masonwebb,
When a metal like gold is dissolved into solution the metal has to be oxidized (oxidize this means an electron has to be removed from the atom of gold metal), the gold is free now to join with a chloride in solution (from our HCl acid).
Nitric acid or chlorine are strong oxidizers, and they will take electrons from the gold (so that the gold is oxidized into solution as a chloride salt of gold dissolved into solution).
This gold atom having lost an electron becomes a positive ION (Cation), the reduced chloride in solution is the Anion, these bond together to form a dissolved salt of gold in solution we call gold chloride.
To get the gold to change back into a metal (in our case a precipitate of brown gold powder) we have to reduce the metal (reduce means to gain back an electron), we use a reducing agent like ferrous sulfate or sodium metabisulfite to reduce our gold (give the gold ion an electron so it becomes a gold metal atom again.
Another metal Higher in the reactivity series of metal can also reduce our gold from solution, a metal like copper which has all of its electrons wil give our gold ion an electron and the copper (losing its electron) is oxidized into solution as a copper ion (now copper chloride solution).
Tin chloride solution (tin metal dissolved in HCl) called stannous chloride, that we use to test for gold will reduce metals like gold, when we use stannous chloride to reduce our gold back to metal it forms a violet color of colloidal gold, this colloid of gold is very fine particles of gold metal with different charges positive and negative, this colloid keeps the gold constantly moving in solution as these charged particles of gold keep shoving each other around in solution and will not settle out of solution, we use this as a test for gold, the violet color of stannous chloride reacting with gold is an extremely sensitive test, the color reaction will occur with very little gold in solution.
The stannous chloride has to be able to reduce the gold back to metal before we can see the violet color (even if there is gold in solution), in order for this to happen we cannot have free oxidizer in solution (like chlorine, nitric acid ETC.) as these will either keep the gold oxidized or re-oxidize the gold so that it will not show up in our test.
So if we do have gold in solution and we have free oxidizer the stannous will not turn a violet color (positive for gold), or it may turn violet for a brief period and then redissolve and our violet color disappear, so here we can use this to help us determine if we have removed or used up our oxidizer in solution.
We will not be able to reduce the gold back to metal (precipitate the gold from our auric chloride solution) if we still have free oxidizer in solution, with our reagent (SMB, ferrous sulfate or other gold reducing chemical) cannot give gold back that electron and make the gold fall to the bottom of our vessel as brown powder if the oxidizer in solution keeps taking away the electrons, which we are trying to give it back.
I know I am giving you a little bit of a hard time, but I did not think you would learn if I did not.
Just because you seen gold dissolve into solution, it does not mean you have gold in solution.
let’s say I dissolve gold from a mixed bunch of powders I know has gold in the powders, (and there is another metal in these powders also), yes the gold will dissolve, but so will some of these other metals, and if there is free metals in the mix (metals with all of their electrons in there atom), guess what happens, the metal lower in the reactivity series of metals (look this up and study), will give an electron to the gold (this gold now is reduced back to metal and comes back out of solution, as the other metal lower in series replaces the gold in solution, now even though we seen the gold dissolve into solution this solution very well could contain very little or no gold in solution (the solution could even be colored to look like a gold solution a nice yellow color of iron in solution, we cannot see our gold any where, and we may THINK it is solution but it may not be, unless we test for it we may have just lost our gold, thinking it is someplace it is not (and believing it is not someplace it is we can very easily throw out our gold and then stand there scratching our head wondering what happened how come we cannot precipitate gold from the solution we KNOW has gold in we saw it dissolve.
You are a good sport, but you do not know where your gold is at until you get your stannous chloride, your stannous chloride can also help you to determine if you still have free oxidizers in solution, if stannous cannot reduce your gold it is very probable that SMB will not be able to reduce your gold.
I hope I could explain this so you will be able to understand the importance of your stannous test, so that you do not just assume you know where your gold is at, but that you will use your eyes (stannous chloride SnCl2) to be able to see where your gold is at, this way you are not working blindfolded.
That should be sticky'd for other people to read. So if chlorine is the oxidizer, heating the solution will drive it out!. I really wish I would have kept the contents that I filtered out. I should have washed everything in hcl several times before starting this. I think this whole situation could have been avoided. But then again I wouldn't have learned so much, so thank you Butcher!
