can water vapor (a gas) contain any dissolved material such as
chlorides or sulfates?

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Request for Question Clarification by pafalafa-ga on 02 May 2004 17:43 PDT

There's a lot of chemistry going on in the atmosphere, so much so that
it seems unlikely you'd actually be able to find pure water vapor --
that is, water vapor that was H2O and nothing else.  As soon as water
vapor appears in the atmosphere, it most likely starts interacting
with sulfates, nitrates, chlorine ions, and a whole bunch of other
stuff.

So, the answer to your question seems to be "Yes, it certainly can"
(unless you're no longer willing to call it water vapor, since it
contains things other than pure water -- that's more of a semantic
issue than one of chemistry).

However, I imagine you're looking for more detailed information than
just a simple "Yes".  So...what more do you need?

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Clarification of Question by kenbondy-ga on 02 May 2004 18:32 PDT

Ok let's say it this way.  Assume a volume of water containing heavy
concentrations of dissolved water soluble chlorides or sulfates.  As
this water evaporates, does the instant vapor contain any chloride or
sulfate ions.  I am not interested in any future interactions between
chemicals in the atmosphere, just whether or not the vapor, as it
evaporates, takes any of the dissolved ions with it.

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Request for Question Clarification by pafalafa-ga on 02 May 2004 19:49 PDT

In general, no.  As the water evaporates, it starts out as pretty pure
water vapor, and leaves behind any dissolved compounds in the
remaining liquid.

This is why, as more and more water evaporates from a body of water
(it can be a lake, or a pot of water on your stove), you wind up with
increasing mineral concentrations in the remaining water left behind. 
These depostis can show up as a visible mineral deposit, or a salty
taste in the water, etc.

If I remembered more of the actual chemistry and physics, I would post
an answer.  I'll probably have to leave it for another researcher to
explain the details, however, unless I can dig out some of my old
textbooks and refresh some distant memories.

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Request for Question Clarification by pafalafa-ga on 02 May 2004 19:51 PDT

P.S.  This is also the reason why -- if someone wants pretty pure
water -- they distill it, because the process of turning the liquid
water into vapor is one of the best purification steps possible.

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Clarification of Question by kenbondy-ga on 02 May 2004 20:33 PDT

pafala-ga
That pretty much answers my question.  The only other thing that would
be VERY useful to me is a published reference (textbook, article,
etc.) that says the same thing you did.  Thanks,
    ++Ken++

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Request for Question Clarification by livioflores-ga on 03 May 2004 00:20 PDT

Hi kenbondy!!

I agree with pafalafa 99.9%!!
When the water is boiling turbulences from steam and from the mass of
water makes that droplets of unvaporized liquid be carried by the
steam, so if you can see with a magnifier the steam cloud you will
"see" mixed with the water molecules very small droplets of solution,
this is why 99.9% pure water can be obtained by distillation, not
100%. The same could happen if the solute is a liquid with a similar
(or very close) boiling point than the water.
For example, this is why, for some special purposes, tri-distilled
water is needed (99.999% pure water).

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Request for Question Clarification by pafalafa-ga on 17 May 2004 07:05 PDT

kenbondy-ga,

Sorry to have taken so long with a reply of some sort.  I've been a
bit sidetracked by -- among other things -- a massive swarm of
cicadas!

First, I want to clarify an earlier remark.  With some further
investigation, it became clear that the term "distillation" is
generally used to refer to separating one liquid from another, for
example, alcohol in water.  So it's not quite the right term for your
situation, where you asked about separating dissolved chlorides etc
(generally referred to as "salts") from water -- the correct term here
is "evaporation".

A simple presentation and citation of evaporation is this BBC educational website:

http://www.bbc.co.uk/schools/gcsebitesize/chemistry/structure/separationtechniquesrev3.shtml

If you click on the "Next" button, you'll find a similar page for "Distillation".

Is this what you need?  Or are you looking for something more technical in nature?

Let me know.

pafalafa-ga

Despite what others have said, the *general* answer to your question
is "yes" - the gas phase in equilibrium with an aqueous solution *can*
contain appreciable quantities of components other than H2O.  The key
parameter here is the vapor pressures of the various components making
up the solution, and how those vapor pressures vary as the composition
of the solution, temperature, and total pressure vary.  Evaporation
(or distillation) of an aqueous solution does not always result in a
gas (vapor) phase that is richer in water than the starting solution. 
Consider, for example a solution made up of ethanol (grain alcohol)
and water.  The gas phase (vapor) for any mixture of these two
compounds containing less than 95.5% of ethanol by weight will contain
*more* ethanol vapor than water vapor.  If this were not so, then one
couldn't make high-proof alcoholic beverages by distillation.

The vapor pressure of compounds that are solids at the temperature of
interest are usually quite low, and hence compounds like NaCl or CaSO4
will have very, very low concentrations in a gas phase in equilibrium
with an aqueous solution at the temperatures and pressures one
typically encounters on the surface of the Earth.  Nevertheless, the
gas phase in equilibrium with a solution of NaCl *will* contain trace
amounts of NaCl vapor, and potentially larger quantities of of more
volatile chloride-containing species, such as HCl.  (In the case of
HCl, its concentration in the vapor phase will depend strongly on the
pH of the solution.)  Concentrations of chloride exceeding 100 parts
per million have been measured in the steam associated with geothermal
systems, and this can cause severe corrosion problems in the
"plumbing" systems at geothermal power plants, so your question is of
more than academic interest!

Despite of what hfshaw-ga said

strict answer is no.

You may have a mixture of gases, but there is no such thing
as 'gas dissolved in another gas'.

The word 'dissolved' applies to a solution - meaning liquid phase.

Hedgie-ga>>  ...the strict answer is no.
Hedgie-ga>>  You may have a mixture of gases, but there 
Hedgie-ga>>  is no such thing as 'gas dissolved in another gas'.
Hedgie-ga>>  The word 'dissolved' applies to a solution 
Hedgie-ga>>  - meaning liquid phase.

Hedgie-ga is incorrect.  The most general chemical definition of a
"solution" is a homogenous (single phase) mixture of one or more
substances that are uniformly dispersed at the molecular scale.

For instance, the classic thermodynamics text, "Thermodynamics", by
Lewis, Randall, Pitzer, and Brewer (1961, McGraw Hill) has this to say
about solutions (p. 8): "Any homogeneous system, whether solid,
liquid, or gaseous, is called a solution if its composition is
variable.  Thus, air, brine, glass, and a mixed crystal of alum and
chrome alum are all called solutions.  The components [of the
solution] are the substances of fixed composition which can be mixed
in varying amounts to form the solution."

It is common for people to think of solutions as being restricted to
the liquid phase, but this is an unnecessary restriction, and one that
limits ones thinking.  I am a geochemist, even other chemists are
sometimes surprised when I talk about minerals being "solid solutions"
(a term that is very commonly used by mineralogists and material
scientists, but not often encountered in wet chemistry.  Lewis et
al.'s example of the alum/chrome alum crystal would be called a solid
solution.).

RE  hfshaw-ga on 06 May 2004 10:49 PDT

I would agree that term solution should apply to any condensed phase,
solid or liquid but I would not apply it to gas phase.

It is  a matter of definition. I prefer more
narrow definition: in mixture (of gases) the molecules of components
are (in certain sense) independent (as indicated by Dalton's law), in
solutions, there is a solvent and solute and stronger interaction
between the two.

What the statistical distribution of preferences would be I do not know,
but I guess  that most physicists would be lean to the more narow definion....

RE: hedgie-ga 

Actually, I think the argument for including gases in a definition for
solutions is even stronger than for including solids -- crystalline
solids, anyway.

Consider that both liquids and gases are both fluids, and that the
distinction between them evaporates (pun intended) above the critical
point.  Note that it is possible to move from a gaseous state to a
liquid state in a continuous fashion (i.e., with no discontinuous
changes in physical or thermodynamic properties -- no phase changes of
any order), simply by changing the temperature and pressure along a
P-T path that travels above the critical point.

Would a single-phase, multicomponent, supercritical fluid be called a
"solution" in your definition of the term?

hfshaw-ga

   I yield. 
I was connecting the word 'solution' with the process of 
    solvation 
as described here -- http://www.fact-index.com/s/so/solvation.html

So criterion would be specific interaction between the molecules 
-- one would have scale of 

 (ideal gas) - no interaction - mixture
 (physical forces) - solution 
 (chemical bond) - new compound 

BUT, looking at the dictionary 
 http://dictionary.reference.com/search?q=solution
 http://dictionary.reference.com/search?q=mixture

I will accept (in interest of simplicity and uniformity)

that solution is

 A homogeneous mixture of two or more substances, which may be solids,
liquids, gases, or a combination of these.

Based on that, I am withdrawing my previous comment.

hedgie

This is a very easy question to answer. If the solutes (e.g.,
chlorides, sulfates) have a vapor pressure and boiling point less than
or equal to that of water, then they can also evaporate at the same
temp that the water is at. It really doesn't matter that the water is
involved, although whenever two solutions or a solvent and a solute
are mixed together, they will slow each other from evaporating-- i.e.,
solutions have higher boiling points than just the pure solvents
alone.