So i dissolved the base metals off some Ram fingers and processor cores with nitric acid and i now have a nice blue copper solution. I decided to test with stannous and i got a purple color that fades quickly. I can still see gold flakes in my solution but, did some dissolve or is my stannous going bad?
Purple color from stannous wrong?
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Golddigger76
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Try a drop of stannous on the a Q-tip where the stick and cotton meet and dip the end of the Q-tip in your solution and your results will be easier for you to read.
You can also put a drop of your solution on a filter paper and then put a drop of stannous on it.
I never cared for testing a solution in a dish. Just not clear enough for me and wastes pm bearing acids.
You can also put a drop of your solution on a filter paper and then put a drop of stannous on it.
I never cared for testing a solution in a dish. Just not clear enough for me and wastes pm bearing acids.
cejohnsonsr1
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Sounds like you have a little gold in solution. Purple is the color of the reaction for gold. When you see black, it’s just because the solution is very pregnant and produces a very strong reaction. It’s really still purple , but so deep that it appears black. I wouldn’t worry about it. That’s what your stock pot is for.
Agreed, I cringe every time I see someone stannous test in a plastic spoon. Filter paper/Q-tips are cheap and don't add plastics to the landfills. Q-tips/filter paper can go into filter storage and recover PM's it later.
Martijn
Well-known member
The reason it fades is probably some free nitric in solution. Edited: some free hcl in your nitric solution.
Stockpot or 'when doubt, cement it out'
Stockpot or 'when doubt, cement it out'
Excess HCl will not cause a stannous test to fade, but excess nitric will. You had it right the first time Martijn.
Dave
Dave
It's nitric
Nevermind i didn't see you said nitric lol.
Ok, the free nitric would make sense. I forgot that it says to use dilute nitric acid for base metals. So, maybe some gold already dissolved?
God, i wasted like 250ml of nitric acid
Wait, would that make sense? Why would it fade if the gold is in solution?
Ok, i tested again with qtip and negative. What's weird is i tested again just out of curiosity in the plastic cup and also negative. Is it possible that the gold precipitated back out by itself? Same stannous solution. Also last night i made another gold solution to test the stannous and it worked fine.
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Martijn
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I know, but it's more likely to have some 'free' nitric after a nitric digestion than HCl would be present. So a kind of reversed AR(..?) hence my correction. Both of my comments could be interpreted wrong
Noone pointed out whay the purple result disappeared.
Because the gold get redissolved.
Probably still some base metal fragments in there, causing the Gold to cement out.
Martijn
Well-known member
It's always a good idea to make a weak solution of gold chloride to test if your stannous works good. Just strong enough to see purple.
It sounds like you have nitric with some HCl in it or your beaker was not cleaned well enough before use, or you used chlorinated water to dilute the nitric.
The tap water I'm not completely sure of, but traces of chlorine will create weak AR in your nitric.
Again I am not sure if this is completely true: but i can imagine the stronger the AR is, the weaker the test result will be. And the faster it will redissolve.
Since you have the most gold foils still intact, I suspect you have very weak AR.
But testing it showed a mistake in your process somewhere. Now you can look for the source of the problem before you get into more problems with silver e.g.
Martijn.
How clean was your glassware and utensils? Small residues can create a weak AR at times. I have had positive results from using AP next to nitric on the same hot plate. The test results were very weak, and often questionable, but positive. A couple of times I have had HCl near a nitric digestion and get positive results in the nitric solution. Again very weak but a clear positive.
Keep things clean as possible and chemicals separated as much as possible.
Keep things clean as possible and chemicals separated as much as possible.
They could have been cleaner
