Why does my colloidal gold solution turn from ruby red to clear when ascorbic acid is added?

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IsaacUS

Member
Joined
Jul 21, 2019
Messages
23
The colloidal gold was prepared using pure .999 gold and de-ionized water. The solution Is ruby red. When I added ascorbic acid the solution turned clear.
What exactly took place?
 
My wild ass guess would be that you had produced a slurry of gold oxides or chlorides. Ascorbic acid in this system would be a reductant, reducing oxidized gold (or silver) to metal. I know that ascorbic acid is used to produce silver nanoparticles via reduction in slurry, so I would guess that it would also do that with gold.

If the particles are small enough, they don't refract light sufficiently to create colors. So, reducing a complex gold oxide (probably an agglomerated gold-gold oxide clump) to gold metal would significantly reduce the size and therefore eliminate light refraction (e.g. color). For that matter, if the ascorbic acid just got rid of clumps which often form just due to Van der Waals forces, it would also eliminate color.

Again, wild ass guess (WAG).
 
Geraldo said:
My wild ass guess would be that you had produced a slurry of gold oxides or chlorides. Ascorbic acid in this system would be a reductant, reducing oxidized gold (or silver) to metal. I know that ascorbic acid is used to produce silver nanoparticles via reduction in slurry, so I would guess that it would also do that with gold.

If the particles are small enough, they don't refract light sufficiently to create colors. So, reducing a complex gold oxide (probably an agglomerated gold-gold oxide clump) to gold metal would significantly reduce the size and therefore eliminate light refraction (e.g. color). For that matter, if the ascorbic acid just got rid of clumps which often form just due to Van der Waals forces, it would also eliminate color.

Again, wild ass guess (WAG).
Click to expand...
Thank you sir, for that wild ass guess.
You gave me a map as to where I need to look.

Nanoscience is just amazing man. This field goes into chemistry, physics, and medicine. Just learning and doing experiments with it to gain some knowledge.

Why won't the moderators on this site create a nanoscience/material science section
 
Lino1406 said:
Ascorbic acid is acting here as an acid, not reducer. Breaking the colloidal structure
Click to expand...

Interesting.
So does it essentially dissolve the gold nanoparticles in this process?
Any ideas on the equation to this reaction? Just want to know what truly is going on
 
butcher said:
Ascorbic acid is often used as a reducing agent in combination with a stabilizing agent to make colloidal gold solutions.
Click to expand...


It's also a crackingly good way to precipitate gold from an AR solution.
 
philddreamer said:
Thanks Lino!

https://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=12496&p=284004&hilit=colloidal+gold#p257374

Phil
Click to expand...

The second post of that discussion:
First of all try to find the information about how to handle sulphuric acid(it has been posted many times here in the Forum).

After you have read it then add some sulphuric acid to your gold colloidal solution,heat it until boiling and mantain boilng for 1 hour,let settle down for a night and you will see a brown/black mud,which is your gold.

Hope it helps.

Kindest regards.

Manuel


Why would a black/Brown sludge be seen? The amount of gold in colloidal gold is negligible. Unless the sulfuric acid, boiling then settling, messed around with the metallic gold particle size/mass. But that's impossible
 

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