Which will evaporate first: a bowl of water that is heavily salted, or a bowl that isn't?

[metacogitans]

By 'heavily salted' I mean with table salt, NaCl, and nothing else. Both bowls sitting in the sun; assume they are both under the same conditions; both receive the same amount of sun light, one isn't sitting somewhere that's windier or anything.

And if there would be a difference, how would sea salt hold up versus table salt?

 

And bringing up wind just made me think of a bonus question: would water evaporate quicker in a location that is windy or slightly breezy? Yes, it is a question of air water-vapor saturation versus keeping heat from sunlight hitting the water close to the water as long as possible to aid in evaporation. My guess is that a slight breeze across the top of the surface of the water (but not disturbing it) would help only if the water was already very warm, on a day that is very humid.

 

If I were stuck back in ancient times, lacking a chemistry book, periodic table, and the internet of course, and had only my very limited knowledge of chemicals and materials in nature -- if I for some reason felt myself to become the Renaissance man of the age and try to develop the science of chemistry and advance it out alchemy, I personally would view the safest place to start when handling an unknown type of chemical found in, say, a new type of rock the villagers dug up or something, would be placing it in water and letting the water to evaporate, and see how it compared to sea salt - and then start trying to piece together deductions of how similar it is to sea salt. I suppose someone more knowledgable in chemistry than me would already know ways to determine what most everything if not everything is if stuck in the ancient world trying to make your own chem lab, I'm sure some know how to visually identify most substances in nature.

Perhaps if my evaporation technique proved too slow or as not giving enough useful information, I could just start researching substances by taking a flame to it; or if I got my hands on conductive wire, running electricity through things. Those are probably great ways to expose yourself to a ton of toxins and contaminate your work environment though

Edited July 30, 2015 by metacogitans

[swansont]

Given that boiling points increase when you add a solute, I would guess that the fresh water would evaporate first. Since that's a colligative property, i.e. it doesn't depend on the details of the solute, I would guess that the type of salt wouldn't matter, just the concentration of the solute.

 

edit: put another way, adding a solute lowers the vapor pressure of the solution, so it should slow the evaporation

[Sensei]

Why don't you make experiment?
Fill water two equal volume cups (or beakers if you have equipment),
add some salt to one of them,
remember which one,
and see result after day or so.
Or even record it with timelapse rendering camera in front of it.
One frame per minute f.e.

Other, faster than Sun, experiment:
- place beaker with water (+ eventually some substance) on hot plate, connected to wattmeter.
I recommend this one

It has switch to change mode, watts/voltage/amerage/energy, shows time.

 

From wattmeter you know what amount of energy you added to beaker (E=U*I*t),

use thermometer to learn what is temperature f(time),

for various solutions.

 

Remember that there will be losts from idealized closed system (beaker and water will be releasing energy to environment while you are still heating it).

 

Compare different salts results.

Compare with distilled water result.

Edited July 30, 2015 by Sensei

[Acme]

...

And bringing up wind just made me think of a bonus question: would water evaporate quicker in a location that is windy or slightly breezy? ...

Yes; wind causes an increase in evaporation.

 

Here's how professionals measure evaporation rates: Evaporation Pan

...The amount of evaporation is a function of temperature, humidity, wind and other

ambient conditions. In order to relate the evaporation to wind current or expected

conditions, the maximum and minimum temperature as well as the amount of air

passed are recorded with the evaporation. For a more exact use of the evaporation

pan it is recommended to use an additional wind path meter. ...

Pan Evaporation @ Wiki

Class A evaporation pan

[John Cuthber]

If the relative humidity is higher than about 75% the one with salt water won't evaporate at all- it will pick up water from the air.

[Elite Engineer]

bowl without salt will evaporate first. No reason to go into complex diagrams or explanations here

[Acme]

I put two small bowls filled to the brim with water out 5 hours ago, one with 4 teaspoons of salt. Currently 98ºF & 37% humidity. Evaporation from both bowls appears equal with both down ~3/32".

[Acme]

So 24 hours and the levels are virtually identical; both down 1cm. For reference I think these are 8 oz jars and I used distilled water. Here's a pic at start:

A few of additional notes:

 

I used 'sea salt' as that was what I found in the cabinet. I point out however that all salt is ultimately sea salt and even among the marketed 'sea salts' there is no consistency. See sea salt @ wiki. I rather expect there would be little difference in the experiments due to the salt 'type'.

 

As to 'heavily salted', the concentration will get higher as the water evaporates and so making the distinction even more ambiguous.

 

We hit 100ºF yesterday on my thermometer and expect the same for today.

[metacogitans]

Why don't you make experiment?

I thought of doing this, but in order to be scientific I would have to control all the variables of the experiment, which would require making sure they get the same amount of sunlight at the same angle and I'd have to calculate all that, and also set up duplicates of the same experiment to make sure there aren't inconsistencies in the results, and after all that, a decent amount of water would take days to evaporate - animals might come drink the water at night (or during the day for that matter). And I'd have to keep checking on them during the experiment, and to be honest I'm just too lazy to do all that.

So 24 hours and the levels are virtually identical; both down 1cm. For reference I think these are 8 oz jars and I used distilled water. Here's a pic at start:

A few of additional notes:

 

I used 'sea salt' as that was what I found in the cabinet. I point out however that all salt is ultimately sea salt and even among the marketed 'sea salts' there is no consistency. See sea salt @ wiki. I rather expect there would be little difference in the experiments due to the salt 'type'.

 

As to 'heavily salted', the concentration will get higher as the water evaporates and so making the distinction even more ambiguous.

 

We hit 100ºF yesterday on my thermometer and expect the same for today.

Thanks for setting up the experiment! And sounds like it's the right weather for it too.

[Acme]

I thought of doing this, but in order to be scientific I would have to control all the variables of the experiment, which would require making sure they get the same amount of sunlight at the same angle and I'd have to calculate all that, and also set up duplicates of the same experiment to make sure there aren't inconsistencies in the results, and after all that, a decent amount of water would take days to evaporate - animals might come drink the water at night (or during the day for that matter). And I'd have to keep checking on them during the experiment, and to be honest I'm just too lazy to do all that.

Good grief! Fortunately it's not as complicated as you make it out and I'm not too lazy.

Cross posted. You're welcome. Got the grandkids interested too.

Not our typical weather here in the Pacific Northwest fo sizzle. Records falling left and right.

 

One other note on the experiment, the jar with the salted water has little bubbles all around on the glass. I thumped it a few times but they won't dislodge. While minute, they surely make the level a bit higher.

[metacogitans]

I think there might be two opposing forces causing them to evaporate at the same rate: while salted water may evaporate slower, the overall percentage of mass that is H2O is less, so there is less water that has to evaporate overall.

[swansont]

I think there might be two opposing forces causing them to evaporate at the same rate: while salted water may evaporate slower, the overall percentage of mass that is H2O is less, so there is less water that has to evaporate overall.

Not if you start with the same mass of water

[Acme]

I think there might be two opposing forces causing them to evaporate at the same rate: while salted water may evaporate slower, the overall percentage of mass that is H2O is less, so there is less water that has to evaporate overall.

I'm no chemist so I can't say, but my results are contrary to everyone's claims so far. Damanble experimenters!!

 

There are some salt crystals being deposited on the jar now as the level drops. What with the clear glass and bright light I can't get a decent photo right now so will get one tonight. I thought about putting a drop of food color in each for some contrast but decided that would not be kosher midway.

Not if you start with the same mass of water

To clarify, I didn't weigh anything, rather measured by volume.

[John Cuthber]

I'm no chemist so I can't say, but my results are contrary to everyone's claims so far. Damanble experimenters!!

 

 

Can you clarify your definition of "everyone".

[Acme]

 

I'm no chemist so I can't say, but my results are contrary to everyone's claims so far. Damanble experimenters!!

Can you clarify your definition of "everyone".

 

Yes. My experiment is contrary to your post because my relative humidity was 37% and not 75%. Swans seemed to say the saltwater would evaporate slower, all else being equal, so my results are contrary to that. Elite Engineer made an unqualified 'bowl without salt will evaporate first' so again my results are contrary.

 

While I am in accord with Sensei's advice to do the experiment, he did not actually do it and made the setup rather more complicated than it need be. Half credit to you Sensei.

 

So, everyone qualified.

 

Will get a photo later tonight as promised. I went back and measured the height of the jars @ 6.5cm, so after a day ~15% of the water had evaporated from both jars. Temp was 98ºF and relative humidity 38% when I checked an hour or so ago and we've had a light breeze.

Time elapsed, 33 hours. Both levels down ~2.1cm.

 

[John Cuthber]

Lets be clear about this. I only said what would happen if the humidity was 75% or above.

You have done no experiment at 75% or above.

Your observations have nothing to do with my assertion.

They can't confirm or refute it.

(I should have pointed out that the 75% figure is for a saturated solution; for dilute solutions you need an even higher humidity for condensation to take place)

[Sensei]

Acme, get 2 graduated cylinders

http://www.ebay.com/itm/5x-Professional-Graduated-Glass-Measuring-Cylinder-Chemistry-Lab-Spout-Measure-/311307912431

You will need them in other experiments in future..

15 usd for 2 setups, 8 graduated cylinders.

 

Or pick one of these

http://www.ebay.com/bhp/graduated-cylinder

(if you want to measure volume of gases during electrolysis or other experiment producing gas, get cylinder with dismountable plastic bottom, you will place it up-side-down during experiment)

 

You will be able to tell exactly volume of liquid in each of them.

 

I would place it in front of camera and record photo per minute or hour.

Then after week watch how water is evaporating, day by day,

being able to tell volume/day or volume/hour evaporation. Enter data to OpenOffice. And compare days, compare hours.

One could use also thermometer and barometer and use them in analyze of data.

While I am in accord with Sensei's advice to do the experiment, he did not actually do it and made the setup rather more complicated than it need be. Half credit to you Sensei.

 

I wanted to accelerate experiment with electricity (hot plate), and being able to calculate energy input to beakers, to not have to wait days for some results..

 

I was doing such experiments, but with different purpose.

 

I think there might be two opposing forces causing them to evaporate at the same rate: while salted water may evaporate slower, the overall percentage of mass that is H2O is less, so there is less water that has to evaporate overall.

Not if you start with the same mass of water

 

metacogitans was referring to already on going Acme experiment. He didn't pay enough attention at setting up. I doubt he used graduated cyliders to measure initial volume of water for instance. Also didn't measure mass of salt precisely.

I put two small bowls filled to the brim with water out 5 hours ago, one with 4 teaspoons of salt.

 

I measured my teaspoon, full of NaCl salt,

on jeweler's weight that has +-0.01 grams precision,

and 1 my teaspoon has 2.54 grams.

So your 4 was approximately 10 grams (if we have equal teaspoons), with 8 oz = 236 mL of water. Maybe 250 mL?

10 g in 250 mL ~4%, I wouldn't say it's heavily salted..

Edited August 1, 2015 by Sensei

[Acme]

Lets be clear about this. I only said what would happen if the humidity was 75% or above.

You have done no experiment at 75% or above.

Your observations have nothing to do with my assertion.

They can't confirm or refute it.

(I should have pointed out that the 75% figure is for a saturated solution; for dilute solutions you need an even higher humidity for condensation to take place)

Yes, I am clear. Your assertion has nothing to do with my experiment so your assertions are contrary to my 37% relative humidity, i.e. opposed in character. You have made no assertion about what would happen in my experiment. Perfectly clear, thank you.

Acme, get 2 graduated cylinders

http://www.ebay.com/itm/5x-Professional-Graduated-Glass-Measuring-Cylinder-Chemistry-Lab-Spout-Measure-/311307912431

You will need them in other experiments in future..

15 usd for 2 setups, 8 graduated cylinders.

Thank you Sensei. I made do with what I had on hand.

 

I would place it in front of camera and record photo per minute or hour.

Then after week watch how water is evaporating, day by day,

being able to tell volume/day or volume/hour evaporation. Enter data to OpenOffice. And compare days, compare hours.

One could use also thermometer and barometer and use them in analyze of data.

By all means carry it out and report back. As the experiment was laid out in the OP, do you have an assertion on the result?

 

I wanted to accelerate experiment with electricity (hot plate), and being able to calculate energy input to beakers, to not have to wait days for some results..

Yes I understood, but I had the time and the OP described bowls sitting out in the Sun.

 

I measured my teaspoon, full of NaCl salt,

on jeweler's weight that has +-0.01 grams precision,

and 1 my teaspoon has 2.54 grams.

So your 4 was approximately 10 grams (if we have equal teaspoons), with 8 oz = 236 mL of water. Maybe 250 mL?

10 g in 250 mL ~4%, I wouldn't say it's heavily salted..

I have no such scale. As I commented earlier, "heavily" is a somewhat ambiguous term. One could (should?) conduct a series of experiments with varying concentrations. As to my teaspoon it was a standard type used in cooking. The salt was a courser grain than the usual "table" salt so your estimate of mass may be high.

.

PS Just checked experiment and overnight the salt that had crystalized on the jar went back into solution. Temperature overnight dropped to a low of 62ºF. Temperature now 70ºF, relative humidity is 52%, and barometric pressure is 29.64 inches of mercury.

Edited August 1, 2015 by Acme

[John Cuthber]

"Yes, I am clear. Your assertion has nothing to do with my experiment so your assertions are contrary to my 37% relative humidity, i.e. opposed in character. You have made no assertion about what would happen in my experiment. Perfectly clear, thank you.

 

That observation is not contrary to what I said; it's in perfect agreement with what I said.

What I said was that If the humidity is high enough then water will condense into the solution; the pretty obvious corollary is that if the humidity is low then the water will evaporate from the salt solution.

It did.

 

You might want to try again with a saturated solution of calcium chloride and see what happens.

[Acme]

 

"Yes, I am clear. Your assertion has nothing to do with my experiment so your assertions are contrary to my 37% relative humidity, i.e. opposed in character. You have made no assertion about what would happen in my experiment. Perfectly clear, thank you.

That observation is not contrary to what I said; it's in perfect agreement with what I said.

What I said was that If the humidity is high enough then water will condense into the solution; the pretty obvious corollary is that if the humidity is low then the water will evaporate from the salt solution.

It did.

 

You might want to try again with a saturated solution of calcium chloride and see what happens.

 

Whatever you say John of course. You are free to conduct your own experiment. I have conducted my experiment as described in the OP [and title]:

 

 

[Which will evaporate first: a bowl of water that is heavily salted, or a bowl that isn't?] By 'heavily salted' I mean with table salt, NaCl, and nothing else. Both bowls sitting in the sun; assume they are both under the same conditions; both receive the same amount of sun light, one isn't sitting somewhere that's windier or anything.

 

And if there would be a difference, how would sea salt hold up versus table salt? ...

My result at this point is that there is no difference in the rate of evaporation.

[Acme]

53 hours have elapsed and both jars are down 3cm. Mid-morning the relative humidity dropped to 38% and stayed there, high temp was 96ºF and the barometric pressure has remained steady @ ~29.50 inches of mercury. A small arc of salt crystals again formed on the glass.

[Moontanman]

If this experiment is carried out to it's conclusion the salted water should start to evaporate slower as the concentration of salts build up. Your result would depend on how much salt was in the water as well, enough salt and it can actually pull water out of the air if the humidity is high enough...

[Acme]

If this experiment is carried out to it's conclusion the salted water should start to evaporate slower as the concentration of salts build up. Your result would depend on how much salt was in the water as well, enough salt and it can actually pull water out of the air if the humidity is high enough...

I will continue the experiment until the jars are dry or it rains & report the result. If the salty water jar level differs from the pure water I will report it. At today's measure and report, nearly half the water had evaporated so the salt concentration -whatever it was- has nearly doubled and yet the salty water continued to evaporate at the same rate as the pure water.

 

John has already covered the high humidity and if the humidity rises I will report it.

[Acme]

This morning at the 3 day mark -10:45 am- the salted water level was down 3.1cm and the pure water level was down 3.2cm. Some arcs of precipitated salt crystals remained on the glass and are now above the water level.

 

Last night at 8pm clouds were rolling in and the relative humidity rose to 46% and temp was 85ºF.

 

Currently 75ºF, relative humidity 48%, barometric pressure 29.6 inches of mercury, and overcast sky.

 

Addendum:

3:20 pm Pacific

Didn't plan on another update until tomorrow, but one of the boys just told me we had a trace of rain this morning before I got up. Rather than stop the experiment -and presuming any precipitation would fall more or less equally into the jars- I put a cover directly above the setup in case more rain falls. Both jars are still open to the air and all light save for directly above. At my latitude -~45ºN- the Sun is never directly overhead anyway so it should be fine. Will remove it when chance of rain has passed.

 

As it is the sky currently remains overcast, temperature is still 75ºF, relative humidity 48%, and barometric pressure 29.57 inches of mercury.

 

On a side note, I'm using an electronic weather station for my readings and all this has me wanting a more advanced model that connects to my computer and also has an anemometer and rain gauge. I do have an analog rain gauge, though nothing of what fell this morning was in it.

Edited August 2, 2015 by Acme

[StringJunky]

...

On a side note, I'm using an electronic weather station for my readings and all this has me wanting a more advanced model that connects to my computer and also has an anemometer and rain gauge. I do have an analog rain gauge, though nothing of what fell this morning was in it.

Analogue doesn't work any more; rain is digital now.