thrival
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How to reduce HgCl back to metal?
Is there a simple, fast and/or efficient way to do this? I read the metals all do this but forming amalgams isn't useful to me, I want my liquid
quicksilver back!
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blogfast25
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You mean HgCl<sub>2</sub>, right? Mercuric chloride.
Mercuric ions are easy to reduce:
Hg<sup>2+</sup>(aq) + 2 e- -----> 2 Hg(l) has a reduction potential of +0.85 V
(http://chemprof.tripod.com/redtable.htm)
Anything with a lower reduction potential is thus in principle capable of reducing the mercuric ions to mercury metal. Copper for instance would do
it.
So make solution of mercuric chloride and choose a reducing metal, preferably one that doesn't amalgamate with mercury easily.
Gentle electrolysis of an aqueous mercuric chloride solution with carbon electrodes should also work well.
Mind the high toxicity of all things mercurial!
[Edited on 14-2-2015 by blogfast25]
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Boffis
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Which mercury chloride is it though? Do you have:
Hg2Cl2 - mercurous chloride - the insoluble type
HgCl2 - mercuric chloride - the soluble type
Both chlorides are decomposed by a large excess of alkali hydroxide. When a suspension of mercurous chloride is treated with excess hot alkali
hydroxide it is converted to a black mixture of mercury and mercuric oxide. Without isolation the mercuric oxide can be reduced by almost any reducing
agent but hydrazine or hydroxylamine are usually used because they are clean (oxidation products N2 and H2O).
I suspect therefore that mercuric chloride with be similarly converted to mercuric oxide by excess alkali and can then be reduced to mercury as above.
Mercuric chloride is a curious compound because it is almost undissociated and while the nitrate and sulphate immediate deposit yellow mercuric oxide
the chloride may not. In neutral and acid conditions almost all reducing agents precipitate the mercurous chloride apart from a few sulphur bearing
compounds (ie thiosulphates) when the reaction is complex and the precipitate is discoloured by sulphur containing compounds.
Avoid ammonia because it converts both valencies of Hg into hellish intractable aminomercury compounds. I suggest you read up on some mercury
chemistry though before you try this reduction. There are a couple of comprehensive textbooks on the SM website library.
These things said I think your best route is via reduction in alkali hydroxide to avoid the formation of mercurous compounds.
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SimpleChemist-238
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Here is a good chart!
We are chemists , we bring light to the darkness. Knowledge to ignorant, excitement to the depressed and unknowing. we bring crops to broken fields
and water to the desert. Where there is fear we bring curiosity.
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Cou
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Be VERY careful with mercury compounds. Mercury accumulates in your body, increasing the chance of cancer and brain damage.
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MrHomeScientist
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SimpleChemist, I have that very chart posted on my wall right now! Very handy reference.
Iron flasks are traditionally used for mercury storage and transport, because the metals do not form an amalgam. My dad used to tell stories of how he
would rub mercury onto pennies to give them a silvery shine - from that I conclude that copper would not be the best choice for reduction. If that
isn't strictly amalgamation, it at least sticks to copper and would be difficult to remove. Perhaps an iron bar dropped in a solution of
HgCl<sub>2</sub> (assuming that's what you have) would do the trick. Be sure to come up with a safety & waste disposal plan before
conducting any experiments with soluble mercury compounds!
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