Product of HNO3 and NaCN?

[venom...@gmail.com]

I'm attemping to plate using platinum, and I'm currently on the first
step, bringing platinum metal into solution. My idea was to use aqua
regia, with some NaCN to complex with the platinum and help bring it
into solution, however upon adding my NaCN to the aqua regia, two
things happened. One, a white gas evolved, I'm not sure if this was
just water vapor, or it was something worse like HCN. Secondly, my
solution turned brown, and there are strange brown round shaped
precipitates. There are several of them in the beaker, and they all
have a similar shape, so I'm guessing it's some kind of crystal, though
I can't imagine what it could be. The only ions that should be in the
solution in any great amount are H+, Na+, CN-, Cl-, and NO3-. As far as
I know, all of those are soluable.
I then tested what happened if I added NaCN to HNO3 and HCL by
themselves, and the HCL did not react, but the HNO3 then, and formed
the same odd precipitate and white gas. The odd part is I've added KCN
to HNO3 before, and nothing happened, and I'm not sure why sodium would
do something like this.
Any insights are greatly appriciated.

[Madalch]

Never, ever add any cyanide to a solution of acid. Cyanide is a
relatively strong base, and will form HCN in acidic solution. HCN will
not form a complex with any metal, but it is volatile and toxic.

That being said, organic cyanides can be hydrolyzed in acidic solution
to give amides- possibly the HCN is reacting to give CO2 and ammonium
nitrate.

But if you want to dissolve platinum, either use aqua regia by itself,
or cyanide in a BASIC solution (as in shoutingly not acidic, not as in
the programming language) with a different oxidant. Or just buy some
platinum salts.

Who sells cyanide and aqua regia to people who are daft enough to mix
them?

[venom...@gmail.com]

Well the aqua regia was made by me. But besides that, HCL and HNO3 do
not form HCN with cyanide. The most common acid that will form HCN is
HSO4. I'm thinking my HNO3 might actually be comtaminated, but I'll
have to run some more tests tomarrow.

[Madalch]

Any acid in aqueous solution will give HCN. Check a table of Ka
values, and realize that hydronium ions don't give a damn where they
come from. Whether the HCN stays in solution or evaporates depends on
how much you add.

[venom...@gmail.com]

I've added a lot of KCN to a small amount of aqua regia, and have never
gotten HCN gas, and have added a tiny bit of KCN to HSO4, and have
gotten gas immediately. I'm not sure why this happens, but that is what
I have observed.

[Borek]

Most probably in aqua regia cyanides are oxidised before the HCN
can evolve. Still, if you plan to add more cyanides to acidic solutions
at least please check that you are alone, so that you will kill only
yourself.

BTW, sulfuric acid is H2SO4, not HSO4.

Best,
Borek
--
http://www.chembuddy.com - chemical calculators for labs and education
BATE - program for pH calculations
CASC - Concentration and Solution Calculator
pH lectures - guide to hand pH calculation with examples

[Uncle Al]

venom...@gmail.com wrote:
>
> I'm attemping to plate using platinum, and I'm currently on the first
> step, bringing platinum metal into solution. My idea was to use aqua
> regia,

Look it up. When the natural alloy of platinum, palladium, osmium,
and rhodium is digested with aqua regia, the palladium and platinum
dissolve and are extracted as a solution of chloropalladic acid and
chloroplatinic acid. Platinum is then precipitated from this solution
as ammonium chloroplatinate.

> with some NaCN to complex with the platinum and help bring it
> into solution,

Holy shit. Holy fucking-a shit.

> however upon adding my NaCN to the aqua regia, two
> things happened. One, a white gas evolved, I'm not sure if this was
> just water vapor, or it was something worse like HCN.

HCN, ClCN, stuff like that.

> Secondly, my
> solution turned brown, and there are strange brown round shaped
> precipitates.

CN- doesn't like oxidizing agents and moisture. KCN decomposes in
air, albeit slowly.

[snip]

> I then tested what happened if I added NaCN to HNO3 and HCL by
> themselves,

Holy shit. Holy fucking-a shit.

> and the HCL did not react, but the HNO3 then, and formed
> the same odd precipitate and white gas. The odd part is I've added KCN
> to HNO3 before, and nothing happened, and I'm not sure why sodium would
> do something like this.
> Any insights are greatly appriciated.

Look up the chemistry of platinum.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

[venom...@gmail.com]

That still doesn't explain why this happens with NaCN and not KCN
though, any ideas on that?

[venom...@gmail.com]

No one has been able to identify the precipitate, anyone have any ideas
at least.

And I'm doing everything in a fume hood, and wearing a gas mask (that
is rated for HCN), so I'm not really that worried about my safety.

[Tom]

Uncle Al wrote:

> Holy shit. Holy fucking-a shit.

You gotta love Uncle Al. He is telling you the truth.

[Uncle Al]

A forced air ventilator might be adequate. Only a fool trusts a
passive mask. HCN goes through skin. The fume hood exits into your
breathing air, and rather close to home unless its motor is external
to the building and all intervening ductwork is under negative
pressure. At least HCN is ligher than air - but not by much.

If you are working with HCN you need a co-worker who smokes tobacco.
Sub-lethal HCN dose imparts a characteristic unpleasant taste to
tobacco users. Some smokers don't taste it. Drag out that body and
try another one.

Uncle Al knows a guy who sprinkled KCN onto hot metal for case
hardening - by hand. One presumes Social Security is going to lose a
bundle on him.

[Mark Thorson]

Uncle Al wrote:

>
> venom...@gmail.com wrote:
> >
> > with some NaCN to complex with the platinum and help bring it
> > into solution,
>
> Holy shit. Holy fucking-a shit.
>

> > I then tested what happened if I added NaCN to HNO3 and HCL by
> > themselves,
>
> Holy shit. Holy fucking-a shit.

C'mon, Al. The guy's an obvious troll.
Please don't encourage him by taking the bait.

[Wilco Oelen]

I have tried to repeat your observations and I succeeded partially.
This indeed is a remarkable reaction.

@Uncle Al: I'm still alive after this experiment and still feel good :)
I have taken safety measures with the cyanide. All experiments were
done with wind from behind (we have a lot of wind this day :))

I made some aqua regia from 60% HNO3 and 30% HCl and allowed this to
stand for half an hour. This gives te familiar yellow color of aqua
regia.

I added some solid NaCN to the test tube, containing the aqua regia.
The solid, which enters the liquid remains white and hardly dissolves.
A very small amount of gas was evolved. The solid, sticking to the wet
glass, however, turned brown, almost black within a few minutes. The
color went as follows: white --> yellow --> orange --> brown -->
brown/black.

Here follows a picture of the test tube with the black stuff, sticking
to the glass. This brown stuff is NaCN, transformed into something
brown.

http://woelen.scheikunde.net/science/chem/riddles/cyanide+nox/exp0001.jpg

A close-up of some of the brown stuff

http://woelen.scheikunde.net/science/chem/riddles/cyanide+nox/exp0002.jpg

When some of the brown stuff is scraped from the glass and dissolved in
water, then a brown solution is obtained. The brown stuff easily
dissolves:

http://woelen.scheikunde.net/science/chem/riddles/cyanide+nox/exp0003.jpg

Finally, the following picture shows what happens to the contents of
the test tube, when a lot of water is added to the aqua regia and the
brown stuff is allowed to dissolve. At this point, a lot of small
bubbles of gas are produced. The piece of white NaCN at the bottom also
dissolves and gives small bubbles of gas. All this is shown in the
final picture:

http://woelen.scheikunde.net/science/chem/riddles/cyanide+nox/exp0004.jpg

If any of you has an explanation for this, then that would be very
nice. So, the OP, indeed did find something special.

I have no KCN, but I expect that the outcome will be approximately the
same. The difference to my opinion is not in NaCN or KCN, but in the
way, it is added. The solid, immersed in the acid does not turn brown
at all.

When this experiment is repeated with NaCN, sticking to glass, above
30% HCl, then no brown color is produced. As soon as some NaNO2 is
added to the HCl, then NOx is produced (NO, NO2 and NOCl) and then the
NaCN, sticking to the glass becomes brown at once, and also quite some
heat is produced at the solid NaCN. So, apparently there is a reaction
between the NOx and the solid NaCN.

[venom...@gmail.com]

Excellent explanation Wilco. That is pretty much exactly what I
observed as well, but explained much better. :-P
And as for the fume hood I'm using, it's in a university lab, and
poeple have done much more dangerous experiments then I am doing in
this lab before, so as I said, I am not that worried.

[rek...@gmail.com]

Cyanide is oxidized by NO2 to form cyanate. I suggest the solids are
oxidizing to sodium cyanate on the tube walls, which will redissolve
easily in aqua regia. The vapor from dissolved solid is HCN.

[venom...@gmail.com]

Anybody have any ideas as to the identity of this substance?

[Ron Jones]

Probably correct. Cyanide is easily oxidised to cyanate- it's the first
step of destruction with bleach : cyanide to cyanate, complete in under one
hour, then up to 24h (dep on temp) to fully oxidise to N2 and CO2.

And I agree with the others - any acid + cyanide gives HCN - *but* don't
forget it's 4% water soluble, so a small amount may not gas off straight
away.

--
--
Ron Jones

Don't repeat history, see unreported near misses in chemical lab/plant
at http://www.crhf.org.uk
Only two things are certain: The universe and human stupidity; and I'm
not certain about the universe. ~ Albert Einstein

[venom...@gmail.com]

Ron Jones wrote:
> rek...@gmail.com wrote:
> > Cyanide is oxidized by NO2 to form cyanate. I suggest the solids are
> > oxidizing to sodium cyanate on the tube walls, which will redissolve
> > easily in aqua regia. The vapor from dissolved solid is HCN.
>
> Probably correct. Cyanide is easily oxidised to cyanate- it's the first
> step of destruction with bleach : cyanide to cyanate, complete in under one
> hour, then up to 24h (dep on temp) to fully oxidise to N2 and CO2.
>
> And I agree with the others - any acid + cyanide gives HCN - *but* don't
> forget it's 4% water soluble, so a small amount may not gas off straight
> away.

I have one problem with that theory. Where is the NO2 gas coming from?
As far as I know, HNO3 does not readily decompose to NO2, even in the
presence of HCl. Or am I wrong?

[Farooq W]

Wilco,

May I suggest something like nitrosyl cyanide NOCN an analogue of
nitrosyl chloride (which imparts a yellow color to aqua regia). Google
shows that this compound does exist but I do not know anything of its
color or stability. Is the observed brown color permanent or fleeting?

[venom...@gmail.com]

Aqua regia is yellow just by itself. And in my experience, the brown
color is permanent. My solution has been the same brown color for a
week now.

[Wilco Oelen]

Ron Jones wrote:
> rek...@gmail.com wrote:
> > Cyanide is oxidized by NO2 to form cyanate. I suggest the solids are
> > oxidizing to sodium cyanate on the tube walls, which will redissolve
> > easily in aqua regia. The vapor from dissolved solid is HCN.
>

I can imagine this explanation, but is cyanate brown???? I always
though that cyanate is a colorless anion and that solid cyanates are
white.

Indeed, in the meantime I found out that NO2 is responsible for the
color. When I add NaNO2 to some acid and I put some solid NaCN in the
brown gas, then it very quickly turns brown and it remains brown. Quite
some heat is evolved also. The solid NaCN with the brown stuff becomes
really hot in NO2-gas of higher concentration.

NO2 also is produced in small amounts by ripened aqua regia (together
with NO, NOCl and Cl2), so with this part of the explanation I can
agree.

But what still puzzles me is the brown solid. So, apparently it is a
reaction product of NaCN and NO2, but its composition still is a
mystery to me.

[Wilco Oelen]

Nitrosyl cyanide (ON-CN) is a blue gas. So, this brown stuff definitely
is not nitrosyl cyanide. It is said, that it can be made by passing
ONCl over AgCN, but I never tried to do this personally. I've not
observed any blue gas in my experiments. If I had such a special thing,
then I certainly would have noticed it :)

The brown color is permanent. Dilute solutions of the brown stuff in
water remain brown (at least for a day or so, after that period I
discarded the solution).

I made a more through description of what I did and I put this on my
chemistry website:

http://woelen.scheikunde.net/science/chem/riddles/cyanide+nox/index.html

Hopefully this description helps resolving this riddle. There are some
subtle details on the behavior, depending on how wet the solid actually
is.

[Farooq W]

-------------------------------------------------------------------------
Before attempting to discuss the original problem, Cu(II)-thiosulfate
reaction caught my attention. The questions were.

What is the yellow precipitate?

Most likely colliodal sulfur. Copper sulfate is intrinsically acidic
and you know any acid as weak as "carbonic acid" can initiate sulfur
precipitation. The dissolution of yellow precipitate is indeed complex.
Just check if sulfur has the property of dissolving in concentrated
thiosulfate solutions

What is the colorless compound, when excess sodium thiosulfate is
added?
Could be Cu(I) and different polythionates.

Is the dark compound indeed copper (II) oxide or copper (II) sulfide?
Most likely. As you say it takes time for blackening. Did you try to
isolate it?
-------------------------------------------------------------------

Coming to the main topic: Some suggestions, if you have elaborate
glassware system with safety of course. Can you simply pass first pure
NO2 on moist salt (or try a dry one) in _separate_ test tube. Dry the
gases if more accuracy is required to confirm that this is really a
solid phase reaction. Similarly try generating NO and pass the gas over
it. This will clarify which NOx causes the brown color generation. One
can try *pouring* NO2 in another test tube and stopper it.

Secondly search about azulmic acid, which is browm and polymeric form
of HCN. Apparently aqueous soln. of cyanogen forms this substance.

[Wilco Oelen]

Farooq W wrote:
> -------------------------------------------------------------------------
> Before attempting to discuss the original problem, Cu(II)-thiosulfate
> reaction caught my attention. The questions were.
>
> What is the yellow precipitate?
>
> Most likely colliodal sulfur. Copper sulfate is intrinsically acidic
> and you know any acid as weak as "carbonic acid" can initiate sulfur
> precipitation. The dissolution of yellow precipitate is indeed complex.
> Just check if sulfur has the property of dissolving in concentrated
> thiosulfate solutions
>
> What is the colorless compound, when excess sodium thiosulfate is
> added?
> Could be Cu(I) and different polythionates.
>
> Is the dark compound indeed copper (II) oxide or copper (II) sulfide?
> Most likely. As you say it takes time for blackening. Did you try to
> isolate it?
> -------------------------------------------------------------------

Continued in new thread on copper and thiosulfate....

>
> Coming to the main topic: Some suggestions, if you have elaborate
> glassware system with safety of course. Can you simply pass first pure
> NO2 on moist salt (or try a dry one) in _separate_ test tube. Dry the
> gases if more accuracy is required to confirm that this is really a
> solid phase reaction. Similarly try generating NO and pass the gas over
> it. This will clarify which NOx causes the brown color generation. One
> can try *pouring* NO2 in another test tube and stopper it.

This is a nice suggestion and I'll try it. Making fairly dry NO2 is not
that hard for me. Making NO without any traces of NO2 is a little
harder, because even the slightest amount of air makes NO2 already from
NO. A possible way might be to collect the gas under water, but then of
course the problem is how to get some NaCN in there, without making it
wet. I'll think about this.

> Secondly search about azulmic acid, which is browm and polymeric form
> of HCN. Apparently aqueous soln. of cyanogen forms this substance.

Wow, never heard of azulmic acid, but this may explain the
observations. What still remains to be resolved is how this can be
formed from an oxidative dry environment, but it certainly is worth
looking into.

[venom...@gmail.com]

Wilco, I have something else you may want to try. Add a small amount of
NaCN to a beaker/test tube containing only HCl. I'm not sure if
something went wrong, but I tired this, and after several days, I was
left with a black (or very dark brown) sludge. Can you try to verify
this?

[Wilco Oelen]

Do you mean aqueous HCl (hydrochloric acid, e.g. 30% by weight), or do
you mean dry gaseous HCl?
The first experiment I can do without any problem, the second needs a
little bit more preparation.

[venom...@gmail.com]

Haha yea sorry I should have specified that. I meant hydrochloric acid.
The acid I'm using is 12M, I'm not sure what that would be in percent
off-hand, but 30% should be fine.

[Farooq W]

> Haha yea sorry I should have specified that. I meant hydrochloric acid.
> The acid I'm using is 12M, I'm not sure what that would be in percent
> off-hand,

...around 36% :)

[Wilco Oelen]

I can confirm your observations. Adding solid NaCN to 30% HCl results
in a white chunk at the bottom (it does not dissolve). After a day, it
has turned brown. After a longer time it has become darker. The liquid
above the chunk remains colorless. I'll keep the sample for a little
longer in this state and then I'll shake it and see what happens. An
update on the result follows.

[venom...@gmail.com]

I'm going to try to perform an experiment to see if ANY of the NaCN
disolves in hydrocloric acid. It might take me a few days to get set up
(I'm planning to use a vacuum in a bell jar to evaporate the acid
because I don't want to heat the solution), but I'll post back here
with the results. Any input on the second experiement would be greatly
appriciated.

[Wilco Oelen]

Wilco Oelen wrote:
> I can confirm your observations. Adding solid NaCN to 30% HCl results
> in a white chunk at the bottom (it does not dissolve). After a day, it
> has turned brown. After a longer time it has become darker. The liquid
> above the chunk remains colorless. I'll keep the sample for a little
> longer in this state and then I'll shake it and see what happens. An
> update on the result follows.

The solid at the bottom is almost black now. The liquid above the
sample has become brown. Not a red/brown color like e.g. Br2-water, but
more like tea. It is however, completely clear and not a little turbid
like tea. it is just the color which coincides.
When the liquid is shaken, then some of the black stuff dissolves and
the liquid becomes somewhat darker, however, the solid does not
completely dissolve. This is to be expected, because NaCN probably at
first gives HCN and NaCl, the latter being almost insoluble in
concentrated HCl.