aeacfm
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NaOH dissolution fumes
every time i dissolute NaOH (but in high concentrations) some fumes generated which make me cant breath !!
what are these fumes
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Jor
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These are small droplets of water containing dissolved NaOH.
Boiling solutions (but also if the aqueous solution is close to the boiling point) release very small droplets, aerosols, in some salts may be
dissolved, in this case NaOH. This is the irritating smell you notice. This is not a really a problem, but don't breath it too much.
This is exactly the reason why I never boil down solutions containing mercury or lead, because this contaminates the area with small amounts of the
metal-salts.
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woelen
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Jor's answer is right, but there is more to this. Why do you get NaOH in the droplets? The solution is far from boiling, but still NaOH is in the
fumes from the solution, while this is an ionic compound.
On the other hand, if I boil a mix of water and sulphuric acid with e.g. 30% H2SO4 then the boiling liquid does not contain a noticeable amount of
H2SO4. Even when a dilute solution of a volatile compound like HBr is distilled then initially only water comes over.
The formation of aerosols with mercury or lead can easily be explained, because of the boiling of the liquid, small droplets are ejected into the air.
This is just a mechanical phenomenon. But as long as no bubbles are produced, then no lead or mercury will be present in the mist from the solution.
An interesting experiment would be to take a little piece of paper, soaked with Na2S and keep this above a hot solution of Pb(NO3)2 or HgCl2. I expect
that as long as the liquid is not boiling, the paper will not become dark.
On the other hand, if you take a piece of humid pH paper and keep that above a warm solution of NaOH do you think that the paper will display a color
for high pH?
One thing which I can imagine is due to the choking fumes on dissolving of solid NaOH is that very small bubbles are produced in the solution (e.g.
dissolved air which is driven out, or small amounts of air, trapped in the granules of NaOH) which slowly move to the surface and cause formation of
an aerosol.
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Sedit
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"But as long as no bubbles are produced, then no lead or mercury will be present in the mist from the solution."
Sorry woelen this isn't true and you can repeat my experiment to prove me wrong if you like.
I was evaporating a solution of HgCl2 and in order to eliminate the possibility of partical release like we are talking about here I used a double
boiler type setup with warm water in the lower section. This water isn't even hot enough to burn ones finger but still warm enough to slowly evaporate
water. I placed a piece of glass over it just to check and low and behold when the condensation evaporated I was disturbed to see HgCl2 crystals had
formed on the glass meaning no matter how hard you try the Hg slowly gets out.
. I haven't messed with Hg salts since because im positive i can not avoid contamination.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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DJF90
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HgCl2 sublimes, as such it was known in the old days as "corrosive sublimate"... probably not a "model compound" to test this theory with.
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Sedit
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But is the vapor pressure of HgCl2 close enough to that of waters that they should "sublime" together so to speak? The solution was not really
saturated or anything so I would expect the water to come over before it started to sublime.
Iv been considering testing this even further on a hot summer day by placing a piece of glass over the solution and see if even the very slight heat
from the sun is enough to carry it along with the water vapors.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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MagicJigPipe
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If this were true distillation of water would not work and would still contain significant amounts of dissolved solids. Of course a molecule might
stray from the solution every now and then but surely not enough to be significant. I'm pretty sure I have held pH paper above hot NaOH soln. and I
remember somewhat distinctly that it did not show increased pH.
If HgCl2 is subject to sublimation it will do so at any temperature (depending on pressure) but just to a lesser extent, right? In the same way that
water evaporates even at 0*C just relatively slowly. In this sense won't many if not most ionic salts "sublimate" just at a rate that renders the
sublimation insignificant? I keep asking questions like this about things that happen but are not considered significant and are therefore, for
practical purposes, ignored but no one will answer me. Seriously, what's going on?
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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Sedit
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I was under the impression that as a substance evaporated, especially in a closed system, it exerts a pressure with the force of the vapor pressure of
that substance so that as two substances where in the same system the ones sublimination point so to speak could not be reached or atlest seriously
reduced until the substance exerting the higher vapor pressure was eliminated in one way or another(evaporation ect...) It just seemed like simple
logical conclusion to me so I never gave it much thought to be honest until I seen the HgCl2 come out of water regardless of the temperature used.
Surely the gurus around here could clear this up for us laymen once and for all....right?
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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MagicJigPipe
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The key words here are "seriously reduced". The HgCl2 vapor is there, but in what concentration?
I think I remember Raoult's law(?) from Gen. Chem. 2. Now I will attempt to relearn it and apply it. Maybe it will tell us something about this
problem (Sedit)?
According to an MSDS the vapor pressure of HgCl2 is:
1 @ 136.2C
But of course we can't use this because, in solution, it is split into Hg2+ and Cl- ions surrounding by water molecules.
But let's see. Sat. soln. would be 7.4 g per 100 mL. That's about a mole fraction of .005 which is just multiplied by less than 1 mmHg so this can
obviously not be used to explain.
I'm thinking there must be some bubbling or splashing that you didn't notice. How long was the soln. heated?
Oh, well, see below for your answer. It is volatile, even at 100*C. Even with the water in the system this should still allow for the vapors to
visibly condense over time.
[Edited on 11-12-2010 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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Lambda-Eyde
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Quote: Originally posted by MagicJigPipe  |
If HgCl2 is subject to sublimation it will do so at any temperature (depending on pressure) but just to a lesser extent, right? In the same way that
water evaporates even at 0*C just relatively slowly. In this sense won't many if not most ionic salts "sublimate" just at a rate that renders the
sublimation insignificant? I keep asking questions like this about things that happen but are not considered significant and are therefore, for
practical purposes, ignored but no one will answer me. Seriously, what's going on? |
I'm not following the discussion at all, but I just want to add that HgCl<sub>2</sub> is a molecular compound, not ionic. Which may help
in explaining its odd behavior with regards to sublimation.
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entropy51
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The Merch Index says HgCl2 volatilizes at 300 C. Also that it is "slightly volatile at ordinary temperatures, appreciably so at 100 C".
Based on this, I would guess that if you heated it a bit, some might volatilize onto a cooled surface in close proximity. I have to agree with DJF90.
Sounds like an interesting quantitative experiment for someone with some HgCl2 and a good balance. Blogfast25??
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Sedit
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I got some HgCl2 that I wish to not touch with a ten foot pole and some HgSO4 as well. Either way the best scale I have goes to .1 grams which I dont
feel is enough to perform an experiment of this nature.
Not to mention im a messy basterd.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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Magpie
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In one of my books there is a small graph of the vapor/liquid equilibrium composition vs temperature for the system NaOH-H2O. Along with it the text
says "Note that a discernible concentration of sodium hydroxide in the vapor phase is not obtained until the liquid phase reaches 95 per cent NaOH and
boils at some 700F (371C)." This is rather what I would expect for an inorganic ionic dissolved substance that has a mp of 318C and a bp of 1390C.
But what is meant by "discernible." This may depend on the substance and the sensitivity of the method used for measurement, ie, a titration, a
conductivity meter, damp pH paper, the human nose, etc.
Many solids, eg, some metals, can be smelled at room temperature. All solids have some vapor pressure.
The single most important condition for a successful synthesis is good mixing - Nicodem
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blogfast25
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I've often asked myself the same question when dissolving metals in acids: there too a characteristic smell can usually be observed, especially for
metals that are easily oxidisable by H3O+ alone and lots of hydrogen evolves. A muff, metalicky odour, not very pleasant. With Al and Fe it's
particularly similar, in my perception...
[Edited on 12-11-2010 by blogfast25]
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DJF90
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I've noticed this with magnesium and zinc, although I began to wonder if it was metal particulates I could smell, or whether it was nascent hydrogen
(pretty unlikely me thinks?)...
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blogfast25
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Certainly hydrogen (H2) is odourless and nascent hyfrogen (H. radicals) is very shortlived. Metal particles? Unless extremely fine they can't tickle
your olfactory system, you need some vapour pressure for that, as far as I know...
I had been thinking perhaps silane or other volatile metallo hydrides (from trace alloy elements e.g.) but many are highly inflammable/unstable in the
presence of oxygen...
Tin metal with hydrochloric acid also smells peculiarly...
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ScienceSquirrel
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I have made iron salts by dissolving steel wool in sulphuric acid.
The gas that comes off is mainly hydrogen but it has a little hydrogen sulphide and maybe something more.
I doubt that a trace of arsine would inflame and it would give the gas a slightly garlicky odour.
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blogfast25
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Maybe trace elements hydrides are causing it, it sounds plausible.
I've just taken receipt of 50 g of fairly pure tin (99.9 %), so I'll see how that whiffs with strong HCl... Where I wrote 'tin' previously I meant
pewter of course (about 95 % Sn)...
[Edited on 12-11-2010 by blogfast25]
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12AX7
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Theory:
Suppose the NaOH grains are porous. This seems reasonable, as NaOH is generally produced in prill form, and the water removed during crystallization
will leave pores.
When prills are added to water, the outer surface is completely wetted and begins to dissolve. However, water is not able to penetrate the grain
completely, and air bubbles become trapped inside.
As the prill dissolves, air bubbles are loosened. The bubbles are very small, corresponding to the prill's pore size.
When these bubbles reach the surface of the solution, they burst, releasing very fine particles of NaOH solution. This aerosol irritates the mucosa,
leading to a burning sensation when inhaled.
The action of very fine bubbles bursting seems to be different from the bursting of large bubbles, which result in correspondingly large droplets,
which are not able to form an aerosol.
If the fine bubbles are not produced by this mechanism, perhaps there is a chemical explanation. This seems unlikely, as the only gas that could be
produced is ammonia, which has an odor. CO2, from hard water for instance, would be bound instead. Hydrogen or oxygen would require redox
conditions, which are absent.
Tim
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blogfast25
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I've often thought that very localised overheating (from solvation energy) could contribute to fine bubble formation...
One way to test Tim's theory would be to dissolve fused NaOH...
[Edited on 12-11-2010 by blogfast25]
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woelen
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With the HgCl2 I indeed must say I am wrong. This is not an ionic compound in aqueous solution and then it is sufficiently volatile to get out of
aqueous solution even below the boiling point of water. This, however, is not the case with e.g. Hg2(NO3)2 or with Pb(NO3)2 and certainly not with
NaOH (that's what the topic started with).
So, I indeed think that Tim's theory may be a good description of what happens.
An easy check is to take some NaOH, dissolve this in water (which gives a choking fume). Then wait for a few hours such that the liquid is completely
clear and has cooled down. Then heat this liquid again but do not allow it to boil (e.g. let it heat up to 80 C or so) and carefully waft some fume
from this liquid to your nose.
Maybe I'll try this little experiment tomorrow afternoon.
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12AX7
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| Quote: Originally posted by blogfast25 | I've often thought that very localised overheating (from solvation energy) could contribute to fine bubble formation...
One way to test Tim's theory would be to dissolve fused NaOH...
[Edited on 12-11-2010 by blogfast25] |
The trouble with any other kind of gas formation, as I noted, is it's either reactive, or doesn't belong. If overheating caused localized boiling, it
could release dissolved gasses, mostly CO2 and O2, of which only O2 could survive in this solution. But the very fine bubbles would also redissolve
easily, since we're talking transient formation here.
On the other hand, as temperature rises, gas solubility drops. So it could be a contributing factor.
Easy test: use preboiled water and fused NaOH.
Keep in mind that NaOH contains nucleation sites. Merely reheating the solution may not induce bubble formation. Fused NaOH may not nucleate as
well, either.
Tim
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aeacfm
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| Quote: Originally posted by 12AX7 | Theory:
Suppose the NaOH grains are porous. This seems reasonable, as NaOH is generally produced in prill form, and the water removed during crystallization
will leave pores.
When prills are added to water, the outer surface is completely wetted and begins to dissolve. However, water is not able to penetrate the grain
completely, and air bubbles become trapped inside.
As the prill dissolves, air bubbles are loosened. The bubbles are very small, corresponding to the prill's pore size.
When these bubbles reach the surface of the solution, they burst, releasing very fine particles of NaOH solution. This aerosol irritates the mucosa,
leading to a burning sensation when inhaled.
The action of very fine bubbles bursting seems to be different from the bursting of large bubbles, which result in correspondingly large droplets,
which are not able to form an aerosol.
If the fine bubbles are not produced by this mechanism, perhaps there is a chemical explanation. This seems unlikely, as the only gas that could be
produced is ammonia, which has an odor. CO2, from hard water for instance, would be bound instead. Hydrogen or oxygen would require redox
conditions, which are absent.
Tim |
good explanation
but you said i the chemical explanation that" the only gases could be produced is amonia" , ans i am asking what amonia here in NaoH solution or you
mean other case????
other thing together with these fumes the temperature pf the solution becomes very high (with out heating or boiling i am working at room temperature
) may due to the heat of fromation or hydration but no external heat applied to the system
any way good shot sir
[Edited on 13-11-2010 by aeacfm]
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