# Extremely light silver chloride



## JonMiller (Nov 21, 2013)

ive run into a bit of a head scratcher with this material iam trying to refine. Its a material that consists of %11 silver, %70 copper, %10 tungsten powder , %5 nickel and the remainder is zinc and iron. 

I dissolved the material fully in nitric then filtered the solution . I then did 10 different tests in 50 ml test tubes. each one adding different amounts of salt i.e 5g,6g,7,g etc. 


The silver precipitates out great however it does not ball up or have a "cottage cheese" effect like my other alloys ive refined. It just precipitates very quickly and turns to 
a very light powder and only slightly settles. Unlike the other silver alloys ive done where it clumps up and falls to the bottom. 


What would your educated guess be to why this is happening. Too much free acid? tungsten powder maybe?


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## Palladium (Nov 21, 2013)

Its according to how concentrated the solution is.
Like the difference between 1 gram/10ml or 1 gram/100 ml.


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## MysticColby (Nov 21, 2013)

do the different salt concentration test tubes have different silver chloride behaviors? like 5g = very light and 10g = settles within minutes?


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## Westerngs (Nov 21, 2013)

Add a drop of nitric acid to each test tube and shake the heck out of it. Come back and tell me what happens to the silver chloride in each test tube.


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## JonMiller (Nov 21, 2013)

MysticColby said:


> do the different salt concentration test tubes have different silver chloride behaviors? like 5g = very light and 10g = settles within minutes?




No it's about the same no matter what amount I add anywhere between 3-10 grams. 

Iam going to try the extra acid test and see how that goes.


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## Palladium (Nov 21, 2013)

It's not the salt concentration that is going to make the difference. It's the silver concentration. You can add as much salt as you want and their is only so much silver that it can precipitate before the silver is depleted and you are just throwing salt at it. The difference is the silver concentration. The process you are talking about is nucleation. This is the same process we use to precipitate gold from solution. Precipitate gold from a weak solution and it comes down fine as powder and doesn't want to settle in part to the small atomic particle size and the interaction of van der Waals' forces. Precipitate gold from a concentrated solution and you will have larger atomic structures which leads to larger crystal growth and quicker settling times.


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## Palladium (Nov 22, 2013)

The (low) solubility of AgCl is reduced by the excess of Ag+ which is added, pushing the equilibrium to the right. We can further decrease the solubility by decreasing the temperature of the solution by using an ice bath.

Mechanism of Precipitation

After the addition of the precipitating agent to the solution of the ion under analysis there is an initial induction period before nucleation occurs. This induction period may range from a very short time period to one which is relatively long, ranging from almost instantaneous to several minutes. 

After induction, nucleation occurs, here small aggregates or nuclei of atoms form and it is from these "clumps" of atoms that the crystals which form the filtrate will grow. These nuclei may be composed of just a few atoms each so there may be up to 1010 of the nuclei per mole of precipitating product. As these nuclei form ions from the solution (which at this point are in excess) congregate around them. For example if hydrochloric acid were added very slowly to a solution of silver nitrate, silver chloride nuclei would form and silver ions (which would be in excess relative to Cl- ions) would congregate around them. 

In addition to the primary adsorbed silver ion, there are some nitrate ions aggregating further from the AgCl nucleus. These are counter ions and tend to aggregate around the [AgCl:Ag]+ center because these centers have a net positive charge (excess Ag+) and additional negative charge is required to maintain electrical neutrality. The counter ions are less tightly held than the primary adsorbed ions and the counter ion layer is somewhat diffuse and contains ions other than those of the counter ions. These layers of charges are known as the electric double layer.

Nucleation is a process in which
a minimum number of atoms, ions,
or molecules join together to give
a stable solid.

Adsorption is a process in which a 
substance (gas, liquid, or solid) is 
held on the surface of a solid. In 
contrast, absorbtion involves the
retention of a substance within the
pores of a solid.

The electric double layer of a colloid
consists of a layer of charge absorbed
on the surface of the particles and a 
layer with a net opposite charge in the
solution surrounding the particles.

A colloid is a solid made up of 
particles having diameters less 
than 10-4 cm.

http://www.chem.tamu.edu/class/majors/tutorialnotefiles/gravimetric.htm


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## Palladium (Nov 22, 2013)

Looking at this thread again i wonder to myself how many people actually realized the answers i gave in this thread explains a whole lot more than just the silver problem asked?


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## butcher (Nov 22, 2013)

I did and I really appreciate your posting it.


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## g_axelsson (Nov 23, 2013)

This is a really good explanation of the precipitation process. Thanks for posting it!

Göran


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## kadriver (Nov 26, 2013)

Palladium said:


> This is the same process we use to precipitate gold from solution. Precipitate gold from a weak solution and it comes down fine as powder and doesn't want to settle in part to the small atomic particle size and the interaction of van der Waals' forces. Precipitate gold from a concentrated solution and you will have larger atomic structures which leads to larger crystal growth and quicker settling times.




I often wondered why my gold precipitates as fine powder and takes a long time to settle one time, them clumps together nicely and settles quickly the next. Solution concentration is the key.

I'm still just an advanced beginner.

Palladium, your post about precipitation is most excellent, thank you.

kadriver


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## kadriver (Nov 26, 2013)

JonMiller said:


> ive run into a bit of a head scratcher with this material iam trying to refine. Its a material that consists of %11 silver, %70 copper, %10 tungsten powder , %5 nickel and the remainder is zinc and iron.



I could not find tungsten on my electromotive series chart, but the other listed metals would get left behind if the silver were to be cemented out using copper.

If JonMiller were to use copper to cement out the silver instead of precipitating the silver chloride, would the tungsten present a problem? Would the tungsten cement out onto the copper along with the silver?

I have no experience, that I know of, with tungsten.

Thanks

kadriver


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## goldenchild (Nov 26, 2013)

I wonder if using HCL instead of salt would solve some problems.


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## butcher (Nov 26, 2013)

Here they show tungsten (W) below copper in the reactivity series of metals.

I am not sure but I believe for some reason that tungsten is very reactive towards oxygen, although not oxidized in ordinary air at normal temperatures, but it can be dissolved into hydrogen peroxide, I think it is this reaction with oxygen that actual makes tungsten such a non reactive metal to be attacked by acids, metal that easily forms an oxidized coating on its outer layer making it difficult for acids to attack, or get through the oxide coating, but then again this is just a guess on my part. 

http://en.wikipedia.org/wiki/Reactivity_series

Now whether copper would reduce tungsten from solution can depend on if tungsten was in solution, also its state, with some metals sometimes when the metals are very close together in series it is difficult for one to replace the other from solution (maybe not far apart enough for that electron to want to move from the metal to the ion).

So I cannot say whether copper would (cement) or reduce tungsten from solution, that is if tungsten was even in that solution to begin with.
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Found this on the electrode potential of tungsten (electrolysis in cells, a comparison to the hydrogen electrode).
http://en.wikipedia.org/wiki/Standard_electrode_potential_%28data_page%29


WO2 (s) + 4OH(+) + 4O e(-) <--> W(s) + 2O H2O _______-0.12V 
WO3(aq) + 6H + 6e(-) <--> W(s) + 3H2O_______________-0.09
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The standard electrode potential is normally related to electrolysis, where the reactivity series of metals is normally related to the oxidation and reduction of metals in a chemical reactions, although both of these are similar they can also be different.

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When we look at the standard electrode potential (comparing to the standard hydrogen electrode potential) a metals or metal-salts electrode potential, We also have to keep in mind the metals or salts or state in solution, and the state of oxidation or reduction. (I am unsure how to say this).
lets look at lead:
PbSO4 + 2e(-) <--> Pb + SO4 _______-0.358V
Pb(++) + 2e(-) <--> Pb_____________-0.13V
Pb(++++) + 2e(-) <--> Pb(++) _______-0.169V


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## kadriver (Nov 27, 2013)

Great chart Butcher, I should have thought to look up reactivity series instead of electromotive series - Thanks

Since it is below copper, then tungsten may be a problem as it could possibly cement out with the silver onto the copper.

This is good to know should I ever come across any silver that is alloyed with tungsten.

I think Oz had some experience with tungsten and silver - wish he was around to share his wisdom.

kadriver


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## butcher (Nov 27, 2013)

Tungsten can be attacked in H2O2, dissolution rate is proportional to H2O2 concentration (as in the formula posted above.
This can give us a way to separate silver.

Another nice feature about tungsten, is that it is resistant to nitric acid (even hot and concentrated), but if hot and very dilute nitric will attack tungsten but very slowly.

This can also be used to help separate he tungsten from the silver.

I also believe I have seen some reactivity series charts with tungsten higher than copper in the series (I am not sure if I could find these charts again, and I am unsure of details).

As we know tungsten is a less reactive metal in many acids than copper is, but once dissolved into acid (base or H2O2...) it is no longer tungsten metal but an oxide or salt (ion of tungsten), so how that reacts in a chemical process like cementing it out with copper, I would have to do more study on, or try some of those small Hoke's like getting acquainted experiments to learn more.


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