nimgoldman
Hazard to Others
Posts: 303
Registered: 11-6-2018
Member Is Offline
|
|
Silver nitrate giving off HCl ??
I've made silver nitrate the common way (dissolving silver metal in conc. nitric acid).
Once most of the silver nitrate crystallized, I poured off the water and left the crystals to dry.
I kept the little water and slowly evaporated it, yielding nice square crystals.
However, the crystals slightly yellowed and smell exacly like hydrogen chloride. The putrid smell managed to fill the entire storage room where it is
faintly smelly now (at first it smelled like something badly rotten).
Here are some hypotheses:
- the silver contained some chloride ions, maybe it was refined from silver chloride and some remained in the metal
- silver nitrate picks up something from the air and reacts with it
- the nitric acid (made from sodium nitrate and sulfuric acid) contained some impurities
- chloride ions could come from water used to make nitric acid - stupid me used just filtered water, not distilled
It's quite a bit of crystals so I think I will recrystallize them and measure pH of the remaining water to confirm presence of an acid.
Any suggestion where that HCl smell could come from would be welcome.
|
|
|
Sulaiman
International Hazard
Posts: 3558
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Offline
|
|
I've never associated HCl with 'putrid', sulphur compounds maybe.
The good news is that there is no copper in there- difficult to remove.
The first batch of crystals are clear/white with no odour ?
If so then re-crystalise the second batch leaving some liquid un-crystalized
- which will hopefully contain most of the contaminant(s)
CAUTION : Hobby Chemist, not Professional or even Amateur
|
|
|
DraconicAcid
International Hazard
Posts: 4278
Registered: 1-2-2013
Location: The tiniest college campus ever....
Member Is Offline
Mood: Semi-victorious.
|
|
Perhaps you're smelling NO2, which smells like bleach?
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
|
|
|
12thealchemist
Hazard to Others
Posts: 181
Registered: 1-1-2014
Location: The Isle of Albion
Member Is Offline
Mood: Rare and Earthy
|
|
NO2 sounds quite plausible to me. Acidic gases tend to have a similar type of odour, and people tend to seem to disagree about the smell of
particularly NO2. Trace amounts of nitric acid could lead to this odour. Either way, recrystallisation should fix the problem.
|
|
|
MrHomeScientist
International Hazard
Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline
Mood: No Mood
|
|
Agreed. Smell isn't a definitive way to identify something; everyone's nose is different.
The only possible source of chloride is from your filtered water, but unless you were filtering salt water this would be in only trace amounts. Plus,
even if there were chloride present, the silver would have precipitated it out as AgCl long before it could volatilize into anything smelly. You used
nitric acid, so the logical conclusion is nitrogen dioxide.
If you want to "calibrate" your nose, you could prepare a flask of HCl(g) and a flask of NO2 and smell each side-by-side. Remember to waft!
|
|
|
Herr Haber
International Hazard
Posts: 1236
Registered: 29-1-2016
Member Is Offline
Mood: No Mood
|
|
It depends what you are doing with that HCL.
Mix S + Fe and add HCL and you'll definitely get an egg smell.
That was the "do not cut corners" lesson around the time I was 14, trying to make a conductive cement (hence the iron).
I stupidly decided I would not go to the faucet and use any liquid instead. I chose vinegar :-/
Regarding chlorine I really dont believe the contamination comes from water or from your nitric acid distillation.
I dont really care about this when distilling acid or cleaning my glassware for silver and never had any problems.
|
|
|
Sulaiman
International Hazard
Posts: 3558
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Offline
|
|
S = Sulphur 
CAUTION : Hobby Chemist, not Professional or even Amateur
|
|
|
AJKOER
Radically Dubious
Posts: 3026
Registered: 7-5-2011
Member Is Offline
Mood: No Mood
|
|
Assuming that NO2 is the gas responsible for the smell. How could it be forming?
You may have created some elemental Ag, from light exposure at one point, which can reliberate electrons, e-, with more light (see http://www.nrcresearchpress.com/doi/pdf/10.1139/v73-375 ):
Ag + hv = Ag+ + e-
Next, the possible consequence of e-(aq) acting on a NO3- ion:
e-(aq) + NO3- = .NO3(2-) (unstable radical anion, created in a fast reaction, see Eq 26 at https://books.google.com/books?id=mckVFtJ7YecC&pg=PA30&a...)
.NO3(2-) + H2O = .NO2 + 2 OH- (see Eq 25, same source, but a very slow reaction)
Note, the nitrate ion (NO3-) is, by itself, not very light sensitive, but Silver metal and many of its salt are!
-------------------------------------------------
A related alternate path could be based on the presence of any Ag2O, where apparently Ag2O is capable of transforming into an efficient and stable
visible‐light photocatalyst (see https://onlinelibrary.wiley.com/doi/abs/10.1002/chem.2011010... ). Again the creation of electrons (and electron holes), may account for the NO2
product formation.
[Edited on 11-12-2018 by AJKOER]
|
|
|
Sulaiman
International Hazard
Posts: 3558
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Offline
|
|
So the time trusted equations;
3Ag + 4HNO3 (cold and diluted) = 3AgNO3 + 2H2O + NO
and
Ag + 2HNO3 (hot and concentrated) = AgNO3 + H2O + NO2
are probably correct ?
CAUTION : Hobby Chemist, not Professional or even Amateur
|
|
|
AJKOER
Radically Dubious
Posts: 3026
Registered: 7-5-2011
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by Sulaiman  | So the time trusted equations;
3Ag + 4HNO3 (cold and diluted) = 3AgNO3 + 2H2O + NO
and
Ag + 2HNO3 (hot and concentrated) = AgNO3 + H2O + NO2
are probably correct ? |
Good! And may be correct as well.
One issue is that the Ag is not in the same form as in my scenario, a very fine suspension, whereas your Silver is at its smallest, an Ag powder,
which if unreacted, could be easily separated off. Second issue, the 1st equation producing NO is most likely, but escaping NO does not immediately
convert to NO2 (like takes around a 100 seconds), which may preclude a quick smell check near the solution, but is in agreement with a smell
developing in a larger area (in your favor)!
As to the details of the prep, only Nimgoldman may know for sure.
-------------------------------
I would also now put on the table the possibility of a metal impurity (like Pb) including a sulfide presence (leading to H2S as suggested also by Herr
Haber).
[Edited on 11-12-2018 by AJKOER]
|
|
|
fusso
International Hazard
Posts: 1922
Registered: 23-6-2017
Location: 4 ∥ universes ahead of you
Member Is Offline
|
|
| Quote: Originally posted by Sulaiman | So the time trusted equations;
3Ag + 4HNO3 (cold and diluted) = 3AgNO3 + 2H2O + NO
and
Ag + 2HNO3 (hot and concentrated) = AgNO3 + H2O + NO2
are probably correct ? |
I've seen both, but never "cold+conc" nor "hot+dil". Is the rxn stoichiometry and NOx
byproduct actually dependent on conc or temp?
|
|
|
Tsjerk
International Hazard
Posts: 3022
Registered: 20-4-2005
Location: Netherlands
Member Is Offline
Mood: Mood
|
|
as far as I know, it does not depend on temperature, but these reactions do depend on concentration and follow the reaction schemes as shown by
Sulaiman.
|
|
|
fusso
International Hazard
Posts: 1922
Registered: 23-6-2017
Location: 4 ∥ universes ahead of you
Member Is Offline
|
|
| Quote: Originally posted by Tsjerk | | as far as I know, it does not depend on temperature, but these reactions do depend on concentration and follow the reaction schemes as shown by
Sulaiman. |
So textbooks that added the temperatures (hot/cold) as rxn conditions are misleading right?
|
|
|
AJKOER
Radically Dubious
Posts: 3026
Registered: 7-5-2011
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by Sulaiman | So the time trusted equations;
3Ag + 4HNO3 (cold and diluted) = 3AgNO3 + 2H2O + NO
and
Ag + 2HNO3 (hot and concentrated) = AgNO3 + H2O + NO2
are probably correct ? |
Here is my radical path analysis (after all, both •NO and •NO2 are radicals!):
Ag --> Ag+ + e-
2 HNO3 = 2 H+ + 2 NO3-
H+ + e- = •H (see Eq (6) at https://books.google.com/books?id=mckVFtJ7YecC&pg=PA6&am... )
Ag+ + NO3- = AgNO3
NO3- + •H = OH- + •NO2 (as •H = H+ + e-, more precisely may proceed via e- + NO3- = •NO3(2-) a fast reaction, see Eq 26 at https://books.google.com/books?id=mckVFtJ7YecC&pg=PA30&a... followed by the addition of H+ and slow breakdown of an intermediate to OH- +
•NO2 ; complexity confirmation, Eq 27 citing only 'Products')
Net: Ag + 2 HNO3 --> AgNO3 + H2O + •NO2
which seemingly confirms the hot and concentrated scenario. I say seemingly, as the plausible intermediate compound (I cited above) could have a minor
decomposition pathway (like to •OH + NO2-), which would imply that the net equation's stoichiometric coefficients above may just be approximately
accurate (sorry Sulaiman, 'time trusted equations' perhaps, and note, at least I did not pursue a rigorous following of Eq 27 and declare the entire
net reaction creates but 'Products'!).
-------------------------------------------------------------------------------
Now, for different conditions with NO only formation, I first scale by a factor of two:
2 Ag + 4 HNO3 --> 2 AgNO3 + 2 H2O + 2 •NO2
•NO2 + •NO2 = N2O4 (see Eq 21, reference below)
N2O4 + H2O = HNO2 + HNO3 (reaction not rapid and likely temperature sensitive, see Eq 23 at https://books.google.com/books?id=mckVFtJ7YecC&pg=PA30&a... )
Assuming the decomposition of Nitrous acid proceeds by:
3 HNO2 = HNO3 + 2 NO + H2O (Per Wikipedia, in “warm or concentrated solutions of HNO2”, link: https://en.wikipedia.org/wiki/Nitrous_acid )
Rescaling: HNO2 = 1/3 HNO3 + 2/3 NO + 1/3 H2O
Implied Net: 2 Ag + 8/3 HNO3 --> 2 AgNO3 + 2/3 NO + 4/3 H2O
Rescaling: 6 Ag + 8 HNO3 --> 6 AgNO3 + 2 NO + 4 H2O
Rescaling: 3 Ag + 4 HNO3 --> 3 AgNO3 + NO + 2 H2O
Which actually also agrees with:
“3Ag + 4HNO3 (cold and diluted) = 3AgNO3 + 2H2O + NO”
except for the “cold and dilute” HNO3 does not seem to apply to “warm or concentrated solutions” of HNO2 (?).
--------------------------------------------------------
Here are comments from a more recent 2006 article:
"The reaction between silver and nitric acid is of electrochemical nature. Because of considerable conductivity of the metallic layer, there is no
resistance to charge transfer through the solid region. The only remaining resistance is thus related to the NO3- and Ag+ ion transfer through the
aqueous electrolyte that fills the porous region of the solid phase. This resistance is considered by the inter-diffusion coefficient De in the
present system."
Also:
"...further measurements (Fig.2). The extraction rate decreases, for example, by increasing of the size of the particles dissolving in the nitric acid
solution as shown in Fig.2. This result is in obvious contradiction with chemical reaction mechanism reported by previous authors[6]."
Source: S.K. Sadrnezhaad, et al, 'Kinetics of Silver Dissolution in Nitric Acid from Ag-Au0.04-Cu0.10 and Ag-Cu0.23 Scraps', in J. Mater. Sci.
Technol., Vol.22 No.5, 2006. Link to download free pdf at https://www.researchgate.net/publication/259560528_Kinetics_...
So apparently, not a 'time trusted' chemical reaction either!
---------------------------------------------------------
[EDIT] Just found a source article: 'Temperature Dependence of Hydrogen Atom Reaction with Nitrate and Nitrite Species in Aqueous Solution' by Stephen
P. Mezyk
Research Chemistry Branch, AECLWhiteshell Laboratories, published in J. Phys. Chem. A, 1997, 101 (35), pp 6233–6237, DOI: 10.1021/jp970934i. Link:
https://pubs.acs.org/doi/abs/10.1021/jp970934i .
To quote from the abstract:
"Arrhenius parameters for the reaction of hydrogen atoms with NO3-, HNO2, and NO2- in aqueous solution have been determined by the use of pulse
radiolysis and electron paramagnetic resonance free induction decay attenuation measurements. At 25.0 °C, the calculated rate constants for these
compounds are (5.61 ± 0.51) × 10^6, .....
Computer modeling of these systems suggests that ·H atom reaction with either anion directly produces hydroxide anion and the corresponding NOx
radical."
So this 1997 source (which is several years after the book referenced above) provides a confirmation of my claimed slow reaction with no mention of a
minor path, however, did cite a temperature dependency.
[Edited on 13-12-2018 by AJKOER]
[Edited on 14-12-2018 by AJKOER]
|
|
|
Metallus
Hazard to Others
Posts: 116
Registered: 16-5-2013
Member Is Offline
Mood: No Mood
|
|
The yellow stain could very well be leftover HNO3 decomposing and giving off NO2.
The rotten smell is indeed unusual for both NOx and potential HCl. HCl has a faintly bleach smell but more penetrating and pungent but definitely not
putrid. NOx smells like car exhaust/smog.
The only known rotten smell is associated to sulphur compounds. How was your starting silver powder? Was it dark grey/black? Silver has a strong
affinity for H2S and gets covered in Ag2S with time. Perhaps you obtained some sulphur byproducts:
Ag2S + 4HNO3 --Z 2AgNO3 + 2NO + S + 2H2O
This could in turn further react in the strongly acidic/oxidizing environment and give off SOx. Did you not smell anything beside NOx during your
synthesis?
|
|
|
clearly_not_atara
International Hazard
Posts: 2692
Registered: 3-11-2013
Member Is Offline
Mood: Big
|
|
| Quote: Originally posted by Tsjerk | | as far as I know, it does not depend on temperature, but these reactions do depend on concentration and follow the reaction schemes as shown by
Sulaiman. |
I would guess temperature matters; at higher temperature, NO2 boils away more quickly, but at lower temperatures, it remains in solution and oxidizes
Ag while being reduced to NO. It can also disproportionate in aqueous solution:
3 NO2 + H2O >> 2 HNO3 + NO
A more complete explanation would be that both NO2 and NO are always produced -- they interconvert! -- but hotter/more concentrated shifts the
products towards NO2 while colder/more dilute favors NO.
[Edited on 04-20-1969 by clearly_not_atara]
|
|
|
AJKOER
Radically Dubious
Posts: 3026
Registered: 7-5-2011
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by Tsjerk | | as far as I know, it does not depend on temperature, but these reactions do depend on concentration and follow the reaction schemes as shown by
Sulaiman. |
| Quote: Originally posted by AJKOER |
.......
Here are comments from a more recent 2006 article:
"The reaction between silver and nitric acid is of electrochemical nature. Because of considerable conductivity of the metallic layer, there is no
resistance to charge transfer through the solid region. The only remaining resistance is thus related to the NO3- and Ag+ ion transfer through the
aqueous electrolyte that fills the porous region of the solid phase. This resistance is considered by the inter-diffusion coefficient De in the
present system."
Also:
"...further measurements (Fig.2). The extraction rate decreases, for example, by increasing of the size of the particles dissolving in the nitric acid
solution as shown in Fig.2. This result is in obvious contradiction with chemical reaction mechanism reported by previous authors[6]."
Source: S.K. Sadrnezhaad, et al, 'Kinetics of Silver Dissolution in Nitric Acid from Ag-Au0.04-Cu0.10 and Ag-Cu0.23 Scraps', in J. Mater. Sci.
Technol., Vol.22 No.5, 2006. Link to download free pdf at https://www.researchgate.net/publication/259560528_Kinetics_...
....................................................
Just found a source article: 'Temperature Dependence of Hydrogen Atom Reaction with Nitrate and Nitrite Species in Aqueous Solution' by Stephen P.
Mezyk
Research Chemistry Branch, AECLWhiteshell Laboratories, published in J. Phys. Chem. A, 1997, 101 (35), pp 6233–6237, DOI: 10.1021/jp970934i. Link:
https://pubs.acs.org/doi/abs/10.1021/jp970934i .
[Edited on 14-12-2018 by AJKOER] |
Also, per a related another work (‘Kinetic Characteristics of Silver Dissolution in Nitric Acid Solutions in the Presence of Ammonium Nitrate’ by
A. B. LEBE, D. YU. SKOPIN a nd G. I. MALTSEV, in Chemistry for Sustainable Development 20 (2012) p. 391-396), link: http://www.sibran.ru/upload/iblock/6b1/6b1d39caf4be374dc4a01... ) to quote:
“Studying the effect of the silver disk area demonstrated that the dissolution rate of the metal in nitric acid solutions is not dependent on the
presence of ammonium nitrate in the system, whereas it is proportional to the area of the working surface (S) being in contact with the solution.”
Assuming the electrochemical nature of the reaction, to be correct, means that the dissolution rate of the Silver metal is NOT a function of the
concentration of Silver relative to HNO3 (as long as there is some Ag presence, but the surface area of the silver (see comment by Lebe relating to
working area solution contact), along with the relative surface area in the presence of other metals, I would add as factors, note also, a particle
size comment above by Sadrnezhaad).
Also, the composition of the product mix, per my analysis, suggests a HNO3 concentration dependence (as is well known), and the article by Mezyk cites
a temperature effect (which is also true for electrochemical reactions). The effect of starting concentration of HNO3 is also depicted in Figure 2,
Graph (b) by Lebe.
I do support Sulaiman's stoichiometric coefficients, at least in the long term, for the action of HNO3 on Silver metal, but in the short-term,
especially for the case of dilute nitric acid, I would not be surprised if they are observational disagreements on the volume of NO gas evolution.
As the precise characterization of this reaction has been wrong for so long, I would be surprised if there is an agreement with my comments.
[Edited on 15-12-2018 by AJKOER]
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
