Nitric acid elemination

[sayf]

Thanks alot kurt and butcher u r a great help
One last question
When adding a drop of stannous chloride to aqua regia for gold test if the solution turns colourless (like water)
What does that indicate
I tried searching every where but i found no result

 

[butcher]

To me, it would indicate that either there is no gold in the drops of the solution of aqua regia being tested or that the stannous chloride is not able to reduce the gold ions into a colloidal gold reaction (possibly from too much oxidizer like nitric left in solution).

The color change to clear may be indicative of some kind of chemical reaction, like acid being oxidized or reduced or some other reactions such as metal ion being oxidized or reduced, but it does not indicate gold or anything of real interest.

 

[sayf]

Well, many thanks again butcher, spreading knowledge for free is a noble thing to do these days
U r the boss!!

 

[Yggdrasil]

Sayf
Just to make sure what you mean!
Adding a drop of Stannous to AR, you don't add the drop to the solution do you?
A spotplat or paper should be used
It was a bit unclear in your post, and that should not be done, because it converts the PMs to colloids and you will have to redissolve them.

Just asking to be sure

 

[butcher]

When you mentioned adding stannous to aqua regia, I had the feeling you were not talking about adding the stannous to a drop or two of the solution in the spot plat, drops of wetted on paper, or in a small test tube.
That is why I answered it the way I did, we only need to do the test on a small sample of the solution, we do not want to contaminate the whole batch of the solution by adding the reagent to it, doing so would not indicate gold but would contaminate the batch, lock up some gold in the solution making colloids and makeing recovery of that portion of gold extremely difficult to detect or recover...

 

[kurtak]

To clarify what butcher said

When you test a solution for gold you "do not" add a drop of stannous to the whole solution

instead you put a drop of the solution in a spot plate - or a plastic spoon - or in a test tube - or on a piece of paper towel - or on the end of a Q-tip

You then add a drop of stannous to the drop of solution as described above

if the solution you are test has gold in it - when you add the drop of stannous to the drop of solution you are test the test will turn purple (if there is just a little bit of gold in the solution) to almost black (purple/black) if there is a lot of gold in the solution

In other words - depending on the concentration of the gold in the solution (if there is gold in the solution) when you put the "drop" of stannous on the "drop" of solution --- it will turn purple or purple/black or black/purple

Kurt

 

[butcher]

The Stannous chloride test should show a violet color for gold with the reaction developing fairly immediately after mixing the solution and reagent.

SnCl2 can also reduce silver from a solution, but with a seeming delay of the reaction of the solution, initially with the solution being clear (then going with a milky with possibly precipitating a white substance) and then later the reaction turns violet as the silver is reduced by photons of light.

 

[sayf]

Yeah i surly add stannous to few drops of aqua regia not to the whole solution of course
Thank u guys for ur concerns