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Author: Subject: Mercury Oxides

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[*] posted on 3-5-2005 at 21:17
Mercury Oxides

What is the difference between red & yellow mercury oxide? (both being HgO).

Im looking to synth them, presumably an oxide can be produced from mercury by dissolving it in HNO3, then precipitating with hot NaOH? Which oxide forms?

Is this the best way to go about it from mercury. I can buy the oxide but I have a lot of mercury and the oxide is very expensive!

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[*] posted on 3-5-2005 at 21:45

IIRC, they are two different crystalline modifications of mercuric oxide.

I would be very wary of pouring hot NaOH on nitric acid.

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[*] posted on 3-5-2005 at 21:47

Originally posted by sparkgap
I would be very wary of pouring hot NaOH on nitric acid.

Well... Of course he would seperate mercury nitrate from the acid solution first before dissolving it in distilled water and precipitating with NaOH :D

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[*] posted on 3-5-2005 at 21:49

When I did my 'research' on producing mercuric oxide I found that it is best prepared by adding sodium carbonate to a soluble mercury salt. This worked well for me and gave me a nice red/orange powder.

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[*] posted on 4-5-2005 at 02:51

NaOH has the advantage of no gas evolution and therefore no toxic spray droplets.
The problem would be the strong heat evolution, but this can be overcome by diluting both solutions.
The nitric doesn't have to be removed first, because the sodium nitrate stays in solution.

I haven't tried to make HgO, but someone told me that he had tried it and the addition of NaOH to the Hg(NO3)2 / HNO3 solution caused the red modification to precipitate. This is strange because precipitations nearly always produce the yellow modification.
The yellow HgO is finely divided and has some lattice distortions (and thus higher reactivity: it reacts faster with acids such as HCl). The red modification is produced by carefully heating the yellow modification.
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[*] posted on 7-5-2005 at 06:20

Concentrated H2SO4 also does a good job dissolving elemental Mercury. It has to be heated for the mercury to dissolve, forming the sulphate. You can use this to prepare the oxide intead of the nitrate. There´s a write-up for this around somewhere (Rhodium?).
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[*] posted on 1-7-2005 at 08:52

just a note, all these mercury compounds are light sensative so just dont leave them out in the sunlight for a long period. (the nitrate i dont think is light sensitive)
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[*] posted on 3-9-2006 at 07:50

I hope no one minds me bring this thread back up but I was wondering if there is a consensus on the most efficient method of making HgO ? I was going to do some experiments and I see no need to buy it as I have a great deal of the metal available.


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[*] posted on 3-9-2006 at 08:16

Efficient huh ? This has been covered before .

Dissolve mercury in a slight excess of concentrated
nitric acid , using good ventilation and avoiding the
deadly fumes of nitrogen oxides , to form a solution
of mercuric nitrate . Evaporate the solution in a
glass bowl heated by a boiling water bath , to a solid residue of mercuric nitrate, with heating continued
further for several hours which decomposes the solid
nitrate to the oxide . Occasional stir the solid residue with a glass rod to break it into a loose powder
to allow for quicker escape of entrapped NO2 , and
" airing out " of the fumes from the residual oxide .
These fumes from the decomposition of the solid nitrate
should also be avoided as they are deadly toxic and
should be regarded with the same respect as cyanide ....
no exaggeration here .

This process is efficient , but just as lethal for anyone
who gets careless will just as efficiently end all
their troubles too .

The light yellow-white form is produced by this method .
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[*] posted on 6-10-2012 at 07:22

Interestingly, one may wish to keep their concentrated nitric acid and test out the following procedure. To form a soluble Hg salt, try using plain old bleach (NaOCl with NaCl), KCl and a little vinegar (Acetic acid) to form some Hypochlorous acid. Reaction:

NaOCl + HOAc --> NaOAc + HOCl

A source is, to quote, (see Introduction at "Mercury absorption in aqueous hypochlorite" by Lynn L. Zhao, and Gary T. Rochelle, link: ):

"Solutions of hypochlorite are known to dissolve mercury. Parks and Baker (1969) described the recovery of mercury by contacting mercury containing material with a hypochlorite solution maintained at a pH of 4.5 to 9.5"

Also, "They concluded that hypochlorous acid was much more reactive than hypochlorite. With hypochlorite, reactivity further increased in the presence of sodium or potassium chloride. Potassium hypochlorite was more reactive than sodium hypochlorite."

The above article does not address the chemistry. However, it has been in Watt's "A dictionary of chemistry and the allied branches of other sciences", Vol 8, p. 449, link: ). To quote:

"Detection and Estimation of hypochlorous acid in presence of Chlorine, Chlorous acid, and Chloric acid.—Free hypochlorous acid agitated with metallic mercury converts it into mercuric oxychlonde, Hg2Cl2O or HgCl2.HgO, whereas free chlorine converts mercury into mercurous chloride, Hg2Cl2. Consequently, hypochlorous acid mixed with chlorine may be easily detected by the more yellowish colour produced on (halting it with mercury, unless its quantity is very small in comparison with the free chlorine. In the latter case it is necessary to decompose the oxychloride with hydrochloric acid, filter, and agitate the filtrate with mercury. If the hypochlorous acid is in combination with bases, its detection is even easier than in the free state: for in this case, agitation with mercury gives rise to the yellow oxide, easily recognised by its colour, and by its property of sticking to the sides of the glass vessel on agitation : KClO + Hg = HgO + KCl. Chlorous and chloric acids when combined with bases do not act upon mercury (Wolters, J. pr. Chem. [2], vii. 468)."

Also, "These reactions may be made the basis of a quantitative estimation of hypochlorous acid in presence of free chlorine, chlorites, and chlorates, in as much as by brisk agitation with excess of mercury, the whole of the hypochlorous acid and its salts may be decomposed in about five minutes. The mercuric oxide formed in the reaction is easily dissolved by hydrochloric acid; the mercury contained in the filtrate may be precipitated as mercurous chloride by ferrous salt and an alkali;"

I would then add NaOH (or possibly Na2CO3) to recover HgO per the reaction cited per Watt's for KClO:

NaClO + Hg --NaOH--> HgO (s) + NaCl

and/or with Hypochlorous acid:

HOCl + Hg + NaOH --> HgO (s) + NaCl + H2O

[EDIT] Please note that Mercuric acetate, chloride and oxide are on Wikipedia list of list of extremely hazardous substances defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002). Link:

[Edited on 7-10-2012 by AJKOER]
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