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Aqua Regia, how strong is it?
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nebx123
science forum beginner


Joined: 13 Jul 2006
Posts: 1

PostPosted: Thu Jul 13, 2006 3:40 am    Post subject: Aqua Regia, how strong is it? Reply with quote

Aqua Regia is supposedly mixture of hydrochloric acid and nitric acid,
strong enough to melt gold and other materials not usually effected by
acid. I want to know how strong it is compared to say, H2ClO4 and other
strong acids. I would also like to know how to contain such a
substance.
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Bob111
science forum Guru Wannabe


Joined: 13 Jan 2006
Posts: 115

PostPosted: Thu Jul 13, 2006 6:16 am    Post subject: Re: Aqua Regia, how strong is it? Reply with quote

On 12 Jul 2006 20:40:17 -0700, "nebx123" <nebx123@gmail.com> wrote:

Quote:
Aqua Regia is supposedly mixture of hydrochloric acid and nitric acid,
strong enough to melt gold and other materials not usually effected by
acid. I want to know how strong it is compared to say, H2ClO4 and other
strong acids. I would also like to know how to contain such a
substance.

Let's clarify some things...

No such thing as H2ClO4. I presume you mean HClO4 = perchloric acid.

Aqua regia does not "melt" gold. It "dissolves" it -- a totally
different phenomenon, and even saying that is a simplification.

Now, the really bad one. Strong. It means different things. There is a
concept of acid strength (and also concentration, sometimes sloppily
called strength). But acid strength, in strict sense, has little to do
with why aqua regia works. Yes, the acid part is good, but aqua regia
works because both the Cl- and NO3(-) are active players in the
overall process of dissolving gold. Briefly, the nitrate is a good
oxidizing agent, and the chloride is a good complexing agent for gold.
So, together acid + oxidizing agent + complexing agent and one can get
the gold to react and form a soluble complex.

bob
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Repeating Rifle
science forum Guru Wannabe


Joined: 25 Mar 2005
Posts: 205

PostPosted: Thu Jul 13, 2006 4:58 pm    Post subject: Re: Aqua Regia, how strong is it? Reply with quote

On 7/12/06 11:16 PM, in article 8sobb2dqruv03ti8dnd9ibcnbi0l358rej@4ax.com,
"Bob" <bbx107.XYZ@excite.XYZ.com> wrote:

Quote:
Let's clarify some things...

No such thing as H2ClO4. I presume you mean HClO4 = perchloric acid.

Aqua regia does not "melt" gold. It "dissolves" it -- a totally
different phenomenon, and even saying that is a simplification.

Now, the really bad one. Strong. It means different things. There is a
concept of acid strength (and also concentration, sometimes sloppily
called strength). But acid strength, in strict sense, has little to do
with why aqua regia works. Yes, the acid part is good, but aqua regia
works because both the Cl- and NO3(-) are active players in the
overall process of dissolving gold. Briefly, the nitrate is a good
oxidizing agent, and the chloride is a good complexing agent for gold.
So, together acid + oxidizing agent + complexing agent and one can get
the gold to react and form a soluble complex.

I have A followup question. Does aqua regia have to be freshly mixed in
order to be effective?

Bill
-- Ferme le Bush
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rekuci@gmail.com
science forum addict


Joined: 22 Sep 2005
Posts: 98

PostPosted: Thu Jul 13, 2006 7:07 pm    Post subject: Re: Aqua Regia, how strong is it? Reply with quote

Quote:
I have A followup question. Does aqua regia have to be freshly mixed in
order to be effective?

I don't see why it would need to be fresh, so long as the solution is
contained and you don't lose HCl over time as a gas.
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Ron Jones
science forum Guru Wannabe


Joined: 16 May 2005
Posts: 175

PostPosted: Thu Jul 13, 2006 7:10 pm    Post subject: Re: Aqua Regia, how strong is it? Reply with quote

Salmon Egg wrote:
Quote:
On 7/12/06 11:16 PM, in article
8sobb2dqruv03ti8dnd9ibcnbi0l358rej@4ax.com, "Bob"
bbx107.XYZ@excite.XYZ.com> wrote:

Let's clarify some things...

No such thing as H2ClO4. I presume you mean HClO4 = perchloric acid.

Aqua regia does not "melt" gold. It "dissolves" it -- a totally
different phenomenon, and even saying that is a simplification.

Now, the really bad one. Strong. It means different things. There is
a concept of acid strength (and also concentration, sometimes
sloppily called strength). But acid strength, in strict sense, has
little to do with why aqua regia works. Yes, the acid part is good,
but aqua regia works because both the Cl- and NO3(-) are active
players in the overall process of dissolving gold. Briefly, the
nitrate is a good oxidizing agent, and the chloride is a good
complexing agent for gold. So, together acid + oxidizing agent +
complexing agent and one can get the gold to react and form a
soluble complex.

I have A followup question. Does aqua regia have to be freshly mixed
in order to be effective?

Depends how old. It will slowly give off NOx, while there is still some NOx
and Cl then it will dissolve gold - not that quick when cold, really needs
heating to get a reasonable rate of gold dissolution. The product, of
course, is chloroauric acid, if you boil off all the acid, that's what you
get left with.

--
Ron Jones
Process Safety & Development Specialist
Don't repeat history, unreported chemical lab/plant near missesa at
http://www.crhf.org.uk Only two things are certain: The universe and
human stupidity; and I'm not certain about the universe. ~ Albert
Einstein
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