Author Topic: pH of AuCl3  (Read 3597 times)

Glen

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pH of AuCl3
« on: November 25, 2013, 04:35:56 AM »
Hi,
Can anyone tell me what the pH of their AuCl3 solution is? I am making some from Au metal and need to know what to adjust the pH to keep the colloidal gold recipe the same (or adjust, I haven't decided which way to go yet).

Thanks in advance.

Offline mraluma415

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Re: pH of AuCl3
« Reply #1 on: November 25, 2013, 04:44:23 AM »
If distilled water sits around 6.5-7.0, I would assume gold chloride is around 4.5-5.0

It is difficult to measure its pH without a special meter, but it is slightly more acidic than pure water.
"The art of healing comes from nature, not from the physician. Therefore the physician must start from nature, with an open mind." - Paracelsus

Glen

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Re: pH of AuCl3
« Reply #2 on: November 25, 2013, 04:55:51 AM »
Thanks,
I use these test strips most of the time, mostly just the ones that read to 1 (because they're cheaper).;
https://www.labfriend.com.au/c/651/0/ph-indicator-strips-non-bleeding-pack-of-100-strips
They are accurate enough for most things and compare well to the bench meter.

Cheers

Offline mraluma415

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Re: pH of AuCl3
« Reply #3 on: November 25, 2013, 07:11:58 AM »
I had forgotten I have some test strips lying around. It looks as though the color is registering around 2.5-3.0 with an umber/red.

"The art of healing comes from nature, not from the physician. Therefore the physician must start from nature, with an open mind." - Paracelsus

Offline kephra

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Re: pH of AuCl3
« Reply #4 on: November 25, 2013, 04:24:22 PM »
Remember that the solution is actually HAuCl4.  For the 1% solution that Salt Lake Metals sells, the pH should theoretically be 1.3.
Their solution is 1% gold by weight, which makes it .05 Molar.
Since there is a one to one relationship between gold and hydrogen in the HAuCl4 molecule, the H+ is also 0.05 Molar
pH is the negative logarithm of the hydrogen ion concentration, so log10 of 0.05 equal -1.3 making the ph 1.3

When diluted to make colloidal gold using 4 ml of the gold chloride solution per liter (40 ppm) the pH should then be 3.7
Each ml of the gold chloride contains 10 mg of gold, so 4 ml is 40 milligrams
40 milligrams of gold is .0002 moles of gold and .0002 moles of Hydrogen ions.
Then log10 of 0.0002 = -3.69 for a pH of 3.69.

Of course it wont be exact because the starting pH of the water will not be exactly 7, and there may be some residual hydrochloric acid in the gold chloride solution.  But this should give you a really good guess.

 
There is the unknown and the unknowable.  It's a wise man who knows the difference.

Offline mraluma415

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Re: pH of AuCl3
« Reply #5 on: November 25, 2013, 06:01:42 PM »
That is a great response Kephra!  I always wanted to know this value as well. I will take note of this equation.
"The art of healing comes from nature, not from the physician. Therefore the physician must start from nature, with an open mind." - Paracelsus

Glen

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Re: pH of AuCl3
« Reply #6 on: November 26, 2013, 02:29:03 AM »
Thanks Kephra, you answered all my questions. I'm in Aus and I had a look around at what I could buy pre-made for the gold chloride and most of it was in some concentration of HCl so I wanted check what your instructions were based on. Maybe I should have asked that question. All of the pre-made options were pretty expensive (unless there's someone else from Aus on here who knows somewhere) hence making it myself.