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Mixing aqua regia


#1

The situation: I want to mix Aqua Regia. I have hydrochloric acid,
HCl, at 23% and nitric acid, HNO3, at 53%, ie. both at
hardware-store grades.

My problem: Anybody can explain to me the math to mix my own AR? I
guess there are adjustments to be made for the dillution percentages
of the acids!?

Oppi Untracht say the “usual” AR is
HCl : 3 parts by volume
HNO3 : 3 parts by volume

He further notes that AR for 14 - 18 kt gold is
HNO3 : 49 parts by volume
HCl : 1 part by volume
Distilled water : 12.5 parts by volume

I am looking to understand how to convert these "parts by volume"
recipes into volumetric recipes that take the dilution, or grades,
of the acids into consideration.

Thanks a ton in advance,
Andreas


#2

its important to understand in aqua regia its the HCl which is
reacting with the gold to form Chloroauric acid (sometimes
mistakenly called gold chloride). the nitric acid is behaving almost
like a catalyst. as a result, the exact proportions aren’t necessary
and that’s why there are so many variations. this video explains the
process very well. http://www.youtube.com/watch?v=iwnKU89CCdI

I would stick with 1 part HNO3: 3 parts HCl as both your acid are
about the same dilution. (I know it seems that you’re 23%
hydrochloric acid is dilute but consider that 36+% is considered
concentrated)