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neutrino
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I tested my solution and it came out negative. I think the flocculent precipitate at the bottom of the solution contains gold, I must check some
solubilities to be sure.
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Ephoton
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Mood: trying to figure out why I need a dark room retreat when I live in a forest of wattle.
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nice one :)
I would disolve some of the precipitate then add tin
if you get a purple precipitate its got gold in it.
purple cassias.
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AndersHoveland
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Aqua Regia
The mix of concentrated nitric and hydrochloric acids in aqua regia exists in an equilibrium. The equilibrium only begins moving to the right when the
acids are very concentrated. Even heating 30% conc HCl with NaNO3 will give off some brown fumes.
HNO3 + (3)HCl <==> (2)H2O + NOCl + Cl2
(2)NOCl + H2O --> NO + NO2 + (2)HCl[aq]
Aqueous solution of chlorine can attack gold.
(2)Au + (3)Cl2 + (2)Cl[-] --> (2)AuCl4[-]
An interesting way to reduce gold(III) chloride back to elemental gold is to use an alkaline solution of hydrogen peroxide. Although usually oxidizer,
in some reactions H2O2 can act as a reducing agent.
(2)AuCl4[-] + (3)H2O2 + (6)OH[-] --> (2)Au + (8)Cl[-] + (6)H2O + (3)O2
The gold usually separates out in a finely divided state, and appears brown by reflected light and greenish blue by transmitted light. If very dilte
solutions are used, the gold sometimes separates out forming a yellowish film on the sides of the test tube.
[Edited on 11-10-2011 by AndersHoveland]
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BJ68
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Old Thread, but I obtained 20 g gold pellets and will sacrifice about 2 g for making Gold(III)chloride.
I found this article: "A Straightforward Route to Tetrachloroauric Acid from Gold Metal and Molecular Chlorine for Nanoparticle Synthesis" http://www.mdpi.com/2075-4701/5/3/1454/pdf and will use this method.
The only things what I will change is
a) the solution will be evaporated in a rotary evaporator under vacuum and not freeze dried to obtain Gold(III)chloride.
b) the volume of HCl (down to under 50 ml)
c) mass of gold (1-2g)
Problems what I see:
Changing the concentration of the produced Tetrachloroauric Acid can influence the stability of the solution....and the heating will be critical, too.
Very clean flasks have to be used....
Opinions?
Bj68
[Edited on 1-2-2017 by BJ68]
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nezza
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The beauty of using Aqua Regia is that all of the products are volative or gases so the gold solution can be evaporated to leave pure aurichloric
acid. Any other route leaves solid impurities which are difficult to remove without reducing the gold(III) back to metallic gold. Adding alkali to
aurichloric acid does not generally precipitate any gold oxides but does make the solution incredibly sensitive to reduction to metallic gold. I
appreciate that in some countries in the EUSSR it is impossible to buy nitric acid of any useable concentration now, but small amounts can be
distilled from nitrates and phosphoric acid.
If you're not part of the solution, you're part of the precipitate.
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BJ68
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Hm....sorry but if you look at the paper: They use only hydrochloric acid and pure chlorine and nothing else. Hydrochloric acid is the main ingredient
of Aqua Regia and chlorine is volatile.
So which advantage do I have if I use Aqua Regia? They only thing I think is the time advantage....with Aqua Regia it goes much faster, but so far
what I have read you have to make sure, that all nitric acid is evaporated...that means you have to add hydrochloric acid and boil down the liquid a
few times until no brownish vapors are visible.
Bj68
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Sulaiman
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I would go for the Aqua Regia (AR) route, (I found it surprising how fast gold 'dissolves')
add excess HCl to Au, heat, add HNO3 until just a little gold is left,
this ensures that there is no excess nitric acid to be removed 
the HCl boils off easily, leaving HAuCl4 as pure as your starting components.
a simple one pot synthesis.
recover any precipitates (e.g. un-reacted, or precipitated gold) by decantation as filtering always results in mechanical losses.
EDIT: afterthought .. I have not recovered HAuCl4 crystals this way, I jist meant that MOST of the HCl boills off easily, I did not try
further.
but, when I tried direct 2Au + Cl2 = AuCl I got more AuCl3 than AuCl
[Edited on 1-2-2017 by Sulaiman]
[Edited on 1-2-2017 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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BJ68
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Can check both routes....working at a University, so supply with reagents is not a problem...and if some thing goes wrong, I can recycle the "waste".
Bj68
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j_sum1
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Dang it is frustrating how many experiment ideas that I have been mulling over for a while have resurfaced on the board when I am still sans lab.
Sulaiman presented some interesting stuff last year on the twelve keys of Basil Valentine and the making of AuCl3 appears to be key 3. This graphic
shows his procedure. (The illustration was done by someone other than Valentine.)
Attachment: 03.Musaeum_Hermeticum_1678_p_398_III._Clavis_AQ27.tif (4.6MB)
This file has been downloaded 715 times
It is worth looking up Valentine's description of the procedure and also the modern interpretation of it. I can't lay my hands on it just at the
moment. But the key to his process is the fighting roosters and fox in the midground. The fox is aqua regia (the only sneaky thing that can dissolve
gold.) The rooster is the gold. The fox consumes the rooster. The rooster consumes the fox. Through evaporation the rooster is regenerated. A
cycle of repetitions eventually gives a chlorinated atmosphere. And when it becomes anhydrous the fiery red crystals of dragon's blood appear.
AFAIK, auric chloride is very sensitive to water - deliquescent and so difficult to make and store. Also excessive heating drives off Cl2 leaving
gold again.
I have devised a procedure that I intend to try later this year. Anhydrous conditions and reacting the gold directly with Cl2 and NO2. No idea how
successful I will be but that is half the fun.
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