# Colloidial Gold Questions



## OceanChemist (Jan 30, 2015)

I've recently been diving head first into the scrapping hobby, had some decent experiments on my part, but one is still a mystery, and I'm curious what kind of information if any I can gather from this community.

Here recently while trying to clean up some scrap which mainly consisted of copper filling, using only conc. nitric acid, I found a very purple milky separation of the blue copper nitrate and these purple/red particles that were settling out, and after a few days of searching I have almost convinced myself that this must be colloidal gold, but possibly not, it doesn't dissolve in nitric acid or water, have yet to try org. solvents or HCl, so my question is what could it be if not colloidal gold?
I centrifuged it down, washed it with DI, and for S's and G's It's in my furnace now in a crucible, no fumes, just steadily rising.

Any thoughts? :mrgreen:


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## Palladium (Jan 30, 2015)

Gold in a finely divided state can be purple even black. Especially karated gold plating like gold filled! Plating from electronics which is using pure gold to plate doesn't do it.


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## goldsilverpro (Jan 30, 2015)

By definition, a colloid essentially won't settle. I once read that they found a colloidal gold suspension in an Egyptian tomb that had never settled.


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## butcher (Jan 30, 2015)

Colloidal gold is so small you can only see the reflection of light from the gold in solution, As GSP noted it will not settle.

Stannous chloride (tin chloride salts) can make a gold solution violet.

Silver chloride in light can also give a violet type color.


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## goldsilverpro (Jan 30, 2015)

I've always thought of a colloid being some thing that's not really a solid and not really a liquid, but somewhere in between. Not either but close to both. Like another state of matter. Both smoke and gelatin are colloids.


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## butcher (Jan 31, 2015)

A precipitant can form in less than 0.1 second.

A precipitate we can see, can be crystals (a salt of the metal and acid or base), that form from ions, Cations and Anions which grow to a growth of an ionic crystal large enough for us to see, the ions are so small we cannot begin to see them until they form large clusters of these ionic bonds to form a crystal of ions large enough for us to see, with many bonds of metal Cations and nonmetal Anions bound together to form a large enough crystal to become visible, and a heavy enough practical to sink with gravity.

With gold ions reduced to atoms (say from stannous chloride) the gold atoms are reduced from ions in solution to elemental gold atoms, individual atoms are to small for us to see, even clusters of thousands of these atoms can also be to small for us to see with the naked eye (we may be able to see them with some special microscope),.

It requires something like a cluster of 1000 atoms for the aggregate to be a colloidal particle, with a proximate diameter of 10-7cm . 
Even with a diameter of 10-4cm, containing about a billion atoms the practical is still classified as colloidal and cannot be seen by our naked eye, without a microscope, although we can use a simple method to inspect the solution to see if it holds a colloid in suspension. By a beam of light from a light source like a flashlight, in a darkened room, the light beam viewed from the side as it passes through the solution in our beaker the colloids reflect the light to form a "glow". with gold different size of colloids can reflect different colors of light, color of the solution will appear different for different sizes of colloids (or the size of the clumps of invisible gold atoms) with stannous chloride the atoms clump together to the size that reflects a frequency of light we see as purple. it is not the atoms we see but a purple color of reflected light from the cluster of gold atoms.

Atoms or ions are too small for us to see, but if they join together into a large enough cluster we can see them, colloids are similar but they "develop a charge" before the ions or atoms clusters can grow into large enough of a cluster to become visible to us, stunted in their growth at a size too small to overcome gravity and settle in solution, these small clusters with the same charge repel each other keeping themselves in constant motion in solution shoving each other around, (like small magnets all with the same polarity), unable to come into contact with each other to grow to a larger crystal or clump of atoms, being repelled from each other, they cannot crash into each other to combine into a larger mass to become visible, or to gain in mass to become heavy enough to sink like a precipitant.

A precipitant is a mass of ions or atoms with grow to a large enough size to become visible and to sink.
The precipitant starts off as a colloidal size particles, these small particles crash into each other and combine to a larger crystal or clump of atoms, but does not form a colloid in solution and grows till it forms a visible precipitant or crystal or clumps of atoms we can see, becoming heavy enough to sink in solution. This happens almost instantly when two solution that form the precipitant are added together.

In colloids the ions crystal growth, or the cluster of atoms growth, is stunted before they become large enough to be visible, or heavy enough to overcome gravity in solution, the small clusters forming a polarizing charge as they grow to a certain size, and their growth is halted by the "charge", with a size too small for us to see, they begin to repel each other and will not grow to become visible, will not come together to form a larger particle, or become heavy enough to sink, pushing each around in solution almost indefinably, until something changes to break the colloid, or to remove the electrical charge that keeps them separated and from combining and growing into a precipitant, or dissolves them back into solution as ions.


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## Palladium (Jan 31, 2015)

Very good post Buther! Someone has been doing their research. I've been studying nano silver and learning about capping agents to limit crystal growth. It takes a 1,000 nano meters to = 1 micron and most collides are in the 20-50 nano meter sizes.


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## saadat68 (Jan 27, 2019)

Hi
I Know we can not test solutions that contain gold colloids with stannous chloride. But I have a question.

- If test colloidal solution with stannous chloride, it always shows purple color because we have gold colloids in solution. Right?


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## saadat68 (Jan 28, 2019)

What happen when we test a solution with gold coloides?
Does it shows purple? Even if solution don't contain dissolved gold?


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## butcher (Jan 28, 2019)

A solution of colloidal gold is not always purple, the color comes from the size of the clusters of gold atoms which are locked into solution by electrostatic forces keeping the small clusters of gold atoms in motion in the solution.

When we test a gold solution with stannous chloride the reaction turns purple because of the size of gold colloids which form from the reactions of reducing the gold to metal and the gold atoms join in clusters of a certain size before forming a static charge to repel each other...

If the gold in solution is a colloid it has already been reduced to metal.it cannot be reduced again by another reducing agent like SMB, it cannot be reduced again by adding stannous chloride. 

If there is gold in a solution that has not been reduced, then yes you can reduce it to the metal with stannous chloride and get the violet color in the reaction.

So you can have gold colloids and you cannot reduce them in the stannous chloride test.
You can have gold chloride ions which can be reduced with stannous chloride, along with gold colloids that cannot be reduced.


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## saadat68 (Jan 28, 2019)

> . If there is gold in a solution that has not been reduced, then yes you can reduce it to the metal with stannous chloride and get the violet color in the reaction.


Thank you butcher 
Excuse me why do you and others said in another topics that we can't test colloidal solution with stannous chloride?
As you say if we have gold chloride in solution we can test it with stannous and it will reduce golds and shows purple color

*Edite: I think got it. *
1- A solution with gold colloides and gold chloride: stannous test will be purple
2- A solution with gold colloides and without gold chloride: stannous test will be purple or negative. Depends on colloides size

Are these right?


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## butcher (Jan 28, 2019)

You can not use stannous chloride to test for colloidal gold.
Just as you cannot use a drop of stannous chloride solution on a coin or a bar of gold-colored metal to test to see if it is gold, the stannous chloride will not react with the elemental gold metal to give a violet color.
Colloidal gold is elemental metal it will not react with stannous chloride.

The stannous chloride in the testing of a gold chloride solution, in the spot test the tin salt will reduce the gold chloride to elemental gold metal which forms a gold colloid solution, giving us a visual color as an indication of gold in solution.


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## saadat68 (Jan 29, 2019)

Is this correct? (Yes or no is enough. thanks)

*A solution with gold colloides and without gold chloride: stannous test will be purple or negative. Depends on colloides size

*


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## anachronism (Jan 29, 2019)

Sadaat.

Butcher explained why the test is negative in his post above.


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## saadat68 (Jan 29, 2019)

Yes I know. I am sorry but my question is: 
What happen when we mix a drop of gold colloides solution (without any gold chloride) with drop of stannous chloride in spot plate? Does it sometimes shows purple and sometimes not?

Can you say which is correct?
https://cdn3.imggmi.com/uploads/2019/1/29/ddabeb4ea64b374be31e96403c659786-full.jpg


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## Dr.xyz (Jan 29, 2019)

If there's no gold chloride and only colloidal gold, testing with stannous has no effect on solution colour, it stays what it was before testing.


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## anachronism (Jan 29, 2019)

Dr.xyz said:


> If there's no gold chloride and only colloidal gold, testing with stannous has no effect on solution colour, it stays what it was before testing.



Yes, as Butcher said above. Maybe Saadat missed it the first time around.


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## butcher (Jan 29, 2019)

Copperas (FeSO4) will reduce gold from a gold chloride solution, the crystal of ferrous sulfate will make a brown ring of precipitated gold in the spot test. Here the gold is reduced to metal as a brown precipitant.

Ferrous sulfate will not detect colloidal gold, the colloidal gold is already a reduced metal swimming in the in solution, the colloidal gold already has a full shell of electrons, copperas will not be oxidized by the gold colloid.

saadat68,
I may not be very good at explaining this to you, my goal is to try and explain it as I understand it, which may be harder for you to understand, Hope this helps, if not maybe someone else can put it into words you can understand better.

For these tests to work we have to be able to reduce the gold or change the gold from being gold ions to being gold metal.
Gold colloids are metal, a small cluster of gold atoms with a full shell of electrons, and cannot be reduced (Unless the colloid bond is broken from its static charge).

The gold chloride can be reduced to metal in these tests, the gold shares its only electron with three chlorine ions to form a salt of gold and chlorine dissolved in water, in the test of stannous chloride or copperas the gold is given back its electron, and reduced to metal, giving us a color indication of the reaction.

Free oxidizers like nitric chlorine... will also keep these tests from working as we cannot reduce the gold back to metal.


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## saadat68 (Jan 29, 2019)

Dr.xyz said:


> If there's no gold chloride and only colloidal gold, testing with stannous has no effect on solution colour, *it stays what it was before testing.*


Got it. 8) 
What a mistake.I am foolish sometimes. :mrgreen: butcher tried say this to me but I didn't understand. Sorry 
Even if colloidal gold be purple, It will shows purple on spot plate before adding stannous. 
So actually stannous chloride doesn't effect on colloidal gold.

Thanks all


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