Questions on salt water vs fresh water....


by jim
Tags: fresh, salt, water
jim
#1
Nov23-07, 05:01 AM
P: n/a
I live in an area that is experiencing a long drought. So, I got to
thinking about the differences in fresh and salt water and have a few
questions that I'd like your thoughts on.

Just what happens to salt in salt water?

Do the molecules of water and salt combine or is the salt simply
suspended in the water?

If it is just suspended, what makes it stay suspended?

Why doesn't it settle to the bottom of the container?

Are the water molecules heavier than the salt molecules or vice versa or
are they approximately the same weight?

Thanks for any light that you could shine on these questions!

jim

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PhY
PhY is offline
#2
Nov23-07, 07:33 AM
P: 49
Quote {Just what happens to salt in salt water?}
Salt in the water is Dissolved.
To extract the salt you need to leave it in a Salt pan to dry.
If you dry the salty water you will have salt left.
mathman
mathman is offline
#3
Nov23-07, 06:35 PM
Sci Advisor
P: 5,939
Just what happens to salt in salt water?

Do the molecules of water and salt combine or is the salt simply
suspended in the water?
Salt in water is ionized into individual Na+ and Cl- ions, which mix freely with the water molecules.

Androcles
#4
Nov24-07, 05:00 AM
P: n/a

Questions on salt water vs fresh water....



"jim" <jim@home.net> wrote in message
news:wma1j.4013$F87.3448@bignews6.bellsouth.net...
:I live in an area that is experiencing a long drought. So, I got to
: thinking about the differences in fresh and salt water and have a few
: questions that I'd like your thoughts on.
:
: Just what happens to salt in salt water?

It dissolves.

: Do the molecules of water and salt combine or is the salt simply
: suspended in the water?

Sand is a suspension, salt is a solution.

Thoroughly mix salt and sand, add water, pour through a coffee filter.
Evaporate off the water and you've separated the salt and sand.
You can speed up the evaporation by boiling the water

: If it is just suspended, what makes it stay suspended?
else it is not.


: Why doesn't it settle to the bottom of the container?

Because it is a solution and not a suspension.

:
: Are the water molecules heavier than the salt molecules or vice versa or
: are they approximately the same weight?

Which is heavier, a ton of old iron or a ton of feathers?

: Thanks for any light that you could shine on these questions!
:
: jim
:

PhY
PhY is offline
#5
Nov24-07, 05:16 AM
P: 49
Quote Quote by Androcles View Post

:
: Are the water molecules heavier than the salt molecules or vice versa or
: are they approximately the same weight?

Which is heavier, a ton of old iron or a ton of feathers?

: Thanks for any light that you could shine on these questions!
:
: jim
:
He might have meant the mass of a single molecule of Salt vs a single H20.
Timo A. Nieminen
#6
Nov25-07, 05:31 AM
P: n/a
On Fri, 23 Nov 2007, jim wrote:

> Just what happens to salt in salt water? > > Do the molecules of water

and salt combine or is the salt simply > suspended in the water? > > If
it is just suspended, what makes it stay suspended? > > Why doesn't it
settle to the bottom of the container?

Why don't air molecules all settle to the ground? Not a trivial
question! The simple answer is that the air isn't cold enough - the
molecules are all moving around (the temperature tells you the average
kinetic energy of the molecules). If they're moving around, they can
hardly be lying on the ground. Stuff suspended in water behaves the
same.

Why do heavier things settle to the bottom? Their kinetic energy is the
same as that of lighter things. Since KE = 1/2 mv^2, that means that the
thermal motion of heavier things is much slower, and they can settle.

A fancier answer is that a dilute suspension in water obeys the ideal
gas law, just like a gas does.

> Are the water molecules heavier than the salt molecules or vice versa or
> are they approximately the same weight?


No salt molecules in solution, just Na and Cl ions. Water molecule is
H2O, so easy to look up on a periodic table. What's more important, the
weight or the density?

--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/...,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html

CWatters
#7
Nov25-07, 05:31 AM
P: n/a
"jim" <jim@home.net> wrote in message
news:wma1j.4013$F87.3448@bignews6.bellsouth.net...
> I live in an area that is experiencing a long drought. So, I got to
> thinking about the differences in fresh and salt water and have a few
> questions that I'd like your thoughts on.
>
> Just what happens to salt in salt water?
>
> Do the molecules of water and salt combine or is the salt simply
> suspended in the water?


They don't combine they mix. If they combined it would be a compound.

http://www.answers.com/topic/solution

> If it is just suspended, what makes it stay suspended?
> Why doesn't it settle to the bottom of the container?


The density is the same/similar.

> Are the water molecules heavier than the salt molecules or vice versa or
> are they approximately the same weight?


It's the density that matters not the weight.

> Thanks for any light that you could shine on these questions!
>
> jim
>


Herman Family
#8
Nov26-07, 05:00 AM
P: n/a

"jim" <jim@home.net> wrote in message
news:wma1j.4013$F87.3448@bignews6.bellsouth.net...
>I live in an area that is experiencing a long drought. So, I got to
> thinking about the differences in fresh and salt water and have a few
> questions that I'd like your thoughts on.
>
> Just what happens to salt in salt water?
>
> Do the molecules of water and salt combine or is the salt simply
> suspended in the water?
>
> If it is just suspended, what makes it stay suspended?
>
> Why doesn't it settle to the bottom of the container?
>
> Are the water molecules heavier than the salt molecules or vice versa or
> are they approximately the same weight?
>
> Thanks for any light that you could shine on these questions!
>
> jim
>


The salt you are most familiar with is sodium choride. The salt will
dissociate into sodium ions and chloride ions, each of which interact with
the water due to their ionic nature. This means that salt water really
isn't water with salt in it, it is water with the constituents of salt in
it. Once there is too high a concentration of sodium and chlorine in water,
they can precipitate out.

Sand, on the other hand, stays pretty much intact, so a mixture of sand and
water is just a bunch of sand particles in water. It doesn't interact
chemically to any great extent with the water. When you stop mixing the
sand/water suspension, the sand and water will separate (or at least the
sand will drop to the bottom). It will be wet sand.

Michael

jim
#9
Nov26-07, 05:00 AM
P: n/a

"CWatters" <colin.watters@turnersoak.plus.com> wrote in message
news:13ke21m14r2oc81@corp.supernews.com...
> "jim" <jim@home.net> wrote in message
> news:wma1j.4013$F87.3448@bignews6.bellsouth.net...
>> I live in an area that is experiencing a long drought. So, I got to
>> thinking about the differences in fresh and salt water and have a few
>> questions that I'd like your thoughts on.
>>
>> Just what happens to salt in salt water?
>>
>> Do the molecules of water and salt combine or is the salt simply
>> suspended in the water?

>
> They don't combine they mix. If they combined it would be a compound.
>
> http://www.answers.com/topic/solution
>
>> If it is just suspended, what makes it stay suspended?
>> Why doesn't it settle to the bottom of the container?

>
> The density is the same/similar.


Would you be referring to the mass or size of the individual molecules when
you refer to density?

Salt molecules seem much more densely packed when in a crystaline state
than those of water. And, to my untrained mind, it would seem that the
water molecules are more dense than the salt molecules dispersed throughout
them.

I know it is a childish question, but just when do you mean by density?

These things bring 2 more questions to mind...what is it about water that
makes salt crystals seperate from one another? Why do salt molecules form
crystals when the salt water evaporates instead of just a fine powder or
dust?

>
>> Are the water molecules heavier than the salt molecules or vice versa or
>> are they approximately the same weight?

>
> It's the density that matters not the weight.


By density, do you mean the mass or size of the molecule?

I am aware of filters used to filter salts out of salt water. I assume that
this works because the H2O molecules are smaller in size than the salt
molecules. But, it would seem, that not all salt water solutions are equal.

For instance, I saw a re-run of a show last night on cable (Deep Planet)
that showed something that may play into my questions. The scientists were
in a specially built submersible taking pictures and film for this speacial
of the ocean floor at great depths (10,000 feet or so). At one point, they
came across a "pond" in the ocean. It was an actual "pond" with a shore and
water within it that was of a much greater density than the water that they
were already in. The film maker said that when they tried to enter the
"pond", the submersible simply "bounced off" of it. The wanter in the
undersea "pond" was too dense to be penetrated by the submersible. In fact,
he said that thier attempt to enter the sea-pond created "waves" across its
surface that rippled out to it shores.

He also refered to this sub-sea pond's water as "brine". Seeing as how they
are already in the sea (a brine solution) how would this "pond" be filled
with more dense salt water than the water that it itself was in? Shouldn't
it reach equilibrium with the surrounding sea water through natural means?

A pond under the sea. Jus one more reason that I am not sure that we really
understand the nature of salt water at all, although we may understand some
of its properties.

Thanks for your help!

jim

N:dlzc D:aol T:com (dlzc)
#10
Nov27-07, 05:00 AM
P: n/a
Dear jim:

"jim" <jim@home.net> wrote in message
news:Orn2j.2754$k27.68@bignews2.bellsouth.net...
...
> Salt molecules seem much more densely packed when
> in a crystaline state than those of water. And, to my
> untrained mind, it would seem that the water molecules
> are more dense than the salt molecules dispersed
> throughout them.


No. The density of salt water is higher than the density of
fresh water.

...
> These things bring 2 more questions to mind...what is it
> about water that makes salt crystals seperate from one
> another?


The water molecule is polar, with a slight negative charge on one
side. The hydrogens don't bond diametrically opposite each other
on the oxygen. So the oxygen atom is attractive to the
positively charged sodium, and the hydrogen atoms are attractive
to the chloride.

> Why do salt molecules form crystals when the salt
> water evaporates instead of just a fine powder or dust?


Within its ability to move in the disappearing fluid, salt
crystals are at a slightly lower energy state, than would be
dispersed NaCl molecules.

David A. Smith

Tom Knight
#11
Nov27-07, 05:00 AM
P: n/a
"Timo A. Nieminen" <timo@physics.uq.edu.au> writes:
> Just what happens to salt in salt water?
> Do the molecules of water and salt combine or is the salt simply
> suspended in the water? If it is just suspended, what makes it stay
> suspended? Why doesn't it settle to the bottom of the container?


If you centrifuge salt solutions at high speed, a concentration
gradient indeed appears. Biologists use this with cesium chloride (a
particularly heavy ion) to set up a density gradient for separation of
biomolecules by density.

jim
#12
Nov27-07, 05:01 AM
P: n/a
"Herman Family" <the_sawdust_place_no_underscore@frontiernet.net> wrote in
message news:N5N1j.21249$B25.19492@news01.roc.ny...
>
> "jim" <jim@home.net> wrote in message
> news:wma1j.4013$F87.3448@bignews6.bellsouth.net...
>>I live in an area that is experiencing a long drought. So, I got to
>> thinking about the differences in fresh and salt water and have a few
>> questions that I'd like your thoughts on.
>>
>> Just what happens to salt in salt water?
>>
>> Do the molecules of water and salt combine or is the salt simply
>> suspended in the water?
>>
>> If it is just suspended, what makes it stay suspended?
>>
>> Why doesn't it settle to the bottom of the container?
>>
>> Are the water molecules heavier than the salt molecules or vice versa or
>> are they approximately the same weight?
>>
>> Thanks for any light that you could shine on these questions!
>>
>> jim
>>

>
> The salt you are most familiar with is sodium choride. The salt will
> dissociate into sodium ions and chloride ions, each of which interact with
> the water due to their ionic nature. This means that salt water really
> isn't water with salt in it, it is water with the constituents of salt in
> it. Once there is too high a concentration of sodium and chlorine in
> water,
> they can precipitate out.


So the sodium and chloride ions form bonds with the water molecules because
the attraction of the ions to H2O is stronger than their attraction to one
another, and when there are no more H2O "connections" available for more
sodium or chloride ions to attach themselves to the sodium and chloride ions
simply re-connect to each other via their weaker attraction and drift to the
bottom?

Did I get that right?

>
> Sand, on the other hand, stays pretty much intact, so a mixture of sand
> and
> water is just a bunch of sand particles in water. It doesn't interact
> chemically to any great extent with the water. When you stop mixing the
> sand/water suspension, the sand and water will separate (or at least the
> sand will drop to the bottom). It will be wet sand.


Got it. The sand doesn't break apart, it is just sand, no matter where in
the suspension it is located - but salt actually changes its molecular
makeup bt seperating into sodium and chloride in the presence of water that
has not already been saturated to its limit with salt.

Ok.....well, idea #1 won't work, but idea #2 still has some life in it.
I've got to purchase a few tools from a school supply company and start
playing "mad person" (if I were a scientist it would sound so much cooler).

Thanks for you help!

Richard Saam
#13
Nov27-07, 05:02 AM
P: n/a
N:dlzc D:aol T:com (dlzc) wrote:
> Dear jim:
>
>
>
> The water molecule is polar, with a slight negative charge on one
> side. The hydrogens don't bond diametrically opposite each other
> on the oxygen. So the oxygen atom is attractive to the
> positively charged sodium, and the hydrogen atoms are attractive
> to the chloride.
>
>
>>Why do salt molecules form crystals when the salt
>>water evaporates instead of just a fine powder or dust?

>

Extremely fast water evaporation will tend to form fine powder or dust.
It is a salt nucleation process from supersaturated ion solution.
Once nucleated crystals are formed, the ions from solution
will tend to go to already formed salt crystals.
but will tend to form many new crystals
if ions are in a supersaturated condition created by rapid water evaporation
making the energetics favorable for creating new additional crystals
rather than migrating to existing crystals.

Essentially, it takes more energy to form a sodium chloride crystal
from one sodium ion and one chloride ion
than attaching those same ions to an existing sodium ion crystal.

The effect is more pronounced in less water soluble crystals
such as calcium carbonate.

>
> Within its ability to move in the disappearing fluid, salt
> crystals are at a slightly lower energy state, than would be
> dispersed NaCl molecules.
>
> David A. Smith
>


Energy Concept in terms of free energy (kilo cal/g mole)
Sodium crystal -> sodium+ ion in water & chloride- ion in water

Free energy Free energy Free energy
Sodium crystal Sodium ion in water Chloride ion in water
-91.79 > -62.59 + -31.35

-91.79 > -93.94

More negative free energy indicates
a tendency for the reaction to go in that direction.

Stumm and Morgan
Aquatic Chemistry
goes into this type of thing in detail

Richard

Richard Saam
#14
Nov27-07, 05:02 AM
P: n/a
N:dlzc D:aol T:com (dlzc) wrote:
> Dear jim:
>
>
>
> The water molecule is polar, with a slight negative charge on one
> side. The hydrogens don't bond diametrically opposite each other
> on the oxygen. So the oxygen atom is attractive to the
> positively charged sodium, and the hydrogen atoms are attractive
> to the chloride.
>
>
>>Why do salt molecules form crystals when the salt
>>water evaporates instead of just a fine powder or dust?

>

Extremely fast water evaporation will tend to form fine powder or dust.
It is a salt nucleation process from supersaturated ion solution.
Once nucleated crystals are formed, the ions from solution
will tend to go to already formed salt crystals.
but will tend to form many new crystals
if ions are in a supersaturated condition created by rapid water evaporation
making the energetics favorable for creating new additional crystals
rather than migrating to existing crystals.

Essentially, it takes more energy to form a sodium chloride crystal
from one sodium ion and one chloride ion
than attaching those same ions to an existing sodium ion crystal.

The effect is more pronounced in less water soluble crystals
such as calcium carbonate.

>
> Within its ability to move in the disappearing fluid, salt
> crystals are at a slightly lower energy state, than would be
> dispersed NaCl molecules.
>
> David A. Smith
>


Energy Concept in terms of free energy (kilo cal/g mole)
Sodium crystal -> sodium+ ion in water & chloride- ion in water

Free energy Free energy Free energy
Sodium crystal Sodium ion in water Chloride ion in water
-91.79 > -62.59 + -31.35

-91.79 > -93.94

More negative free energy indicates
a tendency for the reaction to go in that direction.

Stumm and Morgan
Aquatic Chemistry
goes into this type of thing in detail

Richard

Richard Saam
#15
Nov27-07, 05:02 AM
P: n/a
N:dlzc D:aol T:com (dlzc) wrote:
> Dear jim:
>
>
>
> The water molecule is polar, with a slight negative charge on one
> side. The hydrogens don't bond diametrically opposite each other
> on the oxygen. So the oxygen atom is attractive to the
> positively charged sodium, and the hydrogen atoms are attractive
> to the chloride.
>
>
>>Why do salt molecules form crystals when the salt
>>water evaporates instead of just a fine powder or dust?

>

Extremely fast water evaporation will tend to form fine powder or dust.
It is a salt nucleation process from supersaturated ion solution.
Once nucleated crystals are formed, the ions from solution
will tend to go to already formed salt crystals.
but will tend to form many new crystals
if ions are in a supersaturated condition created by rapid water evaporation
making the energetics favorable for creating new additional crystals
rather than migrating to existing crystals.

Essentially, it takes more energy to form a sodium chloride crystal
from one sodium ion and one chloride ion
than attaching those same ions to an existing sodium ion crystal.

The effect is more pronounced in less water soluble crystals
such as calcium carbonate.

>
> Within its ability to move in the disappearing fluid, salt
> crystals are at a slightly lower energy state, than would be
> dispersed NaCl molecules.
>
> David A. Smith
>


Energy Concept in terms of free energy (kilo cal/g mole)
Sodium crystal -> sodium+ ion in water & chloride- ion in water

Free energy Free energy Free energy
Sodium crystal Sodium ion in water Chloride ion in water
-91.79 > -62.59 + -31.35

-91.79 > -93.94

More negative free energy indicates
a tendency for the reaction to go in that direction.

Stumm and Morgan
Aquatic Chemistry
goes into this type of thing in detail

Richard

jim
#16
Nov29-07, 05:00 AM
P: n/a

"Tom Knight" <tk@mit.edu> wrote in message
news:vuyzlx2clvh.fsf@shaggy.csail.mit.edu...
> "Timo A. Nieminen" <timo@physics.uq.edu.au> writes:
>> Just what happens to salt in salt water?
>> Do the molecules of water and salt combine or is the salt simply
>> suspended in the water? If it is just suspended, what makes it stay
>> suspended? Why doesn't it settle to the bottom of the container?

>
> If you centrifuge salt solutions at high speed, a concentration
> gradient indeed appears. Biologists use this with cesium chloride (a
> particularly heavy ion) to set up a density gradient for separation of
> biomolecules by density.


Then why not use a device similar to a Dyson vacuum (which spins the dirt
out of air) to seperate the salt and water?


N:dlzc D:aol T:com (dlzc)
#17
Nov29-07, 05:00 AM
P: n/a
Dear Richard Saam:

"Richard Saam" <rdsaam@att.net> wrote in message
news:bJH2j.156733$kj1.98434@bgtnsc04-news.ops.worldnet.att.net...
> N:dlzc D:aol T:com (dlzc) wrote:

...
>> Within its ability to move in the disappearing
>> fluid, salt crystals are at a slightly lower energy
>> state, than would be dispersed NaCl molecules.

>
> Energy Concept in terms of free energy (kilo
> cal/g mole) Sodium crystal -> sodium+ ion in
> water & chloride- ion in water


He was asking why, when the water evaporates, fewer single
crystals are formed, rather than "salt dust". Your supplied
information does not answer that question.

> Free energy Free energy Free energy
> Sodium crystal Sodium ion in water Chloride ion in water
> -91.79 > -62.59 + -31.35
>
> -91.79 > -93.94
>
> More negative free energy indicates
> a tendency for the reaction to go in that direction.
>
> Stumm and Morgan
> Aquatic Chemistry
> goes into this type of thing in detail


David A. Smith

Gerry Quinn
#18
Nov29-07, 05:00 AM
P: n/a
In article <Orn2j.2754$k27.68@bignews2.bellsouth.net>, jim@home.net
says...

> For instance, I saw a re-run of a show last night on cable (Deep Planet)
> that showed something that may play into my questions. The scientists were
> in a specially built submersible taking pictures and film for this speacial
> of the ocean floor at great depths (10,000 feet or so). At one point, they
> came across a "pond" in the ocean. It was an actual "pond" with a shore and
> water within it that was of a much greater density than the water that they
> were already in. The film maker said that when they tried to enter the
> "pond", the submersible simply "bounced off" of it. The wanter in the
> undersea "pond" was too dense to be penetrated by the submersible.


Probably because their submersible was designed to be very close to the
density of the overlying seawater.

> In fact,
> he said that thier attempt to enter the sea-pond created "waves" across its
> surface that rippled out to it shores.
>
> He also refered to this sub-sea pond's water as "brine". Seeing as how they
> are already in the sea (a brine solution) how would this "pond" be filled
> with more dense salt water than the water that it itself was in? Shouldn't
> it reach equilibrium with the surrounding sea water through natural means?


Yes, if it is left long enough and the processes (whatever they are)
creating the dense 'pond' have stopped.

Since it clearly existed, one or both of these must not have been the
case.

Remember that the time to reach equilibrium will depend on the size of
the entities in question; what might take an hour in a coffee cup might
take months in the ocean.

- Gerry Quinn





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