Silver digested in Nitric Acid, silver nitrate question

[NobleMetalWorks]

I digested 5 ounces of silver in 200 ml of nitric acid. I expected the silver to dissolve into solution, then when the solution cooled, for it to form crystals of silver nitrate on the bottom. What happened was very different.

Here is a video of the results after the solutions stopped generating nitrogen dioxide gas.

EDITED: There is still nitrogen dioxide in solution, it's what gives the solution that yellow/gold color. The solution will become clear as nitrogen dioxide forms gas, but still be very careful and keep in a well ventilated area.

EDITED: I tried to use the youtube tags, twice, but it did not take so I provided a link instead.

https://www.youtube.com/watch?v=Odav4VZroCc

You can see crystals on the bottom, and crystals falling towards the bottom as they sparkle (I wish I took the video before, it was really something to see).

I added the nitric acid to silver shot, and heated to 160 degrees for 30 minutes. The silver dissolved pretty readily. The results however were not what I expected. As the reaction evolved a white cloudy substance immediately was produced and started settling to the bottom. Mind you, the heat plate was on, the nitric acid was hot, and silver nitrate crystals (or what I assume to be so) were already falling out of solution. I thought in order for the silver nitrate to accumulate it would do so only after the solution cooled.

This is my first time making silver nitrate, and I want to make sure that I didn't do something other than I intended. Because my results were unexpected I am posting this here in the hopes someone might be able to explain what happened, why, and how to correctly make Silver Nitrate.

Thanks

Scott

 

[goldsilverpro]

You should have dissolved the silver with a 50/50 mix of nitric acid and distilled water. It will work faster, more efficiently, and you won't get any crystals. To dissolve the crystals you have produced, add some distilled water and heat.

 

[Westerngs]

You made a supersaturated silver nitrate solution, that is why crystals formed when still hot.

I don't remember the solubility of silver nitrate in hot water, but I will look it up later. You passed that point.

 

[NobleMetalWorks]

You should have dissolved the silver with a 50/50 mix of nitric acid and distilled water. It will work faster, more efficiently, and you won't get any crystals. To dissolve the crystals you have produced, add some distilled water and heat.

Actually I do want crystals, I will mill them and use the silver nitrate in another process.

I was expecting all the silver to dissolve into solution, and then to make small additions of silver until all the nitric acid was exhausted, then to allow the solution to cool and the gas to escape, then when the solution was cool the crystals would form on the bottom. I would then evaporate off the rest of the solution, dry out the silver nitrate and mill it.

What actually happened is that once I applied the heat, the silver started making a foaming white thick precipitant and of course evolved gas, but at no time was all the silver digested into solution so that it was clear, it was a milky yellow color, then the crystals immediately started to form and fall to the bottom like sponge, before solution was ever taken off the heat. Once it was taken off the heat, the crystals really started to form and fell out of solution over the next 30 minutes or so.

So I didn't get the expected result, and I didn't get it when the solution started cooling. The silver nitrate that precipitated was fine crystals that acted more like sponge.

Scott

 

[NobleMetalWorks]

You made a supersaturated silver nitrate solution, that is why crystals formed when still hot.

I don't remember the solubility of silver nitrate in hot water, but I will look it up later. You passed that point.

So for my intended purpose, which is to take the silver nitrate crystals and mill them for use in another process, super saturating actually worked to my benefit? Or am I missing something?

Scott

 

[Lou]

Pure nitric acid acting on fine silver is relatively inefficient. The acid is too oxidizing so some of the silver may transiently form Ag2O and the rate of attack be slowed. Believe it or not, dilute it some and it'll work better and faster. The same is true of mercury, and also copper.

The milkiness may be due to glassware that isn't scrupulously clean--it is very, very difficult to remove all chlorides from the surface of glass, even with repeated DI rinses!

You will be better served to use a 50/50 mix, boil that down into a concentrated solution and then pour into a chilled plastic tray or stainless pan. Bake than under low heat until dry, then ball mill it.

Alternatively, you can just pour the solution into a stainless steel pot and then evaporate to dryness, melt, and pour onto a stainless sheet.

 

[NobleMetalWorks]

Pure nitric acid acting on fine silver is relatively inefficient. The acid is too oxidizing so some of the silver may transiently form Ag2O and the rate of attack be slowed. Believe it or not, dilute it some and it'll work better and faster. The same is true of mercury, and also copper.

The milkiness may be due to glassware that isn't scrupulously clean--it is very, very difficult to remove all chlorides from the surface of glass, even with repeated DI rinses!

You will be better served to use a 50/50 mix, boil that down into a concentrated solution and then pour into a chilled plastic tray or stainless pan. Bake than under low heat until dry, then ball mill it.

Alternatively, you can just pour the solution into a stainless steel pot and then evaporate to dryness, melt, and pour onto a stainless sheet.

Thank you Lou,

I think the milkiness was because of the aggressive reaction. Because of all the gas that was evolving, I think it foamed in solution, while silver nitrate was falling out of solution.

I'll add water and see where it takes the reaction..

Thanks again for everyone that posted on this, I love this forum...

Scott