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Polverone
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Mr. Anonymous: HgCl2 prep
Mercuric Chloride HgCl2 is a useful, although highly toxic material which may be easily made from metallic mercury. It is imperative this synthesis
be done outdoors because of extremely toxic fumes, or in a fume hood, or making some other arrangement for active ventilation which efficiently
carries away the quite deadly nitrogen dioxide fumes which are evolved at two stages in the synthesis of the precursor mercuric oxide. The mercury is
added to and dissolved in an excess of nitric acid density 1.42, and the mercuric nitrate solution produced is evaporated to dryness, decomposing the
unstable mercuric nitrate to form mercuric oxide. The mercuric oxide is then dissolved in a slight excess of the theoretical amount required of
concentrated HCl to form an acidic solution of mercuric chloride. The solution is evaporated to yield crystals of stable mercuric chloride.
Experimental :
50.2 grams of mercury is added to 75 ml of nitric acid in a 250 or 500ml flat bottom flask, and set aside for about two hours unattended for the
mercury to dissolve. Nitrogen dioxide is evolved from the mixture and the red fumes should be avoided because of the extreme toxicicity. The resulting
solution of meruric nitrate is poured in a shallow layer in a large glass bowl placed on a slightly boiling water bath, and the heated solution is
evaporated to dryness on the very slightly simmering water bath.
A crock pot with a removable liner is a utensil which I find is ideal for such evaporations. With the crock left uncovered the evaporation to dryness
of shallow solutions is easily done. Once a kitchen implement is used for processing toxic chemicals, it should never be used again for any food
handling because of toxic residues.
The dry hot mercuric nitrate residue is heated for an additional one hour with occasional stirring of the decomposing mercuric nitrate with a glass
rod until a yellowish white residue of mercuric oxide results. Red fumes of nitrogen dioxide are freely evolved during both the dissolving of the
mercury in the nitric acid and the subsequent decomposition of the mercuric nitrate, and these fumes are highly toxic. Avoid these fumes,
understanding that by "highly toxic", deadly is the accurate description of nitrogen dioxide. It is very bad stuff. Keep distant from the
reactions during the time when these dark red fumes are seen being evolved. To the dry residue of mercuric oxide is added 60 ml of 31.45 per cent HCl
and the bowl is swirled to form a clear solution of HgCl2. Some fumes from the excess HCl will be evolved from the hot solution and these should be
avoided also. The clear solution is again evaporated to dryness on the same slightly boiling hot water bath. The residue of mercuric chloride is
scraped from the bowl as much as possible using a plastic (not metal) spoon and stored in a properly labeled (Mercuric Chloride, HgCl2, POISON) glass
container with a plastic or glass cover. Use no metal lids and use no metal implements in contact with Mercuric Chloride. The slight residue which
cannot be scraped from the bowl can be rinsed from the glass with a small stream of methanol, into a small puddle on the bottom of the tilted bowl.
When the methanol evaporates the residue will be collected in a small area and this can be scraped from the bowl and added to the bulk of the mercuric
chloride which was scraped from the bowl earlier. Good technique should be practiced with mercury chloride because of its toxicity, keeping account
of every gram possible and avoiding its release into the environment. This ethic should apply to all mercury compounds but especially highly soluble
mercury salts like mercuric chloride. 67.95 grams would be 100 percent of theory, however the actual yield of 67 grams will be slightly less than the
theoretical yield, due to volatility and losses during manipulation.
Caution concerning metals:
On contact with many metals, the mercuric chloride or its solutions, is likely to amalgamate the metal and begin an active corrosive oxidation of the
metal, which will gradually reduce the metal to dust. Aluminum and magnesium are especially suceptible to attack and the rate of the oxidation is
such that the oxide forming from the metal can be seen extruding from the surface at a visible rate. The process can only be stopped by heating the
amalgamated metal hot enough to boil away the mercury from its surface, or to chemically arrest the process with something which reacts with the
mercury and converts it to a sulfide (in theory). Free sulfur, or sulfur dissolved in carbon disulfide, or sodium sulfide, or perhaps sodium
polysulfide may work to deactivate an amalgam. However I have not done experiments to confirm this countermeasure. If even a microscopic trace of the
amalgam remained as a residue, the corrosion would continue. Do not get mercuric chloride on anything made of aluminum which you wish to keep intact.
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Polverone
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response
This is handy for people who need HgCl2 and nothing else will do. But can't one also use Hg(NO3)2 or any other soluble mercury salt for
performing amalgamations? I also seem to recall from my good friend the Hive that one can form a mercuric iodide solution by placing metallic mercury
in an aqueous KI/I2 solution (tincture of iodine), avoiding fumes and acids altogether.
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madscientist
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Mr. Anonymous, sodium polysulfide should work for arresting the rapid oxidation process of reactive metals that mercuric salts initiate.
The fumes of mercury metal are toxic enough that I won't be found handling it without some ventilation.
Hg(NO<sub>3</sub> <sub>2</sub> surely could be used in
amalgamations, but it is quite soluble in water, which (I think) means it's more easily absorbed through the skin.
I looked up a few MSDS yesterday, and found that HgBr<sub>2</sub> is almost fifty times less toxic than HgCl<sub>2</sub>.
I'm postulating that's largely due to HgBr<sub>2</sub>'s significantly decreased water solubility. NaBr is easily found
OTC; it's sold as packets of powder in a cardboard box for increasing the bromine content in pools. So it may be a good idea to prepare
HgBr<sub>2</sub> rather than HgCl<sub>2</sub>...
Also, I suggest mixing solutions of NaCl (or NaBr) and Hg(NO<sub>3</sub><sub>2</sub>, then filtering out the precipitated HgCl<sub>2</sub> (or HgBr<sub>2</sub>, rather than converting the nitrate to oxide and then reacting with an aqueous
solution of the respective hydrogen halide.
[Edited on 7-4-2003 by madscientist]
I weep at the sight of flaming acetic anhydride.
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Polverone
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Mr. Anonymous: soluble mercury compounds
| Quote: | The nitrate of mercury is soluble but it is unstable, and it also reacts with ethanol. Its reactivity with ethanol is demonstrated in a fulminate
synthesis. Iodine is expensive and also watched.
So the more stable mercuric chloride is a better choice for amalgams. |
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chochu3
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One could also bubble an excess of chlorine (or any halogen) through mercury metal and get an a pure product after washing with sodium hydroxide.
First forming Hg2Cl2 then HgCl2 with the excess chlorine.
\"Abiding in the midst of ignorance, thinking themselves wise and learned, fools go aimlessly hither and thither, like blind led by the blind.\" -
Katha Upanishad
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mantis
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In dont think that Hg will react at room temperatures with chlorine.
But maybe..
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jon
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aqau regia does that in one fell swoop how about HCl and conc. H2O2 does that work? I once heard of this being done that way.
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chochu3
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I was going to ask the same question, since mercury will react with chlorine gas why not create it in-situ with Hydrochloric acid and peroxide. Will
this not work as gassing would?
Like your idea of precipitating HgBr2 from Hg(NO3)2 in aqueous solution. Sounds cleaner and faster. I might try this instead if no reply is giving
about the procedure above. Is their a certain concentration of nitric acid which must be used to prepare mercury II nitrate?
\"Abiding in the midst of ignorance, thinking themselves wise and learned, fools go aimlessly hither and thither, like blind led by the blind.\" -
Katha Upanishad
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Dr.Muto
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Hg&H2SO4=HgSO4//HgSO4&NaCl=HgCl2 I believe
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mantis
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you have to work with sublimating HgCl2 and that is not the best way.
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Flip
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This was on Rhodium, written by Zygoat:
| Quote: | [1] HgSO4
Measure 20g Hg and place in a 100ml conical flask. Do not use a round bottom flask, as all the mercury will not react. Add 60 ml concentrated H2SO4
(should be at least 94%) to the flask and fit a single hole stopper with a tube leading outside. This reaction produces lots of SO2 that will give you
chemically induced asthma if breathed. Now slowly heat the flask. Bubbles of SO2 will rise from the acid/mercury interface. Maintain a vigorous
bubbling of SO2 by adjusting the heat. A white crystalline deposit of HgSO4 will appear. The mercury should be completely reacted after about 30
minutes. Allow the reaction mixture to cool and pour off the acid. Pour the crystals/acid into 750 ml hot water and filter. Keep the liquid.
[2] HgCl2
Make up 500 ml saturated sodium(bi)carbonate solution. Add this to the HgSO4/acid solution in small quantities until effervesscence upon addition
stops and a red-brown percipitate forms. Filter off the percipitate. Add some more (bi)carbonate solution to the filtrate to ensure all the HgSO4 has
been reacted. Filter and repeat until no more red-brown percipitate forms. Wash percipitate with DH2O. Place in a 500 ml beaker and create a
suspension with 20 ml DH2O. Make up a solution of 20 ml strong hydrochloric acid in 100 ml DH2O. Add this to the suspension in small quantities with
good stirring. The solution will change from brown-red to yellow and finally a white curdy percipitate will be present in the liquid. Stop addition of
the HCl when the white percipitate appears. It is important that the solution pH should be near neutral as excess hydrochloric acid will prevent the
HgCl2 crystallizing in the next stage. Evaporate off most of the water either outside or fit a single hole stopper with a tube leading outside to vent
the steam away. Cool, filter the HgCl2 and dry. Yield 19.37g white crystals. For greater purity recrystallize from boiling DH2O.
Be very careful with HgCl2. Ingestion of 1/2 g has been known to be fatal. Don't heat in an open container above 300 C as it will volatise and end up
in your lungs. Always wear gloves when handling HgCl2 and its solutions. |
And coincidentally, this helps me a lot with something else i'm working on! Thanks for the reminder!!!!
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Zinc
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A little OT but can mercury be obtained by electrolysis of the solution of HgCl2?
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turd
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| Quote: |
Allow the reaction mixture to cool and pour off the acid. Pour the crystals/acid into 750 ml hot water and filter. Keep the liquid.
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If you do this, you will make an insoluble basic sulfate and filter it off, wasting perfectly fine Hg-salt.
I think when I worked with Hg(NO3)2 it gave the same problem - you can only ever completely dissolve it by dropwise addition of HNO3. That probably
doesn't make it the first choice for amalgamations. But it's possible that I'm thinking about the Hg(I)-salt.
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Maja
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I have one quick question ! Is "hydragyrum bichloratum" the as HgCl2 ? I assume that it's old name of it ,because I have seen KCl named "Kalium
chloratum" Thanks.
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woelen
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Probably you mean hydrargyrum bichloratum. Indeed this is HgCl2. It is a very old name, also used over here in the past. Most
confusing about those names is that the-atum extension does not refer to -ate, bit to -ide, so chloratum = chloride, and not chlorate!
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gobbles
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Zygoats HgCl2 prep: failure
I wanted some mercuric chloride, and followed Zygoat's procedure as listed above.
Adding water to HgSO4 does indeed produce an insol. yellow ppt. I wondered at this, but duly followed the procedure, filtering it, and adding bicarb.
to neutralize the clear and colorless solution. No red/brown ppt formed, but what I got instead was a bright yellow ppt. After filtering this and
washing with cold water, I created the suspension and added dilute HCL, to no effect. No white curdy ppt formed, no fizzing, no visible sign of
reaction. I checked the pH and it was a bit low (2), and at this point I stopped, sealed everything up, and called it quits.
Now I would like to know is, what have I got, and can I make it to the chloride? The only two yellow mercury compounds I could find in the lit. were
yellow mercuric oxide and mercuric subsulfate. Is there any reasonable way to procede?
Oh, I'm new here, so hello. Sorry for bringing up an old post. Don't worry everybody, no waste of mine is going down the drain.
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Magpie
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Is your resulting solution clear or translucent yellow? If so maybe what you have is a solution of HgCl2. That is what I made using Mr Anonymous'
procedure. This was then carefully evaporated to get the pure white crystals of HgCl2.
See
http://www.sciencemadness.org/talk/viewthread.php?tid=3842&a...
[Edited on 4-12-2008 by Magpie]
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S.C. Wack
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The yellow precipitate of the basic sulfate will go back to the normal sulfate on heating with conc. H2SO4, which will give yellow HgO with NaOH or
KOH instead of the basic salt formed with (bi)carbonate.
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gobbles
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@Magpie: The supernatant was clear and colorless. A small amount was evaporated, leaving what I believe to be sodium sulfate. The residue did not
sublime no matter how much heat I threw at it.
@S.C.Wack: after washing the bright yellow crystals with cold water I converted them back to HgSO4 with 75% H2SO4, so I had the basic sulfate, Hg3O6S.
I then made up a concentrated solution of NaOH and added it to the sulfate/sulfuric acid solution in small amounts with swirling. Of course, it
didn't go as planned. Upon addition, the ugliest yellow/orange sludge formed at the surface, then disappeared. I figured I would convert the HgSO4
to the insoluble HgO leaving the soluble sodium sulfate in solution, then wash the oxide and proceed to the chloride. I've reached the capacity of my
little flask and still don't have any visible HgO, although the volume of the HgSO4 crystals has diminished. Tomorrow I will transfer everything to a
larger flask and maybe continue adding lye solution. The solution got really hot during this reaction, so maybe the oxide will crash out when cool.
It's not supposed to be soluble though.
This is getting to be a freakin' dangerous mess. I'm about to dump the mess into fresh concrete and start over with Mr. Anonymous' prep., which sound
much safer. Plus, my liver hurt for a couple days there, but it's probably in my head, I've got no other symptoms of mercury poisoning. I have been
really careful.
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prole
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Your mercuric oxide is being converted back into mercuric sulfate as soon as it's being formed, due to the presence of sulfuric acid.
[Edited on 12/10/2008 by prole]
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Rosco Bodine
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Hmmm, maybe Mr. A is onto something there 
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starman
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(4) Mercuric Chloride. HgCl2 .
Dissolve about five grams of metallic mercury in aqua regia.
Evaporate to dryness on a water bath. Place the residue into
a small dry flask, cover the latter with a watch-glass, and heat
cautiously on a sand-bath. What is the sublimate formed in
the upper part of the flask ? Dissolve it in four parts of boiling
water and allow to crystallize.
Above is a quote from an old (1911) students preparation manual.Interestingly there seem to be no hazard warnings about preparation of potentially
lethal compounds.
My questions are how hazardous is the sublimation?If one were to conduct this outdoors with due precautions is it any more dangerous than Mr A's 2
step evolutions of NOx?
If the product is to be used for amalgamation purposes is the sublimatiion even required?
All in all this seems much simpler and direct than either Mr A or Zygoat.I'm assuming there must be other issues as to why it fell out of favour?
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chochu3
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In my first post heat would have to be used (chlorine and mercury). Their is a wet method which uses HgO + 2HCl (aq) -> HgCl2 + H2O
To get mercury (II) oxide one would need mercury (II) nitrate and add it to an excess of sodium hydroxide which would yield the oxide as a yellow
precipitate. At first adding sodium hydroxide in small amounts will form a brown red precipiate till a stoichiometric amount is added when it will
form a yellow precipitate.
Strong oxidizing acids would be needed to reduce mercury to either +1 or +2 state. Such as nitric or sulphuric acid. If mercury is in excess it will
be reduced to the +1 state, if the acid in excess it will be reduced to the +2 state.
A qualitive analysis in vogel's book says adding aqueous ammonia to mercury in it +1 state will form a complex and oxidize the mercury to its element
forming a finely divided mercury as a black precipitate. It also reduces some of the mecury to mecury (II) amido anion forming a precipitate also.
[Edited on 14-12-2008 by chochu3]
\"Abiding in the midst of ignorance, thinking themselves wise and learned, fools go aimlessly hither and thither, like blind led by the blind.\" -
Katha Upanishad
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Foss_Jeane
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| Quote: | Originally posted by Zinc
A little OT but can mercury be obtained by electrolysis of the solution of HgCl2? |
Yes, of course it can. Be sure to use a carbon, iron, or platinum cathode otherwise the liberated mercury will amalgamate with the cathode metal.
You'll also need a carbon anode so that you won't be getting contamination from the anode.
Even better, use a partitioned cell for the anode and collect the chlorine in damp CaO to make Ca(OCl)2 and Ca(OCl)Cl as an added bonus, and to keep
chlorine out of the air you're breathing while doing this.
[Edited on 19-12-2008 by Foss_Jeane]
[Edited on 19-12-2008 by Foss_Jeane]
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Microtek
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| Quote: |
Strong oxidizing acids would be needed to reduce mercury to either +1 or +2 state. Such as nitric or sulphuric acid. If mercury is in excess it will
be reduced to the +1 state, if the acid in excess it will be reduced to the +2 state.
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You've got your redox chemistry backwards. Oxidizing acids do not reduce free metals, they oxidize them. Metal atoms going from the 0-state (free
metal) to +1 or +2 are being oxidized, not reduced.
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