Talk:Aqua regia/Archive 1

Gold Metal or Ion?
The following phrase is a ambiguous: "which react with the gold to produce chloraurate anions." Is the article referring to the gold metal or the Au3+ ions produced by reacting with nitric acid? absolutecaliber

The sentence is accompanied by the relevant equations. The equation shows that the chloride ions react with the ionized gold (Au3+). The sentence is unambiguous if viewed in this overall context. Leeannedy 20:18, 1 November 2006 (UTC)

-- If painters did use aqua regia to clean their brushes, the metal parts would dissolve and the organic parts would be burned. I think, if they did once use something called aqua regia, it must have been something different. Can you verify your info source? -- Marj Tiefert 09:13 Jul 21, 2002 (PDT)
 * Of course, they use it in a light solution (with water, I'd think) that allows to do it without damages. I believe that the substance keeps this name even if it is in a poor concentration. As for what I personally directly know, a close friend of mine was a reputed painter and I still remember the typical smell of aqua regia in his "studio", as well as the regular, unavoidable operation of cleaning the brushes in it at the end of the work. We call it "acquaragia", but my dictionary confirms me we should be talking about the same substance; if anyone here can tell the correct name of what painters do use for this purpose, I might check if we have a different translation and, consequently, if I just made a silly mistake (hope not! :-))). -- Gianfranco

Aqua Ragia is more commonly known as turpentine in English and is a completely different substance from Aqua Regia -- Derek Ross
 * Well, I made a silly mistake, we use the same "acquaragia" for both and I got lost in the middle. Sorry for the confusion... -- Gianfranco
 * Put that in the article! - Omegatron 22:41, Feb 4, 2005 (UTC)

According to, it would seem that the Nobel prize medals which were dissolved into aqua regia were, in fact, created from "fresh" gold rather than that dissolved into the solution.- Caspian 11:26, Oct 31, 2005 (EST)
 * It's not clear, but at the end of the article it says that Francke was given a "recoined" medal, which suggests that at least his was made from the same gold. KarlM 04:40, 25 July 2006 (UTC)

Copper doesn't dissolve?
I put a penny into some fresh aqua regia (Yellow and fuming). Nothing happened. Why doesn't the copper get oxidized as it does in HNO3? —The preceding unsigned comment was added by 71.142.218.139 (talk • contribs).


 * While I highly doubt that you actually used aqua regia (if you have access to these sorts of chemicals, one would think you would know the answer), I'll try to humor you. First of all, the penny is not pure copper: it's an alloy of metals plated in copper. It's 97.5% zinc (courtesy of our very own Cent (United States coin) article). However, aqua regia should still be strong enough to dissolve zinc too. Check the dilutions: the acids you used probably weren't high enough concentration. However... IANAC (I am not a Chemist) &mdash; Ambush Commander (Talk) 03:06, 26 February 2006 (UTC)

It's not that hard to find sulfuric and nitric acid. I purchased both off eBay and produced my own aqua regia. absolutecaliber


 * They both have to be at dangerous concentrations though. &mdash; Edward Z. Yang (Talk) 02:20, 15 November 2006 (UTC)

absolutecaliber, Sulfuric Acid is not a component of aqua regia.

Maybe the penny was greasy?

A thin, invisible coating of mineral oils would have protected it for a while against nitric acid or mixtures containing it.

Concentrated nitric acid turns yellow with age, and fumes.

Aqua regia - concentrated hydrochloric and nitric acids - would certainly have attacked bare copper or a copper-zinc alloy. Nitric acid alone attacks copper, but hydrochloric and sulfuric acids alone do not. A mixture of nitric and sulfuric acid should have had some effect on bare copper. Copper is less easily oxidized than hydrogen (acid, H+), but can be oxidized by nitrate/nitric acid. Zinc is very easily oxidized by hydrogen, but whether the penny alloy could be dissolved or damaged by acid as a result depends on whether the zinc is exposed on the surface and whether it is present as a pure metal in solid state solution or (more likely) as an intermetallic compound.

There may be a thin layer of pure copper on the surface of a penny, which would prevent it from reacting with hydrochloric or sulfuric acids alone or in combination with one another.

Bg8520 (talk) 16:34, 16 July 2009 (UTC)

Form of Gold in Solution
Each of the referenced external links indicates that the dissolved form of the gold is the anion chloraurate (AuCl4-) rather than the acid form chlorauric acid (HAuCl4). In which form is the dissolved species of the gold? I assume that in reality an equilibrium is present between the chloraurate and chlorauric acid. In this manner, the dominant species would depend on the acid dissociation constant of chlorauric acid and the concentration of hydronium ions. Since the oxidation reaction generates water, the hydronium concentration will vary with the quantity of gold dissolved. Can someone shed some light on the typical dominant form? If the dominant form is the chloraurate anion, I believe the reactions should be changed to reflect this (since they are written in ionic form). Leeannedy 12:25, 11 March 2006 (UTC)

Color of aqua regia
I was once a chemical techician in a semiconductor plant, and I used to wash quartz-glass ampules in aqua regia before they were used in a diffusion oven. I don't know why Columbia Encyclopedia would say it is yellow. It is only yellow for a little while. When you first mix the HCl and the HNO3 it is clear. Within a minute or so it starts turning yellow, but goes from there to orange and finally a deep red, like boiling, fuming cherry Kool-Aid. It is an amazing thing to behold. Scary, but you learn to be very careful when you're up to your elbows in that stuff under a fume hood. If you're going to pick one color for it, you'd definitely pick red if you ever worked with it. 128.244.230.13 21:26, 19 April 2006 (UTC)Richard Waddel

1Aug06RLC I made up a solution for semiconductor use and the color is pink or red with bubbles. Semiconductor solution is different than standard Aqua Regia mixture. The mixture difference may cause different solution color. Semiconductor Mix HNO3:HCl  (2:1) , Standard Mix  HNO3:HCL  (1:4)


 * I've reverted it, because most other sources on the web say it's yellow. I understand that your personal experience may tell you otherwise, so if you can find a reputable source, we should make note of the color changes in the article. &mdash; Edward Z. Yang (Talk) 00:36, 20 April 2006 (UTC)


 * Ah, this source says it's red, yellow or gold. Will reword accordingly. (you're right). &mdash; Edward Z. Yang (Talk) 00:38, 20 April 2006 (UTC)
 * I've worked with it a lot- the colour will change depending on how exactly you've measured the hydrochloric and nitric acids. If you've got more nitric than the recipe calls for, the acid will be more reddish.  Of course, if it sits for too long and the NO2 is allowed to evaporate, the colour fades to yellow.Tressure 21:40, 7 June 2007 (UTC)


 * If there are metals or organics available to be oxidized, the bright reddish color never fully develops, and the color is deeper with heat, though it is also more transient. The article mentions cleaning NMR tubes with aqua regia to remove organics, but I find that Caro's acid (sulfuric acid plus persulfate ion or hydrogen peroxide) is far more effective than aqua regia for removing traces of organic material. Norm Reitzel (talk) 18:18, 25 September 2009 (UTC)

For metal etching such as in swords, the solution should be aged for a month, I don't know why. This may account for different color observations.


 * Also, for use with iron or steel, the solution is often saturated with iron ions by dissolving scrap. The resulting etch is pale yellow. Norm Reitzel (talk) 18:18, 25 September 2009 (UTC)

disactivation of Acqya regia
Hi every body, I need to know if it is possibile, and if yes, how to disactive Acqua regia in yor lab? If any one knows, please send me your information best regards Nabil
 * The same way you neutralize any other acid. (seriously though, I am not a chemist and if you have Aqua Regia but don't know how to disable it, you probably shouldn't be either.) Please direct non-article related questions to the help desk. &mdash; Edward Z. Yang (Talk) 19:06, 21 August 2006 (UTC)

Do you mean neutralise? A lot of sodium bicarbonate (baking soda) is always a good way to neutralize an acid. 24.210.248.224 17:32, 17 September 2007 (UTC) Sorry Though I was logged in. Jasoninkid 17:34, 17 September 2007 (UTC)

precipitated the gold out of the acid?
How would this be possible? —The preceding unsigned comment was added by Archangel991 (talk • contribs).


 * Since gold is such an unreactive metal, dissolving it is the hard part. Getting it back into metal form is easy. Just add any weak reducing agent. This website says: "The gold can then be selectively precipitated using a number of reducing agents, such as ferrous sulphate (also known as Copperas), sodium bisulphite, and sulphur dioxide gas. Other less frequently used agents include hydrazine, formaldehyde, oxalic acid, and hydroquinone." —Keenan Pepper 00:03, 2 September 2006 (UTC)

History
How dos NaCl + H2SO4 --> HNO3 + HCl? Where dos the N come form and what happens to the S? I think he had at his hands both HNO3 and HCl by 800. Jasoninkid 17:38, 17 September 2007 (UTC)

Or maybe I should learn to read, never mindJasoninkid 17:46, 17 September 2007 (UTC)

Conflict of Facts
According to the Irridium page, Irridium "Cannot be attacked by aqua regia" however,assuming that "attacked" means dissolved, then there is a problem; according to the aqua regia page, the mixture is named thusly because it can dissolve noble metals including Irridum. I don't know which statement is true, so I will change neither, but I put this information on the Irridium talk page as well.

Digressionfromatanget (talk) 23:13, 26 February 2008 (UTC)Digressionfromatangent


 * I don't see any contradiction; this article explicitly gives iridium as an exception: "it can dissolve the so-called royal, or noble metals, although tantalum, iridium, and a few other metals are able to withstand it." --Itub (talk) 07:38, 27 February 2008 (UTC)

Mention of the EPA in an international article
This is an international article, so the reference to the EPA might not be the most appropriate, given it is most commonly known as an agency in the United States. There are a few other EPAs but this is not the best measure or reference for this purely scientific articles. Any suggestions for a more neutral or general reference? "This practice should not be used when EPA regulated or otherwise toxic metals are present." —Preceding unsigned comment added by 78.16.202.194 (talk) 09:33, 30 August 2008 (UTC) I noticed the mention of the non-international EPA also. How about: "This practice should not be used when environmentally regulated or otherwise toxic metals are present."Wileedingo (talk) 23:41, 3 December 2008 (UTC)

Other acids that dissilve noble metals
Are there any other acids that will dissolve metals like gold and platium —Preceding unsigned comment added by 81.79.21.27 (talk) 13:02, 8 December 2008 (UTC)

Importance of elemental chlorine in the dissolution of gold
I have not been to the literature yet to clarify this point for myself.

My understanding of aqua regia has been that in a concentrated solution of nitric and hydrochloric acids, a oxidation-reduction equilibrium is established between nitric acid/nitrate and chloride on one side and nitric oxide/nitrous acid/nitrite and elemental chlorine on the other. It is the nitric oxide is responsible for the fumes and the red color of aqua regia. I understood that it was the elemental chlorine that was the active principle in dissolving bulk metallic gold. I had thought that the gold oxide layer at the surface was an effective barrier to further attack by nitric acid/nitrate, but that chlorine was able to penetrate this layer and bring additional gold into solution. I think that if it was just a question of gold cations staying in solution, the oxidation and dissolution of gold by nitric acid alone could still proceed, but would be accompanied by precipitation of gold salts elsewhere. This view conflicts with the description above.

In the meantime, I was curious whether anyone had any comments?

Bg8520 (talk) 15:59, 16 July 2009 (UTC)

Gold does not form oxides naturally (combination of gold with ambient oxygen) and therefore forms no protective oxide layers as other metals do. The lack of reactivity with other compounds is one of the reasons gold is highly prized, and considered a "noble" metal. 66.239.10.153 (talk) 21:05, 23 June 2010 (UTC)Taros

Other varieties of aqua regia
If we replaced HCl by HBr or HF, what will be the properties of that mixture? I think atleast HNO3-HBr mixture will also be similar to aqua regia; even though HBr is a stronger reducing agent.--Anoop.m (talk) 09:23, 5 October 2010 (UTC)

See tetrabromoauric acid. --Rifleman 82 (talk) 16:50, 5 October 2010 (UTC)

Dissolving Gold Mistake
The sentence "Nitric acid is a powerful oxidizer, which will actually dissolve a virtually undetectable amount of gold, forming gold ions (Au3+)" is not accurate. Look at the standard reduction potentials for nitric acid and gold.
 * Au3+ + 3e- → Au - - - - - - - - - - - - - - E = 1.5 V
 * NO3- + 4H+ + 3e- → NO + 2H2O - - - E = 0.96 V

Nitric acid CANNOT oxidize gold by itself. The function of the chlorides is not simply to make the gold soluble. I would really appreciate it if someone who actually knows something about the mechanism of aqua regia oxidation of gold would share their knowledge with us. I have heard that a chlorine intermediate in reaction of nitric acid and HCl plays a key role, but that is just hearsay. Without any serious mechanistic studies, we are just guessing. My guess would be some sort of associative mechanism of chloride or HCl on the gold surface followed by oxidation with nitric acid. At the very least, our guessing should not violate the most basic rules of redox chemistry. Along these lines, I think that the platinum mechanism is also flawed. El Zarco 06:46, 9 October 2011 (UTC)

also named
regal water — Preceding unsigned comment added by 188.23.92.243 (talk) 16:05, 1 January 2013 (UTC)

mass ratio
the first footnote seems wrong to me!

the "actual" (actual what?) mass ratio of the concentrate acid mixture is not less 2:1

you have:

35% HCl 1,18g/ml 11Mol/l

65% HNO3 1,4g/ml 14Mol/l

you need:

3Mol = 270ml ~ 318g

1Mol = 70ml ~ 98g

that a bit more than 3:1

or - if it means that a 3:1 volume based mixture is it:

300ml HCl = 354mg

100ml HNO3 = 140mg

I don't see the (less than) 1:2 ratio on what is this calulated?

in the case I am wrong - it should be said in a way that other could understand what you mean. --Struppi (talk) 06:30, 3 November 2015 (UTC)


 * See, for example, http://ehs.yale.edu/sites/default/files/Chemical_SOP_AquaRegia.pdf and http://chemistry.about.com/od/acids/fl/How-To-Make-Aqua-Regia-Acid-Solution.htm
 * The 1:3 molar ratio is derived from the following equation:
 * HNO3 + 3HCl -> 2[Cl] + NOCl + 2H2O
 * Most sources specify 1:3 volume mixtures of the concentrated acids. However, the molarities of the two concentrated acids are not the same. HCl is 12.1M while HNO3 is 15.9M. Consequently, a 2:3 ratio of nitric:hydrochloric acids would be closer to the ideal ratio, giving a slight excess of HCl. Figures obtained from http://www.sigmaaldrich.com/chemistry/stockroom-reagents/learning-center/technical-library/reagent-concentrations.html
 * Hope this helps. Plant surfer  12:13, 3 November 2015 (UTC)

History
The first sentence of this section, concerning Jabir ibn Hayyan, conflicts with information in the Wikipedia article on Jabir. The most recent studies in the history of medieval chemistry reveal, in fact, that nitric acid and the other mineral acids were first prepared about the year 1300, centuries after Jabir, and were completely unknown before that time. Older literature (such as that cited here from the writings of Kraus and Holmyard, written nearly a hundred years ago) has been superseded by modern studies. The recent book by the leading scholar of the history of alchemy and early chemistry, Lawrence Principe (cited in the second sentence of the section), establishes that nitric acid was discovered only ca. 1300, not earlier. I propose to change these sentence to reflect this recent scholarship.Ajrocke (talk) 14:04, 25 September 2018 (UTC)

Lots of words and equations, few references
The article is very teachy, but more problematic is that it purports to explain how aqua reqia works and provides many equations with no refs. Looking through Inorganic Syntheses, which makes good use of aqua regia, the equations are simpler:
 * Au + HNO3 + 4HCl→  HAuCl4  + 2H2O + NO
 * Pt + 4HNO3 + 6HCl →  H2PtCl6  + 4NO2 + 4H2O

But given the effort devoted to the current article, I am hesitant to just wipe it out with my sources. --Smokefoot (talk) 14:06, 31 March 2021 (UTC)

Wiki Education assignment: CHEM 300
— Assignment last updated by Re332168 (talk) 04:56, 15 January 2023 (UTC)