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Author: Subject: Mercury Oxidation - Prevention
Gooferking Science
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[*] posted on 16-11-2014 at 09:45
Mercury Oxidation - Prevention


I like my mercury nice and shiny. Recently I noticed that my mercury had lost its shine due to oxidation. I filtered it with a small hole poked in a coffee filter, and it is back to its normal shininess. Unfortunately, some of the mercury is lost in the mercury oxide... Any good ways to prevent oxidation? Would vacuum sealing in an ampoule be my best bet? What is the best way to do that?



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S.C. Wack
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[*] posted on 16-11-2014 at 10:32


It cannot oxidize in the absence of air, and there isn't much O (or S) inside most containers. It doesn't form an oxide in air anyways. Check the properties of the oxides. If you heat the scum you probably will get free Hg vapor, but I'm going to doubt a HgO residue.

Perhaps your Hg is less pure than you think.

Oxidizers like KMnO4 and HNO3 might help in fact.




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HgDinis25
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[*] posted on 16-11-2014 at 10:56


Mercury isn't oxidized by air in regular conditions. And even if it was, Mercury (II) Oxide is an orange powder. There's also a Mercury (I) Oxide wich is unstable.

Perhaps your Mercury has amalgamated with a metal? In those situations Mercury creates a "scum" of blackish solids that float on top of the liquid Mercury.
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[*] posted on 16-11-2014 at 11:52


A few years ago I purchased a large amount of mercury as part of my experiments into fulminurates and related heterocyclics. The mercury was very very old probably dating from the early 1900's or even Victorian times; some of the ceramic jars still had their original wax seals over the corks while others had been opened and partly used. Those that had not been opened contained mercury that was bright and clean while some of those that only had a little mercury left in them had a copious black powdery scum. I found that the scum is partly soluble in dilute nitric acid (4:1 so about 14%) but the remaining black powder was very inert even towards conc nitric acid (68-70%) and even hot nitric acid dissolved it slowly. However, this powder gives a positive reaction to the iodide-iodine-azide reaction (brown to colourless+effervecence) indicating that the insoluble material is mainly a sulphide. Low temperature precipitation of mercury sulphide with H2S also gives a black ppt of the metastable cubic form of mercuric sulphide, the stable red trigonal form (cinnabar or vermilion) is produced by heating or grinding mercury and sulphur together dry.

So, since the black scum is partially soluble in dilute nitric acid and partially not I suspect that it is a mixture of oxides and sulphides of mercury; interestingly the dilute nitric acid solution contains both mercuric and mercurous ions.
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[*] posted on 16-11-2014 at 12:11


Hm, I don't have any metal in the ampoule I keep it in. The mercury must be reacting with something in the ampoule. I got my mercury from taking apart thermostat switches, so it might have some impurities in it. Running some tests on the junk would be the best thing to do now.



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HgDinis25
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[*] posted on 16-11-2014 at 12:45


Quote: Originally posted by Gooferking Science  
Hm, I don't have any metal in the ampoule I keep it in. The mercury must be reacting with something in the ampoule. I got my mercury from taking apart thermostat switches, so it might have some impurities in it. Running some tests on the junk would be the best thing to do now.


Careful with what you do. Most tests envolve conversion of Mercury metal to soluble inorganic species (Hg2+ or Hg+ usually). Although inorganic Mercury doesn't cross the blood-brain barrier easily, it is a heavy metal and has a very high acute toxicity. A few mg of it and you'll be in the fast track to kill your kidneys and other useful body organs.

And how do you keep it in an ampoule? An ampoule is something you have to break to get whatever is inside. I'm assuming you keep it in some sort of vial or bottle. Is the vial air proof? Do you keep it near other reagents? Wich ones? Have you performed reactions that may have liberated gases or fumes near it?

[Edited on 16-11-2014 by HgDinis25]
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[*] posted on 16-11-2014 at 13:31


Didn't they use to purify Hg by running it bit by bit through a column of dilute nitric acid?



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[*] posted on 16-11-2014 at 15:32


Quote: Originally posted by blogfast25  
Didn't they use to purify Hg by running it bit by bit through a column of dilute nitric acid?


Who's they? There are a few methods employed in industry that indeed use Nitric Acid. An example:
http://www.google.com/patents/US3364128
However, if good quality Mercury is needed, the industry usually just distills it. It's cheaper than using Nitric Acid and having to dispose of Inorganic Mercury salts (Mercury always reacts a little bit with Nitric Acid regardless of concentration) is expensive.

The best way to purify dirty Mercury is distillation. If you don't have the necessary equipment, putting some cotton in a syringe and forcing the Mercury through it usually works.

[Edited on 16-11-2014 by HgDinis25]
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S.C. Wack
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[*] posted on 16-11-2014 at 18:43


Note that one of Brauer's purifications is air blown/sucked through mercury with aspirator vacuum (under sulfuric acid).

Quote: Originally posted by HgDinis25  
(Mercury always reacts a little bit with Nitric Acid regardless of concentration)


I didn't find evidence of this, even when shaken (~ the bejeezus out of) with Hg in a form that is somehow both powder and gel.
https://www.sciencemadness.org/whisper/viewthread.php?tid=10...




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[*] posted on 16-11-2014 at 22:17


I think a redistillation would clean it up. there is bound to be all sorts of amalgamated rubbish in there.
mine does the same, but I suspect it is rubbish and intend to distil
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[*] posted on 17-11-2014 at 13:05


S.C. Wack, you refered me to a post where you talk about shaking Mercury with cold Nitric Acid. Seeing what you wrote there made me think that you misunderstood me.
The reaction between cold dilute Nitric Acid and Mercury is slow but it is there and it happens. Of course that shaking it for 5 minutes isn't going to diminish your mass of Mercury metal by much. What I was saying is that, if done in industry, such method produces small quantities of Mercury(I). This needs to be disposed of so more money is lost paying the disposal companies.
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[*] posted on 17-11-2014 at 14:33


There was no misunderstanding. The HNO3 that washed several hundred grams of Hg dissolved none at all to milligrams. It obviously dissolves at some point, but not a point that I'm aware of. Vogel: "Used mercury should be washed with water, thoroughly agitated for about 12 hours in contact with 10 per cent nitric acid..."

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Quote: Originally posted by blogfast25  
Didn't they use to purify Hg by running it bit by bit through a column of dilute nitric acid?

There's a few takes on this.
J. Chem. Educ., 1978, 55 (11), p 734
http://dx.doi.org/10.1021/ed055p734
...An alternate procedure developed in our laboratory is to pretreat the mercury by a flotation technique and then to slowly pour the mercury through a glass column containing glass beads and 8 M nitric acid. Dirt or similar material in the mercury is removed by placing the mercury in a side arm flask in a plastic tub and flushing the surface of the mercury with running water. The mercury is then poured through a glass column which should not he filled more than two thirds full with glass beads and acid. Space must be left in the column for the solution to expand should any reaction occur. As the mercury strikes the glass heads, it disperses into small droplets which present a large surface area for reaction with the nitric acid. The mercury is then poured through a similar column containing glass beads and distilled water. The acid-distilled water wash procedure is repeated three times. changing the nitric acid and the distilled water after each cycle. If the mercury needs to be degreased prior to the acid distilled water cycle, a glass column containing glass beads can he set up using an appropriate organic solvent, followed by a distilled water wash step.

The wet mercury can be dried by careful heating in a porcelain dish on a hot plate at low heat (HOOD). If the temperature is too high, the mercury will first form an oxide film and then vaporize; therefore, the hot plate must he just warm enough to drive off moisture and not any warmer. Formation of surface scum at this stage is an indication of residual contamination.

As crude as it may seem, the appearance of the surface can often he used as a rough gauge of the purity of the mercury. The presence of base metals to a concentration of 1 part in 10 million of mercury can be detected by the loss of the mirror-like appearance. Although the lower limit of base metal impurities which can he achieved by washing with nitric acid is uncertain, it is thought to be less than 1 ppm. Noble metals will not he eliminated by the nitric acid wash procedure, and they must be removed by distillation if their presence is troublesome.

The whole cleaning procedure should he performed in a hood (especially the acid wash and heating steps) with precautions taken against spills. This procedure is not only fast and simple, but it also yields mercury that is reasonably clean.




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[*] posted on 18-11-2014 at 01:42


Yeah. I had the same problem with my mercury. I washed it with dilute nitric acid several times, filtered through a pinhole and it still gets s scum on top on prolonged storage in air. I solved the problem by ampouling under argon.

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