Acidity level in Aqua Regia

[mohamedmsud]

I hesitated a lot before asking this question because of my lack of information but anyway .. Is the acidity "ph" related to the effectiveness of Aqua Rigga solution? Is there a certain degree of ph where the solution works better ?

A friend told me that the process should be in a 2.7 ph to be done correctly.
I learned that one of them uses caustic soda husks to adjust the pH as it is less than 2 degrees.
Is this true or is it just a trance.

 

[anachronism]

Hi there

pH is more important in with relation to Aqua Regia when you are precipitating gold using certain precipitants. For the dissolving part is you're using concentrated acids is shouldn't even be an issue.

BTW it's Aqua REGIA- I mentioned this in another thread and the importance of taking care to get the nomenclature correct. 8) Do you think you could ask a Mod to alter the thread title?

It's also pH not ph. 8)

Jon

 

[mohamedmsud]

Thank you for your response , as I said I do not know many things about this topic , I do not speak English fluently, be calm more than that to make new relations , thanks again

 

[ChemGeek]

I hesitated a lot before asking this question because of my lack of information but anyway .. Is the acidity "ph" related to the effectiveness of Aqua Rigga solution? Is there a certain degree of ph where the solution works better ?

A friend told me that the process should be in a 2.7 ph to be done correctly.
I learned that one of them uses caustic soda husks to adjust the pH as it is less than 2 degrees.
Is this true or is it just a trance.

I am afraid, your friend is talking nonsense.
pH of aqua regia is between 0 and 1.
pH of aqua regia is irrelevant in terms of its ability to dissolve gold or other metals.
There are acids much stronger than aqua regia and they still don't dissolve gold.
Examples are conc. sulfuric acid, fluorosulfonic acid or fluoroantimonic acid H2F+SbF6- the strongest acid known to man, which would have pH based on *activity* of H+ in range of -20, means minus 20. These acids still do not dissove gold.
Mind you, this pH of -20 does not make physical sense from perspective of concentration of H+. Said acid is still 20 billions of billions times stronger than concentrated sulfuric acid. For superacids like this one other more suitable scales are designed. Read about Hammett acidity function if interested. This acid can be safely stored in gold, PTFE, or (in absence of oxygen) even in copper containers.
It is aqua regia's oxidating power and ability of chloride anion to complex and stabilize ionic forms of gold what helps to dissove it.
However adjusting pH of AR to 2.7 by caustic soda will make it not working. This is not due to pH increase only due to disapperance of reactive chlorine species present in AR at lower pH and responsible for dissolving gold.

Aqua regia of pH adjusted to 2.7 with caustic soda is essentially a dissolved mixiture of kitchen salt and sodium nitrate and would be suitable for meat pickling but not for gold dissolving. You could even drink a small sample of such "aqua regia" without any acid burns to your stomach, albeit still with care because nitrates are harmful. There are legal limits on nitrates and nitrites content in preserved (pickled) meat.

If you want to dissolve gold around pH 2-3 just use water solution of 1:2 by molar proportion of potassium bromide and bromine. It does dissolve gold nicely at 40-50*C (and at lower temperatures too, but works slower).

 

[mohamedmsud]

I do not know how to thank you .It's valuable information..your answer was enough and clear ,
I will think in another way to pick the meat, it is a new idea for the Egyptians