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Q & A: Evaporation of Salt Water

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Most recent answer: 07/31/2008
Q:
how long does it take 1 1/2 cups of salt water to evaporate?
- evelyn (age 7)
weslaco texas hidalgo
A:
Evelyn:

The problem is that the parameters of your experiment are not very adequately defined.

When you say 1 1/2 cups of salt water, how much salt is dissolved in that water? The amount of salt in there will have a direct bearing on the boiling point of the water (as any good cook will you tell you), so that will make a big difference if you intend to boil the water away.

That brings up other ways that the description needs to be more specific before the question could have a definite answer . How do you intend to evaporate it? (On the stove, by leaving it out on a warm day, etc) What temperature will the evaporation occur at? What is the atmospheric pressure on that particular day?

(Another key parameter is how spread out the liquid will be, e.g. on a cookie sheet or in a glass. The atmospheric humidity and especiall the windiness matter as well./ mbw)

I think, to find the result, you need to actually perform the experiment. You should take the mass of a sample of reasonably pure salt (depending on what you have available. Many consumable salts have Potassium Iodide in them, for your diet ... reagent grade sodium chloride would not) and through a method you decide, evaporate it and then you'll know. You might compare different salt concentrations or evaporating it without salt in order to see general trends.

Jason

(published on 10/22/2007)

Follow-Up #1: Master equation for evaporation rate

Q:
is there any equestion that gather all these parameter to know the time of this operation , kindly provide them to me
- nizar
dubai
A:
 If such an equation were constructed, it would contain so many variables  that you probably couldn't evaluate it properly.   The temperature of the water, the rate of air flow over it, the rate of stirring of the water, the humidity of the air, and maybe some other variables all matter. If you know more or less the conditions you're interested in, you might keep all the variables constant except one, perhaps two,  and find the resulting dependencies.

LeeH and Mike W

(published on 07/31/2008)

Follow-up on this answer.