Cobalt chemistry is fascinating -- lots of complexes and interesting colours and a couple of oxidation states. But 5kg is a lot to play with. More than you would need. If it was me I would keep 500g and barter the rest.
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[*] posted on 6-8-2017 at 00:44
Does water aspirator flow rate affect max vacuum, or only the rate the vacuum is pulled?


Googled, didn't see anyone else asking this. I understand that the maximum vacuum is related to the vapor pressure of the liquid at the given temperature, but does the flow rate of the liquid have an effect on the vacuum?
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[*] posted on 6-8-2017 at 03:34


Yes it does, you need the pressure to push the flow to 5gpm for mine any ways it is the brass one sold from deschem.
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biggrin.gif posted on 9-8-2017 at 10:45
Making esters from butyric acid


In the spirit of making odors by combining carboxylic acids (ie propanoic acid) and alcohols (ie ethanol) with a drop of sulfuric acid, is the following combination safe to mix:
Butyric acid (abt 10 drops)
Octanol (abot 10 drops)
Sulfuric acid
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[*] posted on 9-8-2017 at 10:51


Yes



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[*] posted on 11-8-2017 at 01:29
Making benzyl alc from polystyrene


I thought I might try producing benzyl alcohol from polystyrene just for fun.

To accomplish this, I was thinking:

Step 1. Depolymerize polystyrene to give styrene, this can be done by distilling the polystyrene. Use immediately in step 2 to prevent repolymerization

step 2. Reflux styrene with dilute sulfuric acid solution and sulphur (inhibits the polymerization of styrene). The styrene should undergo addition with water to produce the benzyl alcohol.

step 3 isolate the benzyl alcohol

Sound potentually feasible?





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[*] posted on 11-8-2017 at 03:27


Hydration of styrene would typically result in 1-phenylethanol. You'd have to demethylate it somehow.



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[*] posted on 11-8-2017 at 13:09


Thank for the respones.

Oh yeah your right, forgot about markovnikov's rule. 1-phenylethanol would be the major product, and phenethyl alcohol the minor.

1-phenylethanol is a secondary alcohol and should be easily oxidized to give the corrosponding ketone, Acetophenone! which is very useful. This is even cooler then making benzyl alcohol:).

Polystyrene could be a very cheap source of acetophenone.

I don't know much about hydration reactions in practice. Is a reflux with water and a bit of sulphuric acid enough to hydrate an alkene?




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[*] posted on 11-8-2017 at 15:34


So I made some isopropyl bromide (9.0g total). My next planned step is to try to see if I can alkylate salicylic acid with it.

I have 2 options for reaction conditions- anh. K2CO3 in butanone (never bothered getting acetone- but I might for this rxn) or I could try lithium isopropoxide in isopropanol, similar to sodium methoxide in methanol: the pKa's arent wildly different, and I have a lot of IPA. I could also try magnesium methoxide in methanol, lithium methoxide, or magnesium isopropoxide. I would rather not use methanol, as I am running low but I could always buy more.

Which is better? The pKa of salicylic acid's phenol is 13.6 so an alkoxide might be the better option. Or am I completely off-base here?




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[*] posted on 12-8-2017 at 03:41


Quote: Originally posted by Ramium  
Thank for the respones.

Oh yeah your right, forgot about markovnikov's rule. 1-phenylethanol would be the major product, and phenethyl alcohol the minor.

1-phenylethanol is a secondary alcohol and should be easily oxidized to give the corrosponding ketone, Acetophenone! which is very useful. This is even cooler then making benzyl alcohol:).

Polystyrene could be a very cheap source of acetophenone.

I don't know much about hydration reactions in practice. Is a reflux with water and a bit of sulphuric acid enough to hydrate an alkene?


I've never hydrated an alkene, but I think typically they use high temperatures and pressures to make the reaction proceed at a reasonable rate. It may be possible to do it by simply putting dilute sulfuric acid and styrene in a test tube, putting it in an iron pipe, sealing both ends, and heating the pipe in a metal bath; I don't know. Magpie could do it: http://www.sciencemadness.org/talk/viewthread.php?tid=14652




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[*] posted on 14-8-2017 at 10:22


Anyone know what the energy of a Cl=O double bond is?



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[*] posted on 16-8-2017 at 10:35


Is nickel resistant to HCl and H2SO4? I'm trying to find out if what I've ordered really is nickel... There was no reaction between it and hydrochloric acid (31%) but it was slowly reacting when I added 30% H2O2 (water turned green and there was strong smell of chlorine). With H2SO4 there was something to see (nickel turned dark gray but H2SO4 color hasn't changed and reaction was very slow).

Thanks!




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[*] posted on 16-8-2017 at 15:23


Quote: Originally posted by xfusion44  
Is nickel resistant to HCl and H2SO4? I'm trying to find out if what I've ordered really is nickel... There was no reaction between it and hydrochloric acid (31%) but it was slowly reacting when I added 30% H2O2 (water turned green and there was strong smell of chlorine). With H2SO4 there was something to see (nickel turned dark gray but H2SO4 color hasn't changed and reaction was very slow).

Thanks!


Yep, that's nickel. If you heat it to boiling in HCl it will react as well. Another way to identify it is using a magnet, it's one of the few ferromagnetic metals.. (Although I think it's weaker than iron?)




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[*] posted on 16-8-2017 at 16:38


Quote: Originally posted by Zephyr  
Quote: Originally posted by xfusion44  
Is nickel resistant to HCl and H2SO4? I'm trying to find out if what I've ordered really is nickel... There was no reaction between it and hydrochloric acid (31%) but it was slowly reacting when I added 30% H2O2 (water turned green and there was strong smell of chlorine). With H2SO4 there was something to see (nickel turned dark gray but H2SO4 color hasn't changed and reaction was very slow).

Thanks!


Yep, that's nickel. If you heat it to boiling in HCl it will react as well. Another way to identify it is using a magnet, it's one of the few ferromagnetic metals.. (Although I think it's weaker than iron?)


Thank you very much! Yes, it is attracted by a magnet. One more question: why the chlorine was produced when it reacted with HCl and H2O2? And at the same time the green color appeared - nickel chloride? But why chlorine and chloride at the same time? Or was it some other compound?




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[*] posted on 16-8-2017 at 17:41


Acidic solutions of H2O2 are strong enough to oxidize chloride into chlorine. The green color can be attributed mostly to dissolved chlorine, although I'll bet there's some nickel chloride in there as well. The HCl and H2O2 react to make chlorine and HCl reacts with the Ni to make NiCl2 (Edit: although the latter reaction should be pretty slow at room temp)

[Edited on 8/17/2017 by Geocachmaster]




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